xenocara/doc/xorg-docs/specs/X11/CH08

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.sp 1
.ce 3
\s+1\fBChapter 8\fP\s-1

\s+1\fBGraphics Functions\fP\s-1
.sp 2
.nr H1 8
.nr H2 0
.nr H3 0
.nr H4 0
.nr H5 0
.na
.LP
.XS
Chapter 8: Graphics Functions 
.XE
Once you have established a connection to a display,
you can use the Xlib graphics functions to:
.IP \(bu 5
Clear and copy areas
.IP \(bu 5
Draw points, lines, rectangles, and arcs
.IP \(bu 5
Fill areas
.IP \(bu 5
Manipulate fonts
.IP \(bu 5
Draw text
.IP \(bu 5
Transfer images between clients and the server
.LP
If the same drawable and GC is used for each call,
Xlib batches back-to-back calls to
.PN XDrawPoint ,
.PN XDrawLine ,
.PN XDrawRectangle ,
.PN XFillArc ,
and
.PN XFillRectangle .
Note that this reduces the total number of requests sent to the server.
.NH 2
Clearing Areas
.XS
\*(SN Clearing Areas 
.XE
.LP
Xlib provides functions that you can use to clear an area or the entire window.
Because pixmaps do not have defined backgrounds, 
they cannot be filled by using the functions described in this section.
Instead, to accomplish an analogous operation on a pixmap,
you should use 
.PN XFillRectangle ,
which sets the pixmap to a known value.
.LP
.sp
To clear a rectangular area of a given window, use
.PN XClearArea .
.IN "Areas" "clearing"
.IN "Clearing" "areas"
.IN "XClearArea" "" "@DEF@"
.sM
.FD 0
XClearArea\^(\^\fIdisplay\fP, \fIw\fP\^, \fIx\fP\^, \fIy\fP\^, \fIwidth\fP\^, \fIheight\fP\^, \fIexposures\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Window \fIw\fP\^;
.br
      int \fIx\fP\^, \fIy\fP\^;
.br
      unsigned int \fIwidth\fP\^, \fIheight\fP\^;
.br
      Bool \fIexposures\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIw\fP 1i
Specifies the window.
.ds Xy , which are relative to the origin of the window \
and specify the upper-left corner of the rectangle
.IP \fIx\fP 1i
.br
.ns
.IP \fIy\fP 1i
Specify the x and y coordinates\*(Xy.
.ds Wh , which are the dimensions of the rectangle
.IP \fIwidth\fP 1i
.br
.ns
.IP \fIheight\fP 1i
Specify the width and height\*(Wh.
.IP \fIexposures\fP 1i
Specifies a Boolean value that indicates if
.PN Expose
events are to be generated.
.LP
.eM
The
.PN XClearArea
function paints a rectangular area in the specified window according to the
specified dimensions with the window's background pixel or pixmap.
The subwindow-mode effectively is
.PN ClipByChildren . 
If width is zero, it
is replaced with the current width of the window minus x.
If height is
zero, it is replaced with the current height of the window minus y.
If the window has a defined background tile, 
the rectangle clipped by any children is filled with this tile.
If the window has
background 
.PN None , 
the contents of the window are not changed.  
In either
case, if exposures is 
.PN True , 
one or more 
.PN Expose 
events are generated for regions of the rectangle that are either visible or are
being retained in a backing store.
If you specify a window whose class is
.PN InputOnly ,
a
.PN BadMatch
error results.
.LP
.PN XClearArea
can generate
.PN BadMatch ,
.PN BadValue ,
and
.PN BadWindow 
errors.
.LP
.sp
To clear the entire area in a given window, use
.PN XClearWindow .
.IN "Window" "clearing"
.IN "Clearing" "windows"
.IN "XClearWindow" "" "@DEF@"
.sM
.FD 0
XClearWindow\^(\^\fIdisplay\fP, \fIw\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Window \fIw\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIw\fP 1i
Specifies the window.
.LP
.eM
The
.PN XClearWindow
function clears the entire area in the specified window and is
equivalent to
.PN XClearArea
(display, w, 0, 0, 0, 0, 
.PN False ).
If the window has a defined background tile, the rectangle is tiled with a
plane-mask of all ones and 
.PN GXcopy
function.
If the window has
background 
.PN None , 
the contents of the window are not changed.  
If you specify a window whose class is
.PN InputOnly ,
a
.PN BadMatch
error results. 
.LP
.PN XClearWindow
can generate
.PN BadMatch
and
.PN BadWindow 
errors.
.NH 2
Copying Areas
.XS
\*(SN Copying Areas 
.XE
.LP
Xlib provides functions that you can use to copy an area or a bit plane.
.LP
.sp
To copy an area between drawables of the same
root and depth, use
.PN XCopyArea .
.IN "Areas" "copying"
.IN "Copying" "areas"
.IN "XCopyArea" "" "@DEF@"
.sM
.FD 0
XCopyArea\^(\^\fIdisplay\fP, \fIsrc\fP\^, \fIdest\fP\^, \fIgc\fP\^, \fIsrc_x\fP\^, \fIsrc_y\fP\^, \fIwidth\fP\^, \fIheight\fP\^,  \fIdest_x\fP\^, \fIdest_y\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fIsrc\fP\^, \fIdest\fP\^;
.br
      GC \fIgc\fP\^;
.br
      int \fIsrc_x\fP\^, \fIsrc_y\fP\^;
.br
      unsigned int \fIwidth\fP\^, \fIheight\fP\^;
.br
      int \fIdest_x\fP\^, \fIdest_y\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIsrc\fP 1i
.br
.ns
.IP \fIdest\fP 1i
Specify the source and destination rectangles to be combined. 
.IP \fIgc\fP 1i
Specifies the GC.
.IP \fIsrc_x\fP 1i
.br
.ns
.IP \fIsrc_y\fP 1i
Specify the x and y coordinates, 
which are relative to the origin of the source rectangle
and specify its upper-left corner.
.ds Wh , which are the dimensions of both the source \
and destination rectangles
.IP \fIwidth\fP 1i
.br
.ns
.IP \fIheight\fP 1i
Specify the width and height\*(Wh.
.ds Dx , which are relative to the origin of the destination rectangle \
and specify its upper-left corner
.IP \fIdest_x\fP 1i
.br
.ns
.IP \fIdest_y\fP 1i
Specify the x and y coordinates\*(Dx. 
.LP
.eM
The
.PN XCopyArea
function combines the specified rectangle of src with the specified rectangle 
of dest.
The drawables must have the same root and depth,
or a
.PN BadMatch
error results.
.LP
If regions of the source rectangle are obscured and have not been
retained in backing store 
or if regions outside the boundaries of the source drawable are specified, 
those regions are not copied. 
Instead, the 
following occurs on all corresponding destination regions that are either
visible or are retained in backing store.  
If the destination is a window with a background other than 
.PN None , 
corresponding regions
of the destination are tiled with that background
(with plane-mask of all ones and
.PN GXcopy 
function).
Regardless of tiling or whether the destination is a window or a pixmap,
if graphics-exposures is 
.PN True ,
then
.PN GraphicsExpose
events for all corresponding destination regions are generated.
If graphics-exposures is 
.PN True 
but no
.PN GraphicsExpose
events are generated, a
.PN NoExpose 
event is generated.
Note that by default graphics-exposures is
.PN True
in new GCs.
.LP
This function uses these GC components: function, plane-mask, 
subwindow-mode, graphics-exposures, clip-x-origin,
clip-y-origin, and clip-mask.
.LP
.PN XCopyArea
can generate
.PN BadDrawable ,
.PN BadGC ,
and
.PN BadMatch 
errors.
.sp
.LP
To copy a single bit plane of a given drawable, use
.PN XCopyPlane .
.IN "Plane" "copying"
.IN "Copying" "planes"
.IN "XCopyPlane" "" "@DEF@"
.sM
.FD 0
XCopyPlane\^(\^\fIdisplay\fP, \fIsrc\fP\^, \fIdest\fP\^, \fIgc\fP\^, \fIsrc_x\fP\^, \fIsrc_y\fP\^, \fIwidth\fP\^, \fIheight\fP\^, \fIdest_x\fP\^, \fIdest_y\fP\^, \fIplane\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fIsrc\fP\^, \fIdest\fP\^;
.br
      GC \fIgc\fP\^;
.br
      int \fIsrc_x\fP\^, \fIsrc_y\fP\^;
.br
      unsigned int \fIwidth\fP\^, \fIheight\fP\^;
.br
      int \fIdest_x\fP\^, \fIdest_y\fP\^;
.br
      unsigned long \fIplane\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIsrc\fP 1i
.br
.ns
.IP \fIdest\fP 1i
Specify the source and destination rectangles to be combined. 
.IP \fIgc\fP 1i
Specifies the GC.
.IP \fIsrc_x\fP 1i
.br
.ns
.IP \fIsrc_y\fP 1i
Specify the x and y coordinates, 
which are relative to the origin of the source rectangle
and specify its upper-left corner.
.ds Wh , which are the dimensions of both the source and destination rectangles
.IP \fIwidth\fP 1i
.br
.ns
.IP \fIheight\fP 1i
Specify the width and height\*(Wh.
.ds Dx , which are relative to the origin of the destination rectangle \
and specify its upper-left corner
.IP \fIdest_x\fP 1i
.br
.ns
.IP \fIdest_y\fP 1i
Specify the x and y coordinates\*(Dx. 
.IP \fIplane\fP 1i
Specifies the bit plane.
You must set exactly one bit to 1.
.LP
.eM
The
.PN XCopyPlane
function uses a single bit plane of the specified source rectangle
combined with the specified GC to modify the specified rectangle of dest.
The drawables must have the same root but need not have the same depth.
If the drawables do not have the same root, a
.PN BadMatch
error results.
If plane does not have exactly one bit set to 1 and the value of plane
is not less than %2 sup n%, where \fIn\fP is the depth of src, a
.PN BadValue
error results.
.LP
Effectively, 
.PN XCopyPlane
forms a pixmap of the same depth as the rectangle of dest and with a
size specified by the source region. 
It uses the foreground/background pixels in the GC (foreground
everywhere the bit plane in src contains a bit set to 1,
background everywhere the bit plane in src contains a bit set to 0)
and the equivalent of a 
.PN CopyArea
protocol request is performed with all the same exposure semantics.
This can also be thought of as using the specified region of the source 
bit plane as a stipple with a fill-style of
.PN FillOpaqueStippled
for filling a rectangular area of the destination.
.LP
This function uses these GC components: function, plane-mask, foreground,
background, subwindow-mode, graphics-exposures, clip-x-origin, clip-y-origin,
and clip-mask.
.LP
.PN XCopyPlane
can generate
.PN BadDrawable ,
.PN BadGC ,
.PN BadMatch ,
and 
.PN BadValue 
errors.
.NH 2
Drawing Points, Lines, Rectangles, and Arcs
.XS
\*(SN Drawing Points, Lines, Rectangles, and Arcs 
.XE
.LP
Xlib provides functions that you can use to draw:
.IP \(bu 5
A single point or multiple points
.IP \(bu 5
A single line or multiple lines
.IP \(bu 5
A single rectangle or multiple rectangles
.IP \(bu 5
A single arc or multiple arcs
.LP
Some of the functions described in the following sections
use these structures:
.LP
.IN "XSegment" "" "@DEF@"
.sM
.Ds 0
.TA .5i
.ta .5i
typedef struct {
	short x1, y1, x2, y2;
} XSegment;
.De
.LP
.eM
.IN "XPoint" "" "@DEF@"
.sM
.Ds 0
.TA .5i
.ta .5i
typedef struct {
	short x, y;
} XPoint;
.De
.LP
.eM
.IN "XRectangle" "" "@DEF@"
.sM
.Ds 0
.TA .5i
.ta .5i
typedef struct {
	short x, y;
	unsigned short width, height;
} XRectangle;
.De
.LP
.eM
.IN "XArc" "" "@DEF@"
.sM
.Ds 0
.TA .5i 3i
.ta .5i 3i
typedef struct {
	short x, y;
	unsigned short width, height;
	short angle1, angle2;             /* Degrees * 64 */
} XArc;
.De
.LP
.eM
All x and y members are signed integers.
The width and height members are 16-bit unsigned integers.
You should be careful not to generate coordinates and sizes
out of the 16-bit ranges, because the protocol only has 16-bit fields
for these values.
.NH 3
Drawing Single and Multiple Points
.XS
\*(SN Drawing Single and Multiple Points 
.XE
.LP
.IN "Points" "drawing"
.IN "Drawing" "points"
.IN "XDrawPoints"
.IN "XDrawPoint"
.LP
To draw a single point in a given drawable, use
.PN XDrawPoint .
.IN "XDrawPoint" "" "@DEF@"
.sM
.FD 0
XDrawPoint\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIx\fP\^, \fIy\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      int \fIx\fP\^, \fIy\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.IP \fIx\fP 1i
.br
.ns
.IP \fIy\fP 1i
Specify the x and y coordinates where you want the point drawn.
.LP
.eM
.sp
To draw multiple points in a given drawable, use
.PN XDrawPoints .
.IN "XDrawPoints" "" "@DEF@"
.sM
.FD 0
XDrawPoints\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIpoints\fP\^, \fInpoints\fP\^, \fImode\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      XPoint *\fIpoints\fP\^;
.br
      int \fInpoints\fP\^;
.br
      int \fImode\fP\^; 
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.IP \fIpoints\fP 1i
Specifies an array of points.
.IP \fInpoints\fP 1i
Specifies the number of points in the array.
.IP \fImode\fP 1i
Specifies the coordinate mode. 
You can pass
.PN CoordModeOrigin
or
.PN CoordModePrevious .
.LP
.eM
The
.PN XDrawPoint
function uses the foreground pixel and function components of the
GC to draw a single point into the specified drawable; 
.PN XDrawPoints
draws multiple points this way.
.PN CoordModeOrigin
treats all coordinates as relative to the origin,
and
.PN CoordModePrevious
treats all coordinates after the first as relative to the previous point.
.PN XDrawPoints
draws the points in the order listed in the array.
.LP
Both functions use these GC components: function, plane-mask,
foreground, subwindow-mode, clip-x-origin, clip-y-origin, and clip-mask.
.LP
.PN XDrawPoint
can generate
.PN BadDrawable ,
.PN BadGC ,
and 
.PN BadMatch 
errors.
.PN XDrawPoints
can generate
.PN BadDrawable ,
.PN BadGC ,
.PN BadMatch ,
and
.PN BadValue 
errors.
.NH 3
Drawing Single and Multiple Lines
.XS
\*(SN Drawing Single and Multiple Lines
.XE
.LP
.IN "Lines" "drawing"
.IN "Drawing" "lines"
.IN "XDrawLine"
.IN "XDrawLines"
.IN "Polygons" "drawing"
.IN "Drawing" "polygons"
.IN "XDrawSegments"
.LP
To draw a single line between two points in a given drawable, use
.PN XDrawLine .
.IN "XDrawLine" "" "@DEF@"
.sM
.FD 0
XDrawLine\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIx1\fP\^, \fIy1\fP\^, \fIx2\fP\^, \fIy2\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      int \fIx1\fP\^, \fIy1\fP\^, \fIx2\fP\^, \fIy2\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.IP \fIx1\fP 1i
.br
.ns
.IP \fIy1\fP 1i
.br
.ns
.IP \fIx2\fP 1i
.br
.ns
.IP \fIy2\fP 1i
Specify the points (x1, y1) and (x2, y2) to be connected.
.LP
.eM
.sp
To draw multiple lines in a given drawable, use
.PN XDrawLines .
.IN "XDrawLines" "" "@DEF@"
.sM
.FD 0
XDrawLines\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIpoints\fP\^, \fInpoints\fP\^, \fImode\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      XPoint *\fIpoints\fP\^;
.br
      int \fInpoints\fP\^;
.br
      int \fImode\fP\^; 
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.IP \fIpoints\fP 1i
Specifies an array of points.
.IP \fInpoints\fP 1i
Specifies the number of points in the array.
.IP \fImode\fP 1i
Specifies the coordinate mode. 
You can pass
.PN CoordModeOrigin
or
.PN CoordModePrevious .
.LP
.eM
.sp
To draw multiple, unconnected lines in a given drawable,
use
.PN XDrawSegments .
.IN "XDrawSegments" "" "@DEF@"
.sM
.FD 0
XDrawSegments\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIsegments\fP\^, \fInsegments\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      XSegment *\fIsegments\fP\^;
.br
      int \fInsegments\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.IP \fIsegments\fP 1i
Specifies an array of segments.
.IP \fInsegments\fP 1i
Specifies the number of segments in the array.
.LP
.eM
The
.PN XDrawLine
function uses the components of the specified GC to
draw a line between the specified set of points (x1, y1) and (x2, y2).
It does not perform joining at coincident endpoints.
For any given line, 
.PN XDrawLine 
does not draw a pixel more than once.
If lines intersect, the intersecting pixels are drawn multiple times.  
.LP
The
.PN XDrawLines
function uses the components of the specified GC to draw 
npoints\-1 lines between each pair of points (point[i], point[i+1]) 
in the array of
.PN XPoint
structures.
It draws the lines in the order listed in the array.
The lines join correctly at all intermediate points, and if the first and last
points coincide, the first and last lines also join correctly.
For any given line, 
.PN XDrawLines
does not draw a pixel more than once.
If thin (zero line-width) lines intersect, 
the intersecting pixels are drawn multiple times.
If wide lines intersect, the intersecting pixels are drawn only once, as though
the entire 
.PN PolyLine 
protocol request were a single, filled shape.
.PN CoordModeOrigin
treats all coordinates as relative to the origin,
and
.PN CoordModePrevious
treats all coordinates after the first as relative to the previous point.
.LP
The
.PN XDrawSegments 
function draws multiple, unconnected lines. 
For each segment, 
.PN XDrawSegments 
draws a
line between (x1, y1) and (x2, y2).
It draws the lines in the order listed in the array of
.PN XSegment
structures and does not perform joining at coincident endpoints.
For any given line, 
.PN XDrawSegments
does not draw a pixel more than once.  
If lines intersect, the intersecting pixels are drawn multiple times.  
.LP
All three functions use these GC components:
function, plane-mask, line-width,
line-style, cap-style, fill-style, subwindow-mode,
clip-x-origin, clip-y-origin, and clip-mask.
The
.PN XDrawLines
function also uses the join-style GC component.
All three functions also use these GC mode-dependent components:
foreground, background, tile, stipple, tile-stipple-x-origin, 
tile-stipple-y-origin, dash-offset, and dash-list.
.LP
.PN XDrawLine ,
.PN XDrawLines ,
and
.PN XDrawSegments
can generate
.PN BadDrawable ,
.PN BadGC ,
and
.PN BadMatch 
errors.
.PN XDrawLines
also can generate
.PN BadValue 
errors.
.NH 3
Drawing Single and Multiple Rectangles 
.XS
\*(SN Drawing Single and Multiple Rectangles 
.XE
.LP
.IN "Rectangles" "drawing"
.IN "Drawing" "rectangles"
.IN "XDrawRectangle"
.IN "XDrawRectangles"
.LP
To draw the outline of a single rectangle in a given drawable, use
.PN XDrawRectangle .
.IN "XDrawRectangle" "" "@DEF@"
.sM
.FD 0
XDrawRectangle\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIx\fP\^, \fIy\fP\^, \fIwidth\fP\^, \fIheight\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      int \fIx\fP\^, \fIy\fP\^;
.br
      unsigned int \fIwidth\fP\^, \fIheight\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.ds Xy , which specify the upper-left corner of the rectangle
.IP \fIx\fP 1i
.br
.ns
.IP \fIy\fP 1i
Specify the x and y coordinates\*(Xy.
.ds Wh , which specify the dimensions of the rectangle
.IP \fIwidth\fP 1i
.br
.ns
.IP \fIheight\fP 1i
Specify the width and height\*(Wh.
.LP
.eM
.sp
To draw the outline of multiple rectangles
in a given drawable, use
.PN XDrawRectangles .
.IN "XDrawRectangles" "" "@DEF@"
.sM
.FD 0
XDrawRectangles\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIrectangles\fP\^, \fInrectangles\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      XRectangle \fIrectangles\fP\^[\^]\^;
.br
      int \fInrectangles\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.IP \fIrectangles\fP 1i
Specifies an array of rectangles.
.IP \fInrectangles\fP 1i
Specifies the number of rectangles in the array.
.LP
.eM
The
.PN XDrawRectangle
and
.PN XDrawRectangles
functions draw the outlines of the specified rectangle or rectangles as
if a five-point 
.PN PolyLine 
protocol request were specified for each rectangle:
.IP
[x,y] [x+width,y] [x+width,y+height] [x,y+height] [x,y]
.LP 
For the specified rectangle or rectangles, 
these functions do not draw a pixel more than once.
.PN XDrawRectangles
draws the rectangles in the order listed in the array.
If rectangles intersect,
the intersecting pixels are drawn multiple times.
.LP
Both functions use these GC components: 
function, plane-mask, line-width,
line-style, cap-style, join-style, fill-style, 
subwindow-mode, clip-x-origin, clip-y-origin, and clip-mask.
They also use these GC mode-dependent components: 
foreground, background, tile, stipple, tile-stipple-x-origin, 
tile-stipple-y-origin, dash-offset, and dash-list.
.LP
.PN XDrawRectangle
and
.PN XDrawRectangles
can generate
.PN BadDrawable ,
.PN BadGC ,
and
.PN BadMatch 
errors.
.NH 3
Drawing Single and Multiple Arcs
.XS
\*(SN Drawing Single and Multiple Arcs 
.XE
.LP
.IN "Drawing" "arcs"
.IN "XDrawArc"
.IN "Arcs" "drawing"
.IN "XDrawArcs"
.LP
.sp
To draw a single arc in a given drawable, use
.PN XDrawArc .
.IN "XDrawArc" "" "@DEF@"
.sM
.FD 0
XDrawArc\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIx\fP\^, \fIy\fP\^, \fIwidth\fP\^, \fIheight\fP\^, \fIangle1\fP\^, \fIangle2\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      int \fIx\fP\^, \fIy\fP\^;
.br
      unsigned int \fIwidth\fP\^, \fIheight\fP\^;
.br
      int \fIangle1\fP\^, \fIangle2\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.ds Xy , which are relative to the origin of the drawable \
and specify the upper-left corner of the bounding rectangle
.IP \fIx\fP 1i
.br
.ns
.IP \fIy\fP 1i
Specify the x and y coordinates\*(Xy.
.ds Wh , which are the major and minor axes of the arc
.IP \fIwidth\fP 1i
.br
.ns
.IP \fIheight\fP 1i
Specify the width and height\*(Wh.
.IP \fIangle1\fP 1i
Specifies the start of the arc relative to the three-o'clock position
from the center, in units of degrees * 64.
.IP \fIangle2\fP 1i
Specifies the path and extent of the arc relative to the start of the
arc, in units of degrees * 64.
.LP
.eM
.sp
To draw multiple arcs in a given drawable, use
.PN XDrawArcs .
.IN "XDrawArcs" "" "@DEF@"
.sM
.FD 0
XDrawArcs\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIarcs\fP\^, \fInarcs\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      XArc *\fIarcs\fP\^;
.br
      int \fInarcs\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.IP \fIarcs\fP 1i
Specifies an array of arcs.
.IP \fInarcs\fP 1i
Specifies the number of arcs in the array.
.LP
.eM
.EQ
delim %%
.EN
.PN XDrawArc
draws a single circular or elliptical arc, and 
.PN XDrawArcs
draws multiple circular or elliptical arcs.
Each arc is specified by a rectangle and two angles.  
The center of the circle or ellipse is the center of the
rectangle, and the major and minor axes are specified by the width and height.
Positive angles indicate counterclockwise motion, 
and negative angles indicate clockwise motion.  
If the magnitude of angle2 is greater than 360 degrees, 
.PN XDrawArc
or 
.PN XDrawArcs
truncates it to 360 degrees.
.LP
For an arc specified as %[ ~x, ~y, ~width , ~height, ~angle1, ~angle2 ]%, 
the origin of the major and minor axes is at 
% [ x +^ {width over 2} , ~y +^ {height over 2}  ]%, 
and the infinitely thin path describing the entire circle or ellipse 
intersects the horizontal axis at % [ x, ~y +^ {height over 2}  ]% and 
% [ x +^ width , ~y +^ { height over 2 }] %
and intersects the vertical axis at % [ x +^ { width over 2 } , ~y ]% and 
% [ x +^ { width over 2 }, ~y +^ height ]%.
These coordinates can be fractional
and so are not truncated to discrete coordinates.
The path should be defined by the ideal mathematical path.  
For a wide line with line-width lw, 
the bounding outlines for filling are given        
by the two infinitely thin paths consisting of all points whose perpendicular
distance from the path of the circle/ellipse is equal to lw/2
(which may be a fractional value).
The cap-style and join-style are applied the same as for a line
corresponding to the tangent of the circle/ellipse at the endpoint.
.LP
For an arc specified as % [ ~x, ~y, ~width, ~height, ~angle1, ~angle2  ]%,
the angles must be specified
in the effectively skewed coordinate system of the ellipse (for a
circle, the angles and coordinate systems are identical).  The
relationship between these angles and angles expressed in the normal
coordinate system of the screen (as measured with a protractor) is as
follows:
.LP
.Ds
% roman "skewed-angle" ~ = ~ atan left ( tan ( roman "normal-angle" )
 * width over height right ) +^ adjust%
.De
.LP
The skewed-angle and normal-angle are expressed in radians (rather
than in degrees scaled by 64) in the range % [ 0 , ~2 pi  ]% and where atan
returns a value in the range % [ - pi over 2 , ~pi over 2  ] %
and adjust is:
.LP
.Ds
.TA 1i 2i
.ta 1i 2i
%0%	for normal-angle in the range % [ 0 , ~pi over 2  ]%
%pi%	for normal-angle in the range % [ pi over 2 , ~{3 pi} over 2  ]%
%2 pi%	for normal-angle in the range % [ {3 pi} over 2 , ~2 pi  ]%
.De
.LP
For any given arc, 
.PN XDrawArc
and
.PN XDrawArcs
do not draw a pixel more than once.  
If two arcs join correctly and if the line-width is greater than zero 
and the arcs intersect, 
.PN XDrawArc
and
.PN XDrawArcs
do not draw a pixel more than once.
Otherwise, 
the intersecting pixels of intersecting arcs are drawn multiple times.
Specifying an arc with one endpoint and a clockwise extent draws the same pixels
as specifying the other endpoint and an equivalent counterclockwise extent,
except as it affects joins.
.LP
If the last point in one arc coincides with the first point in the following 
arc, the two arcs will join correctly.  
If the first point in the first arc coincides with the last point in the last 
arc, the two arcs will join correctly.
By specifying one axis to be zero, a horizontal or vertical line can be
drawn.
Angles are computed based solely on the coordinate system and ignore the
aspect ratio.
.LP
Both functions use these GC components: 
function, plane-mask, line-width, line-style, cap-style, join-style, 
fill-style, subwindow-mode, clip-x-origin, clip-y-origin, and clip-mask.
They also use these GC mode-dependent components: 
foreground, background, tile, stipple, tile-stipple-x-origin, 
tile-stipple-y-origin, dash-offset, and dash-list.
.LP
.PN XDrawArc
and
.PN XDrawArcs
can generate
.PN BadDrawable ,
.PN BadGC ,
and
.PN BadMatch 
errors.
.NH 2
Filling Areas
.XS
\*(SN Filling Areas 
.XE
.LP
Xlib provides functions that you can use to fill:
.IP \(bu 5
A single rectangle or multiple rectangles
.IP \(bu 5
A single polygon
.IP \(bu 5
A single arc or multiple arcs
.NH 3
Filling Single and Multiple Rectangles
.XS
\*(SN Filling Single and Multiple Rectangles 
.XE
.LP
.IN "Filling" "rectangles"
.IN "XFillRectangle"
.IN "Rectangle" "filling"
.IN "XFillRectangles"
.LP
.sp
To fill a single rectangular area in a given drawable, use
.PN XFillRectangle .
.IN "XFillRectangle" "" "@DEF@"
.sM
.FD 0 
XFillRectangle\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIx\fP\^, \fIy\fP\^, \fIwidth\fP\^, \fIheight\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      int \fIx\fP\^, \fIy\fP\^;
.br
      unsigned int \fIwidth\fP\^, \fIheight\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.ds Xy , which are relative to the origin of the drawable \
and specify the upper-left corner of the rectangle
.IP \fIx\fP 1i
.br
.ns
.IP \fIy\fP 1i
Specify the x and y coordinates\*(Xy.
.ds Wh , which are the dimensions of the rectangle to be filled
.IP \fIwidth\fP 1i
.br
.ns
.IP \fIheight\fP 1i
Specify the width and height\*(Wh.
.LP
.eM
.sp
To fill multiple rectangular areas in a given drawable, use
.PN XFillRectangles .
.IN "XFillRectangles" "" "@DEF@"
.sM
.FD 0 
XFillRectangles\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIrectangles\fP\^, \fInrectangles\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      XRectangle *\fIrectangles\fP\^;
.br
      int \fInrectangles\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.IP \fIrectangles\fP 1i
Specifies an array of rectangles.
.IP \fInrectangles\fP 1i
Specifies the number of rectangles in the array.
.LP
.eM
The
.PN XFillRectangle
and
.PN XFillRectangles
functions fill the specified rectangle or rectangles
as if a four-point 
.PN FillPolygon
protocol request were specified for each rectangle:
.LP
.Ds
[x,y] [x+width,y] [x+width,y+height] [x,y+height]
.De
.LP
Each function uses the x and y coordinates,
width and height dimensions, and GC you specify.
.LP
.PN XFillRectangles
fills the rectangles in the order listed in the array.  
For any given rectangle,
.PN XFillRectangle
and
.PN XFillRectangles
do not draw a pixel more than once.  
If rectangles intersect, the intersecting pixels are
drawn multiple times.
.LP
Both functions use these GC components: 
function, plane-mask, fill-style, subwindow-mode, 
clip-x-origin, clip-y-origin, and clip-mask.
They also use these GC mode-dependent components: 
foreground, background, tile, stipple, tile-stipple-x-origin, 
and tile-stipple-y-origin.
.LP
.PN XFillRectangle
and
.PN XFillRectangles
can generate
.PN BadDrawable ,
.PN BadGC ,
and
.PN BadMatch 
errors.
.NH 3
Filling a Single Polygon
.XS
\*(SN Filling a Single Polygon 
.XE
.LP
.sp
To fill a polygon area in a given drawable, use
.PN XFillPolygon .
.IN "Polygons" "filling"
.IN "Filling" "polygon"
.IN "XFillPolygon" "" "@DEF@"
.sM
.FD 0 
XFillPolygon\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIpoints\fP\^, \fInpoints\fP\^, \fIshape\fP\^, \fImode\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      XPoint *\fIpoints\fP\^;
.br
      int \fInpoints\fP\^;
.br
      int \fIshape\fP\^; 
.br
      int \fImode\fP\^; 
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.IP \fIpoints\fP 1i
Specifies an array of points.
.IP \fInpoints\fP 1i
Specifies the number of points in the array.
.IP \fIshape\fP 1i
Specifies a shape that helps the server to improve performance.
You can pass 
.PN Complex , 
.PN Convex , 
or 
.PN Nonconvex .
.IP \fImode\fP 1i
Specifies the coordinate mode. 
You can pass
.PN CoordModeOrigin
or
.PN CoordModePrevious .
.LP
.eM
.PN XFillPolygon 
fills the region closed by the specified path.
The path is closed
automatically if the last point in the list does not coincide with the
first point.
.PN XFillPolygon
does not draw a pixel of the region more than once.
.PN CoordModeOrigin
treats all coordinates as relative to the origin,
and
.PN CoordModePrevious
treats all coordinates after the first as relative to the previous point.
.LP
Depending on the specified shape, the following occurs: 
.IP \(bu 5
If shape is
.PN Complex , 
the path may self-intersect. 
Note that contiguous coincident points in the path are not treated 
as self-intersection.
.IP \(bu 5
If shape is
.PN Convex , 
for every pair of points inside the polygon,
the line segment connecting them does not intersect the path.
If known by the client,
specifying 
.PN Convex 
can improve performance.  
If you specify
.PN Convex 
for a path that is not convex, 
the graphics results are undefined.
.IP \(bu 5
If shape is
.PN Nonconvex , 
the path does not self-intersect, but the shape is not
wholly convex. 
If known by the client, 
specifying 
.PN Nonconvex 
instead of
.PN Complex 
may improve performance.  
If you specify
.PN Nonconvex 
for a self-intersecting path, the graphics results are undefined.
.LP
The fill-rule of the GC controls the filling behavior of 
self-intersecting polygons.
.LP
This function uses these GC components: 
function, plane-mask, fill-style, fill-rule, subwindow-mode, clip-x-origin, 
clip-y-origin, and clip-mask.
It also uses these GC mode-dependent components: 
foreground, background, tile, stipple, tile-stipple-x-origin, 
and tile-stipple-y-origin.
.LP
.PN XFillPolygon
can generate
.PN BadDrawable ,
.PN BadGC ,
.PN BadMatch ,
and
.PN BadValue 
errors.
.NH 3
Filling Single and Multiple Arcs
.XS
\*(SN Filling Single and Multiple Arcs 
.XE
.LP
.IN "XFillArc"
.IN "Arcs" "filling"
.IN "Filling" "arcs"
To fill a single arc in a given drawable, use
.PN XFillArc .
.IN "XFillArc" "" "@DEF@"
.sM
.FD 0
XFillArc\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^,  \fIx\fP\^, \fIy\fP\^, \fIwidth\fP\^, \fIheight\fP\^, \fIangle1\fP\^, \fIangle2\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      int \fIx\fP\^, \fIy\fP\^;
.br
      unsigned int \fIwidth\fP\^, \fIheight\fP\^;
.br
      int \fIangle1\fP\^, \fIangle2\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.ds Xy , which are relative to the origin of the drawable \
and specify the upper-left corner of the bounding rectangle
.IP \fIx\fP 1i
.br
.ns
.IP \fIy\fP 1i
Specify the x and y coordinates\*(Xy.
.ds Wh , which are the major and minor axes of the arc
.IP \fIwidth\fP 1i
.br
.ns
.IP \fIheight\fP 1i
Specify the width and height\*(Wh.
.IP \fIangle1\fP 1i
Specifies the start of the arc relative to the three-o'clock position
from the center, in units of degrees * 64.
.IP \fIangle2\fP 1i
Specifies the path and extent of the arc relative to the start of the
arc, in units of degrees * 64.
.LP
.eM
.sp
To fill multiple arcs in a given drawable, use
.PN XFillArcs .
.IN "XFillArcs" "" "@DEF@"
.sM
.FD 0
XFillArcs\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIarcs\fP\^, \fInarcs\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      XArc *\fIarcs\fP\^;
.br
      int \fInarcs\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.IP \fIarcs\fP 1i
Specifies an array of arcs.
.IP \fInarcs\fP 1i
Specifies the number of arcs in the array.
.LP
.eM
For each arc, 
.PN XFillArc
or
.PN XFillArcs
fills the region closed by the infinitely thin path
described by the specified arc and, depending on the 
arc-mode specified in the GC, one or two line segments. 
For 
.PN ArcChord , 
the single line segment joining the endpoints of the arc is used.  
For 
.PN ArcPieSlice ,
the two line segments joining the endpoints of the arc with the center
point are used.  
.PN XFillArcs
fills the arcs in the order listed in the array.  
For any given arc,  
.PN XFillArc
and
.PN XFillArcs
do not draw a pixel more than once.  
If regions intersect, 
the intersecting pixels are drawn multiple times.
.LP
Both functions use these GC components: 
function, plane-mask, fill-style, arc-mode, subwindow-mode, clip-x-origin, 
clip-y-origin, and clip-mask.
They also use these GC mode-dependent components: 
foreground, background, tile, stipple, tile-stipple-x-origin, 
and tile-stipple-y-origin.
.LP
.PN XFillArc
and
.PN XFillArcs
can generate
.PN BadDrawable ,
.PN BadGC ,
and
.PN BadMatch 
errors.
.NH 2
Font Metrics
.XS
\*(SN Font Metrics 
.XE
.LP
.IN "Font"
A font is a graphical description of a set of characters that are used to 
increase efficiency whenever a set of small, similar sized patterns are 
repeatedly used.
.LP
This section discusses how to:
.IP \(bu 5
Load and free fonts
.IP \(bu 5
Obtain and free font names
.IP \(bu 5
Compute character string sizes
.IP \(bu 5
Compute logical extents
.IP \(bu 5
Query character string sizes
.LP
The X server loads fonts whenever a program requests a new font.
The server can cache fonts for quick lookup.
Fonts are global across all screens in a server.
Several levels are possible when dealing with fonts.
Most applications simply use 
.PN XLoadQueryFont
to load a font and query the font metrics.
.LP
Characters in fonts are regarded as masks.
Except for image text requests,
the only pixels modified are those in which bits are set to 1 in the character.
This means that it makes sense to draw text using stipples or tiles
(for example, many menus gray-out unusable entries).
.LP
.sM
The
.PN XFontStruct
structure contains all of the information for the font
and consists of the font-specific information as well as
a pointer to an array of
.PN XCharStruct
structures for the
characters contained in the font.
The
.PN XFontStruct ,
.PN XFontProp ,
and
.PN XCharStruct
structures contain:
.LP
.IN "XCharStruct" "" "@DEF@"
.Ds 0
.TA .5i 3i
.ta .5i 3i
typedef struct {
	short lbearing;	/* origin to left edge of raster */
	short rbearing;	/* origin to right edge of raster */
	short width;	/* advance to next char's origin */
	short ascent;	/* baseline to top edge of raster */
	short descent;	/* baseline to bottom edge of raster */
	unsigned short attributes;	/* per char flags (not predefined) */
} XCharStruct;
.De
.LP
.IN "XFontProp" "" "@DEF@"
.Ds 0
.TA .5i 1i 3i
.ta .5i 1i 3i
typedef struct {
	Atom	name;
	unsigned long card32;
} XFontProp;
.De
.LP
.IN "XChar2b" "" "@DEF@"
.Ds 0
.TA .5i 3i
.ta .5i 3i
typedef struct {	/* normal 16 bit characters are two bytes */
    unsigned char byte1;
    unsigned char byte2;
} XChar2b;
.De
.LP
.IN "XFontStruct" "" "@DEF@"
.Ds 0
.TA .5i 3i
.ta .5i 3i
typedef struct {
	XExtData *ext_data;	/* hook for extension to hang data */
	Font fid;	/* Font id for this font */
	unsigned direction;	/* hint about the direction font is painted */
	unsigned min_char_or_byte2;	/* first character */
	unsigned max_char_or_byte2;	/* last character */
	unsigned min_byte1;	/* first row that exists */
	unsigned max_byte1;	/* last row that exists */
	Bool all_chars_exist;	/* flag if all characters have nonzero size */
	unsigned default_char;	/* char to print for undefined character */
	int n_properties;	/* how many properties there are */
	XFontProp *properties;	/* pointer to array of additional properties */
	XCharStruct min_bounds;	/* minimum bounds over all existing char */
	XCharStruct max_bounds;	/* maximum bounds over all existing char */
	XCharStruct *per_char;	/* first_char to last_char information */
	int ascent;	/* logical extent above baseline for spacing */
	int descent;	/* logical descent below baseline for spacing */
} XFontStruct;
.De
.LP
.eM
X supports single byte/character, two bytes/character matrix,
and 16-bit character text operations.
Note that any of these forms can be used with a font, but a
single byte/character text request can only specify a single byte
(that is, the first row of a 2-byte font).
You should view 2-byte fonts as a two-dimensional matrix of defined
characters: byte1 specifies the range of defined rows and
byte2 defines the range of defined columns of the font.
Single byte/character fonts have one row defined, and the byte2 range
specified in the structure defines a range of characters.
.LP
The bounding box of a character is defined by the 
.PN XCharStruct 
of that character.
When characters are absent from a font,
the default_char is used.
When fonts have all characters of the same size,
only the information in the
.PN XFontStruct
min and max bounds are used.
.LP
The members of the 
.PN XFontStruct 
have the following semantics:
.IP \(bu 5
The direction member can be either 
.PN FontLeftToRight 
or 
.PN FontRightToLeft . 
It is just a hint as to whether most 
.PN XCharStruct 
elements 
have a positive 
.Pn ( FontLeftToRight ) 
or a negative 
.Pn ( FontRightToLeft )
character width 
metric.
The core protocol defines no support for vertical text.
.IP \(bu 5
If the min_byte1 and max_byte1 members are both zero, min_char_or_byte2
specifies the linear character index corresponding to the first element
of the per_char array, and max_char_or_byte2 specifies the linear character
index of the last element.
.IP
If either min_byte1 or max_byte1 are nonzero, both
min_char_or_byte2 and max_char_or_byte2 are less than 256, 
and the 2-byte character index values corresponding to the
per_char array element N (counting from 0) are:
.IP
.nf
	byte1 = N/D + min_byte1
.br
	byte2 = N\\D + min_char_or_byte2
.IP
.fi
where:
.IP
.nf
        D = max_char_or_byte2 \- min_char_or_byte2 + 1
        / = integer division
        \\ = integer modulus
.fi
.IP \(bu 5
If the per_char pointer is NULL, 
all glyphs between the first and last character indexes
inclusive have the same information,
as given by both min_bounds and max_bounds.
.IP \(bu 5
If all_chars_exist is 
.PN True ,
all characters in the per_char array have nonzero bounding boxes.
.IP \(bu 5
The default_char member specifies the character that will be used when an
undefined or nonexistent character is printed.  
The default_char is a 16-bit character (not a 2-byte character).
For a font using 2-byte matrix format, 
the default_char has byte1 in the most-significant byte
and byte2 in the least significant byte.
If the default_char itself specifies an undefined or nonexistent character, 
no printing is performed for an undefined or nonexistent character.
.IP \(bu 5
The min_bounds and max_bounds members contain the most extreme values of
each individual 
.PN XCharStruct 
component over all elements of this array
(and ignore nonexistent characters).
The bounding box of the font (the smallest
rectangle enclosing the shape obtained by superimposing all of the
characters at the same origin [x,y]) has its upper-left coordinate at:
.Ds
	[x + min_bounds.lbearing, y \- max_bounds.ascent]
.De
.IP
Its width is:
.Ds
	max_bounds.rbearing \- min_bounds.lbearing
.De
.IP
Its height is:
.Ds
	max_bounds.ascent + max_bounds.descent
.De
.IP \(bu 5
The ascent member is the logical extent of the font above the baseline that is
used for determining line spacing.
Specific characters may extend beyond
this.
.IP \(bu 5
The descent member is the logical extent of the font at or below the
baseline that is used for determining line spacing.
Specific characters may extend beyond this.
.IP \(bu 5
If the baseline is at Y-coordinate y,
the logical extent of the font is inclusive between the Y-coordinate 
values (y \- font.ascent) and (y + font.descent \- 1).
Typically,
the minimum interline spacing between rows of text is given
by ascent + descent.
.LP
For a character origin at [x,y],
the bounding box of a character (that is, 
the smallest rectangle that encloses the character's shape)
described in terms of 
.PN XCharStruct 
components is a rectangle with its upper-left corner at:
.LP
.Ds
[x + lbearing, y \- ascent]
.De
.LP
Its width is:
.LP
.Ds
rbearing \- lbearing
.De
.LP
Its height is:
.LP
.Ds
ascent + descent
.De
.LP
The origin for the next character is defined to be:
.LP
.Ds
[x + width, y]
.De
.LP
The lbearing member defines the extent of the left edge of the character ink
from the origin.
The rbearing member defines the extent of the right edge of the character ink
from the origin.
The ascent member defines the extent of the top edge of the character ink
from the origin.
The descent member defines the extent of the bottom edge of the character ink
from the origin.
The width member defines the logical width of the character.
.LP
Note that the baseline (the y position of the character origin) 
is logically viewed as being the scanline just below nondescending characters. 
When descent is zero,
only pixels with Y-coordinates less than y are drawn,
and the origin is logically viewed as being coincident with the left edge of
a nonkerned character. 
When lbearing is zero,
no pixels with X-coordinate less than x are drawn.
Any of the
.PN XCharStruct
metric members could be negative.
If the width is negative,
the next character will be placed to the left of the current origin.
.LP
The X protocol does not define the interpretation of the attributes member 
in the
.PN XCharStruct
structure.
A nonexistent character is represented with all members of its
.PN XCharStruct
set to zero.
.LP
A font is not guaranteed to have any properties.
The interpretation of the property value (for example, long or unsigned long)
must be derived from \fIa priori\fP knowledge of the property. 
A basic set of font properties is specified in the X Consortium standard
\fIX Logical Font Description Conventions\fP.
.NH 3
Loading and Freeing Fonts
.XS
\*(SN Loading and Freeing Fonts 
.XE
.LP
Xlib provides functions that you can use to load fonts, get font information,
unload fonts, and free font information.
.IN "Fonts" "getting information"
.IN "Fonts" "unloading"
.IN "Fonts" "freeing font information"
A few font functions use a 
.PN GContext 
resource ID or a font ID interchangeably.
.LP
.sp
To load a given font, use
.PN XLoadFont .
.IN "XLoadFont" "" "@DEF@"
.sM
.FD 0
Font XLoadFont\^(\^\fIdisplay\fP, \fIname\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      char *\fIname\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIname\fP 1i
Specifies the name of the font,
which is a null-terminated string.
.LP
.eM
The
.PN XLoadFont
function loads the specified font and returns its associated font ID.
If the font name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
When the characters ``?'' and ``*'' are used in a font name, a
pattern match is performed and any matching font is used.
In the pattern, 
the ``?'' character will match any single character, 
and the ``*'' character will match any number of characters.
A structured format for font names is specified in the X Consortium standard 
\fIX Logical Font Description Conventions\fP.
If 
.PN XLoadFont
was unsuccessful at loading the specified font, 
a 
.PN BadName 
error results.
Fonts are not associated with a particular screen 
and can be stored as a component
of any GC.
When the font is no longer needed, call 
.PN XUnloadFont .
.LP
.PN XLoadFont
can generate
.PN BadAlloc
and
.PN BadName 
errors.
.LP
.sp
To return information about an available font, use
.PN XQueryFont .
.IN "XQueryFont" "" "@DEF@"
.sM
.FD 0
XFontStruct *XQueryFont\^(\^\fIdisplay\fP, \fIfont_ID\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      XID \fIfont_ID\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIfont_ID\fP 1i
Specifies the font ID or the 
.PN GContext
ID.
.LP
.eM
The
.PN XQueryFont
function returns a pointer to the
.PN XFontStruct
structure, which contains information associated with the font.
You can query a font or the font stored in a GC.
The font ID stored in the 
.PN XFontStruct
structure will be the 
.PN GContext 
ID, and you need to be careful when using this ID in other functions
(see
.PN XGContextFromGC ).
If the font does not exist,
.PN XQueryFont
returns NULL.
To free this data, use
.PN XFreeFontInfo .
.LP
.sp
To perform a
.PN XLoadFont
and
.PN XQueryFont
in a single operation, use
.PN XLoadQueryFont .
.IN "XLoadQueryFont" "" "@DEF@"
.sM
.FD 0
XFontStruct *XLoadQueryFont\^(\^\fIdisplay\fP, \fIname\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      char *\fIname\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIname\fP 1i
Specifies the name of the font,
which is a null-terminated string.
.LP
.eM
The
.PN XLoadQueryFont
function provides the most common way for accessing a font.
.PN XLoadQueryFont
both opens (loads) the specified font and returns a pointer to the
appropriate
.PN XFontStruct
structure.
If the font name is not in the Host Portable Character Encoding,
the result is implementation-dependent.
If the font does not exist,
.PN XLoadQueryFont
returns NULL.
.LP
.PN XLoadQueryFont
can generate a
.PN BadAlloc 
error.
.LP
.sp
To unload the font and free the storage used by the font structure
that was allocated by
.PN XQueryFont
or
.PN XLoadQueryFont ,
use
.PN XFreeFont .
.IN "XFreeFont" "" "@DEF@"
.sM
.FD 0
XFreeFont\^(\^\fIdisplay\fP, \fIfont_struct\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      XFontStruct *\fIfont_struct\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIfont_struct\fP 1i
Specifies the storage associated with the font.
.LP
.eM 
The
.PN XFreeFont
function deletes the association between the font resource ID and the specified 
font and frees the
.PN XFontStruct
structure.
The font itself will be freed when no other resource references it.
The data and the font should not be referenced again.
.LP
.PN XFreeFont
can generate a
.PN BadFont 
error.
.LP
.sp
To return a given font property, use
.PN XGetFontProperty .
.IN "XGetFontProperty" "" "@DEF@"
.sM
.FD 0
Bool XGetFontProperty\^(\^\fIfont_struct\fP\^, \^\fIatom\fP\^, \^\fIvalue_return\fP\^)
.br
      XFontStruct *\fIfont_struct\fP\^;
.br
      Atom \fIatom\fP\^;
.br
      unsigned long *\fIvalue_return\fP\^;
.FN
.IP \fIfont_struct\fP 1i
Specifies the storage associated with the font.
.IP \fIatom\fP 1i
Specifies the atom for the property name you want returned.
.IP \fIvalue_return\fP 1i
Returns the value of the font property.
.LP
.eM
Given the atom for that property,
the
.PN XGetFontProperty
function returns the value of the specified font property. 
.PN XGetFontProperty
also returns 
.PN False
if the property was not defined or 
.PN True
if it was defined.
A set of predefined atoms exists for font properties,
which can be found in
.hN X11/Xatom.h .
This set contains the standard properties associated with
a font.
Although it is not guaranteed,
it is likely that the predefined font properties will be present.
.LP
.sp
To unload a font that was loaded by
.PN XLoadFont , 
use
.PN XUnloadFont .
.IN "XUnloadFont" "" "@DEF@"
.sM
.FD 0
XUnloadFont\^(\^\fIdisplay\fP, \fIfont\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Font \fIfont\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIfont\fP 1i
Specifies the font.
.LP
.eM
The
.PN XUnloadFont
function deletes the association between the font resource ID and the specified font.
The font itself will be freed when no other resource references it.
The font should not be referenced again.
.LP
.PN XUnloadFont
can generate a
.PN BadFont 
error.
.NH 3
Obtaining and Freeing Font Names and Information
.XS
\*(SN Obtaining and Freeing Font Names and Information
.XE
.LP
You obtain font names and information by matching a wildcard specification
when querying a font type for a list of available sizes and so on.
.LP
.sp
To return a list of the available font names, use
.PN XListFonts .
.IN "XListFonts" "" "@DEF@"
.sM
.FD 0
char **XListFonts\^(\^\fIdisplay\fP, \fIpattern\fP\^, \fImaxnames\fP, \fIactual_count_return\fP\^)
.br
      Display *\^\fIdisplay\fP\^;
.br
      char *\^\fIpattern\fP\^;
.br
      int \fImaxnames\fP\^;
.br
      int *\^\fIactual_count_return\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIpattern\fP 1i
Specifies the null-terminated pattern string that can contain wildcard 
characters.
.IP \fImaxnames\fP 1i
Specifies the maximum number of names to be returned.
.IP \fIactual_count_return\fP 1i
Returns the actual number of font names.
.LP
.eM
The
.PN XListFonts
function returns an array of available font names 
(as controlled by the font search path; see
.PN XSetFontPath )
that match the string you passed to the pattern argument.
The pattern string can contain any characters,
but each asterisk (*) is a wildcard for any number of characters,
and each question mark (?) is a wildcard for a single character.
If the pattern string is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
Each returned string is null-terminated.
If the data returned by the server is in the Latin Portable Character Encoding,
then the returned strings are in the Host Portable Character Encoding.
Otherwise, the result is implementation-dependent.
If there are no matching font names,
.PN XListFonts
returns NULL.
The client should call
.PN XFreeFontNames
when finished with the result to free the memory.
.LP
.sp
To free a font name array, use
.PN XFreeFontNames .
.IN "XFreeFontNames" "" "@DEF@"
.sM
.FD 0
XFreeFontNames\^(\^\fIlist\fP\^)
.br
      char *\fIlist\fP\^[\^]\^;
.FN
.IP \fIlist\fP 1i
Specifies the array of strings you want to free.
.LP
.eM
The
.PN XFreeFontNames
function frees the array and strings returned by
.PN XListFonts 
or
.PN XListFontsWithInfo .
.LP
.sp
To obtain the names and information about available fonts, use
.PN XListFontsWithInfo .
.IN "XListFontsWithInfo" "" "@DEF@"
.sM
.FD 0
char **XListFontsWithInfo\^(\^\fIdisplay\fP, \fIpattern\fP, \fImaxnames\fP, \fIcount_return\fP, \fIinfo_return\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      char *\fIpattern\fP\^;
.br
      int \fImaxnames\fP\^;
.br
      int *\fIcount_return\fP\^;
.br
      XFontStruct **\fIinfo_return\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIpattern\fP 1i
Specifies the null-terminated pattern string that can contain wildcard 
characters.
.IP \fImaxnames\fP 1i
Specifies the maximum number of names to be returned.
.IP \fIcount_return\fP 1i
Returns the actual number of matched font names.
.IP \fIinfo_return\fP 1i
Returns the font information.
.LP
.eM
The
.PN XListFontsWithInfo
function returns a list of font names that match the specified pattern and their
associated font information.
The list of names is limited to size specified by maxnames.
The information returned for each font is identical to what
.PN XLoadQueryFont
would return except that the per-character metrics are not returned.
The pattern string can contain any characters,
but each asterisk (*) is a wildcard for any number of characters,
and each question mark (?) is a wildcard for a single character.
If the pattern string is not in the Host Portable Character Encoding,
the result is implementation-dependent.
Use of uppercase or lowercase does not matter.
Each returned string is null-terminated.
If the data returned by the server is in the Latin Portable Character Encoding,
then the returned strings are in the Host Portable Character Encoding.
Otherwise, the result is implementation-dependent.
If there are no matching font names,
.PN XListFontsWithInfo
returns NULL.
.LP
To free only the allocated name array,
the client should call
.PN XFreeFontNames .
To free both the name array and the font information array
or to free just the font information array,
the client should call
.PN XFreeFontInfo .
.LP
.sp
To free font structures and font names, use
.PN XFreeFontInfo .
.IN "XFreeFontInfo" "" "@DEF@"
.sM
.FD 0
XFreeFontInfo(\^\fInames\fP, \fIfree_info\fP, \fIactual_count\fP\^)
.br
      char **\fInames\fP\^;
.br
      XFontStruct *\fIfree_info\fP;
.br
      int \fIactual_count\fP\^;
.FN
.IP \fInames\fP 1i
Specifies the list of font names.

.IP \fIfree_info\fP 1i
Specifies the font information.

.IP \fIactual_count\fP 1i
Specifies the actual number of font names.

.LP
.eM
The
.PN XFreeFontInfo
function frees a font structure or an array of font structures
and optionally an array of font names.
If NULL is passed for names, no font names are freed.
If a font structure for an open font (returned by
.PN XLoadQueryFont )
is passed, the structure is freed,
but the font is not closed; use
.PN XUnloadFont
to close the font.
.NH 3
Computing Character String Sizes
.XS
\*(SN Computing Character String Sizes 
.XE
.LP
Xlib provides functions that you can use to compute the width,
the logical extents, 
and the server information about 8-bit and 2-byte text strings.
.IN "XTextWidth"
.IN "XTextWidth16"
The width is computed by adding the character widths of all the characters.
It does not matter if the font is an 8-bit or 2-byte font.
These functions return the sum of the character metrics in pixels.
.LP
.sp
To determine the width of an 8-bit character string, use
.PN XTextWidth .
.IN "XTextWidth" "" "@DEF@"
.sM
.FD 0
int XTextWidth\^(\^\fIfont_struct\fP\^, \fIstring\fP, \fIcount\fP\^)
.br
      XFontStruct *\fIfont_struct\fP\^;
.br
      char *\fIstring\fP\^;
.br
      int \fIcount\fP\^;
.FN
.IP \fIfont_struct\fP 1i
Specifies the font used for the width computation.
.IP \fIstring\fP 1i
Specifies the character string.
.IP \fIcount\fP 1i
Specifies the character count in the specified string.
.LP
.eM
.sp
To determine the width of a 2-byte character string, use
.PN XTextWidth16 .
.IN "XTextWidth16" "" "@DEF@"
.sM
.FD 0
int XTextWidth16\^(\^\fIfont_struct\fP\^, \fIstring\fP, \fIcount\fP\^)
.br
      XFontStruct *\fIfont_struct\fP\^;
.br
      XChar2b *\fIstring\fP\^;
.br
      int \fIcount\fP\^;
.FN
.IP \fIfont_struct\fP 1i
Specifies the font used for the width computation.
.IP \fIstring\fP 1i
Specifies the character string.
.IP \fIcount\fP 1i
Specifies the character count in the specified string.
.LP
.eM
.NH 3
Computing Logical Extents
.XS
\*(SN Computing Logical Extents 
.XE
.LP
To compute the bounding box of an 8-bit character string in a given font, use
.PN XTextExtents .
.IN "XTextExtents" "" "@DEF@"
.sM
.FD 0
XTextExtents\^(\^\fIfont_struct\fP\^, \fIstring\fP\^, \fInchars\fP\^, \
\fIdirection_return\fP, \fIfont_ascent_return\fP,
.br
              \fIfont_descent_return\fP, \fIoverall_return\fP\^)
.br
      XFontStruct *\fIfont_struct\fP\^;
.br
      char *\fIstring\fP\^;
.br
      int \fInchars\fP\^;
.br
      int *\fIdirection_return\fP\^;
.br
      int *\fIfont_ascent_return\fP, *\fIfont_descent_return\fP\^;
.br
      XCharStruct *\fIoverall_return\fP\^;

.FN
.IP \fIfont_struct\fP 1i
Specifies the 
.PN XFontStruct 
structure.
.IP \fIstring\fP 1i
Specifies the character string.
.IP \fInchars\fP 1i
Specifies the number of characters in the character string.
.IP \fIdirection_return\fP 1i
Returns the value of the direction hint
.Pn ( FontLeftToRight
or
.PN FontRightToLeft ).
.IP \fIfont_ascent_return\fP 1i
Returns the font ascent.
.IP \fIfont_descent_return\fP 1i
Returns the font descent.
.IP \fIoverall_return\fP 1i
Returns the overall size in the specified
.PN XCharStruct 
structure.
.LP
.eM
.sp
To compute the bounding box of a 2-byte character string in a given font, use
.PN XTextExtents16 .
.IN "XTextExtents16" "" "@DEF@"
.sM
.FD 0
XTextExtents16\^(\^\fIfont_struct\fP\^, \fIstring\fP\^, \fInchars\fP\^, \
\fIdirection_return\fP, \fIfont_ascent_return\fP, 
.br
                \fIfont_descent_return\fP, \fIoverall_return\fP\^)
.br
      XFontStruct *\fIfont_struct\fP\^;
.br
      XChar2b *\fIstring\fP\^;
.br
      int \fInchars\fP\^;
.br
      int *\fIdirection_return\fP\^;
.br
      int *\fIfont_ascent_return\fP, *\fIfont_descent_return\fP\^;
.br
      XCharStruct *\fIoverall_return\fP\^;

.FN
.IP \fIfont_struct\fP 1i
Specifies the 
.PN XFontStruct 
structure.
.IP \fIstring\fP 1i
Specifies the character string.
.IP \fInchars\fP 1i
Specifies the number of characters in the character string.
.IP \fIdirection_return\fP 1i
Returns the value of the direction hint
.Pn ( FontLeftToRight
or
.PN FontRightToLeft ).
.IP \fIfont_ascent_return\fP 1i
Returns the font ascent.
.IP \fIfont_descent_return\fP 1i
Returns the font descent.
.IP \fIoverall_return\fP 1i
Returns the overall size in the specified
.PN XCharStruct 
structure.
.LP
.eM
The
.PN XTextExtents
and
.PN XTextExtents16
functions 
perform the size computation locally and, thereby,
avoid the round-trip overhead of
.PN XQueryTextExtents 
and
.PN XQueryTextExtents16 .
Both functions return an
.PN XCharStruct
structure, whose members are set to the values as follows.
.LP
The ascent member is set to the maximum of the ascent metrics of all
characters in the string.
The descent member is set to the maximum of the descent metrics.
The width member is set to the sum of the character-width metrics of all
characters in the string.
For each character in the string,
let W be the sum of the character-width metrics of all characters preceding 
it in the string.
Let L be the left-side-bearing metric of the character plus W.
Let R be the right-side-bearing metric of the character plus W.
The lbearing member is set to the minimum L of all characters in the string.
The rbearing member is set to the maximum R.
.LP
For fonts defined with linear indexing rather than 2-byte matrix indexing,
each 
.PN XChar2b 
structure is interpreted as a 16-bit number with byte1 as the 
most significant byte.
If the font has no defined default character,
undefined characters in the string are taken to have all zero metrics.
.NH 3
Querying Character String Sizes
.XS
\*(SN Querying Character String Sizes 
.XE
.LP
To query the server for the bounding box of an 8-bit character string in a 
given font, use 
.PN XQueryTextExtents .
.IN "XQueryTextExtents" "" "@DEF@"
.sM
.FD 0
XQueryTextExtents\^(\^\fIdisplay\fP, \fIfont_ID\fP, \fIstring\fP, \
\fInchars\fP, \fIdirection_return\fP, \fIfont_ascent_return\fP, 
.br
                    \fIfont_descent_return\fP, \fIoverall_return\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      XID \fIfont_ID\fP\^;
.br
      char *\fIstring\fP\^;
.br
      int \fInchars\fP\^;
.br
      int *\fIdirection_return\fP\^;
.br
      int *\fIfont_ascent_return\fP, *\fIfont_descent_return\fP\^;
.br
      XCharStruct *\fIoverall_return\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIfont_ID\fP 1i
Specifies either the font ID or the 
.PN GContext
ID that contains the font.
.IP \fIstring\fP 1i
Specifies the character string.
.IP \fInchars\fP 1i
Specifies the number of characters in the character string.
.IP \fIdirection_return\fP 1i
Returns the value of the direction hint
.Pn ( FontLeftToRight
or
.PN FontRightToLeft ).
.IP \fIfont_ascent_return\fP 1i
Returns the font ascent.
.IP \fIfont_descent_return\fP 1i
Returns the font descent.
.IP \fIoverall_return\fP 1i
Returns the overall size in the specified
.PN XCharStruct 
structure.
.LP
.eM
.sp
To query the server for the bounding box of a 2-byte character string
in a given font, use
.PN XQueryTextExtents16 .
.IN "XQueryTextExtents16" "" "@DEF@"
.sM
.FD 0
XQueryTextExtents16\^(\^\fIdisplay\fP, \fIfont_ID\fP, \fIstring\fP, \
\fInchars\fP, \fIdirection_return\fP, \fIfont_ascent_return\fP, 
.br
                        \fIfont_descent_return\fP, \fIoverall_return\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      XID \fIfont_ID\fP\^;
.br
      XChar2b *\fIstring\fP\^;
.br
      int \fInchars\fP\^;
.br
      int *\fIdirection_return\fP\^;
.br
      int *\fIfont_ascent_return\fP, *\fIfont_descent_return\fP\^;
.br
      XCharStruct *\fIoverall_return\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fIfont_ID\fP 1i
Specifies either the font ID or the 
.PN GContext
ID that contains the font.
.IP \fIstring\fP 1i
Specifies the character string.
.IP \fInchars\fP 1i
Specifies the number of characters in the character string.
.IP \fIdirection_return\fP 1i
Returns the value of the direction hint
.Pn ( FontLeftToRight
or
.PN FontRightToLeft ).
.IP \fIfont_ascent_return\fP 1i
Returns the font ascent.
.IP \fIfont_descent_return\fP 1i
Returns the font descent.
.IP \fIoverall_return\fP 1i
Returns the overall size in the specified
.PN XCharStruct 
structure.
.LP
.eM
The
.PN XQueryTextExtents
and
.PN XQueryTextExtents16
functions return the bounding box of the specified 8-bit and 16-bit
character string in the specified font or the font contained in the
specified GC.
These functions query the X server and, therefore, suffer the round-trip
overhead that is avoided by
.PN XTextExtents
and 
.PN XTextExtents16 .
Both functions return a
.PN XCharStruct 
structure, whose members are set to the values as follows.
.LP
The ascent member is set to the maximum of the ascent metrics 
of all characters in the string.
The descent member is set to the maximum of the descent metrics.
The width member is set to the sum of the character-width metrics 
of all characters in the string.
For each character in the string,
let W be the sum of the character-width metrics of all characters preceding
it in the string.
Let L be the left-side-bearing metric of the character plus W.
Let R be the right-side-bearing metric of the character plus W.
The lbearing member is set to the minimum L of all characters in the string.
The rbearing member is set to the maximum R.
.LP
For fonts defined with linear indexing rather than 2-byte matrix indexing,
each 
.PN XChar2b 
structure is interpreted as a 16-bit number with byte1 as the 
most significant byte.
If the font has no defined default character,
undefined characters in the string are taken to have all zero metrics.
.LP
Characters with all zero metrics are ignored.
If the font has no defined default_char,
the undefined characters in the string are also ignored.
.LP
.PN XQueryTextExtents
and
.PN XQueryTextExtents16
can generate
.PN BadFont
and
.PN BadGC 
errors.
.NH 2
Drawing Text
.XS
\*(SN Drawing Text
.XE
.LP
This section discusses how to draw:
.IP \(bu 5
Complex text 
.IP \(bu 5
Text characters
.IP \(bu 5
Image text characters
.LP
The fundamental text functions
.PN XDrawText
and
.PN XDrawText16
use the following structures:
.LP
.IN "XTextItem" "" "@DEF@"
.sM
.Ds 0
.TA .5i 3i
.ta .5i 3i
typedef struct {
	char *chars;	/* pointer to string */
	int nchars;	/* number of characters */
	int delta;	/* delta between strings */
	Font font;	/* Font to print it in, None don't change */
} XTextItem;
.De
.LP
.IN "XTextItem16" "" "@DEF@"
.Ds 0
.TA .5i 3i
.ta .5i 3i
typedef struct {
	XChar2b *chars;	/* pointer to two-byte characters */
	int nchars;	/* number of characters */
	int delta;	/* delta between strings */
	Font font;	/* font to print it in, None don't change */
} XTextItem16;
.De
.LP
.eM
If the font member is not
.PN None ,
the font is changed before printing and also is stored in the GC.
If an error was generated during text drawing,
the previous items may have been drawn.
The baseline of the characters are drawn starting at the x and y
coordinates that you pass in the text drawing functions.
.LP
For example, consider the background rectangle drawn by
.PN XDrawImageString .
If you want the upper-left corner of the background rectangle
to be at pixel coordinate (x,y), pass the (x,y + ascent)
as the baseline origin coordinates to the text functions.
The ascent is the font ascent, as given in the
.PN XFontStruct
structure.
If you want the lower-left corner of the background rectangle
to be at pixel coordinate (x,y), pass the (x,y \- descent + 1)
as the baseline origin coordinates to the text functions.
The descent is the font descent, as given in the
.PN XFontStruct
structure.
.NH 3
Drawing Complex Text
.XS
\*(SN Drawing Complex Text 
.XE
.LP
.IN "Text" "drawing"
.IN "Drawing" "text items"
.LP
To draw 8-bit characters in a given drawable, use
.PN XDrawText .
.IN "XDrawText" "" "@DEF@"
.sM
.FD 0
XDrawText\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIx\fP\^, \fIy\fP\^, \fIitems\fP\^, \fInitems\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      int \fIx\fP\^, \fIy\fP\^;
.br
      XTextItem *\fIitems\fP\^;
.br
      int \fInitems\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.ds Xy , which are relative to the origin of the specified drawable \
and define the origin of the first character
.IP \fIx\fP 1i
.br
.ns
.IP \fIy\fP 1i
Specify the x and y coordinates\*(Xy.
.IP \fIitems\fP 1i
Specifies an array of text items.
.IP \fInitems\fP 1i
Specifies the number of text items in the array.
.LP
.eM
.sp
To draw 2-byte characters in a given drawable, use
.PN XDrawText16 .
.IN "XDrawText16" "" "@DEF@"
.sM
.FD 0
XDrawText16\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIx\fP\^, \fIy\fP\^, \fIitems\fP\^, \fInitems\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      int \fIx\fP\^, \fIy\fP\^;
.br
      XTextItem16 *\fIitems\fP\^;
.br
      int \fInitems\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.ds Xy , which are relative to the origin of the specified drawable \
and define the origin of the first character
.IP \fIx\fP 1i
.br
.ns
.IP \fIy\fP 1i
Specify the x and y coordinates\*(Xy.
.IP \fIitems\fP 1i
Specifies an array of text items.
.IP \fInitems\fP 1i
Specifies the number of text items in the array.
.LP
.eM
The
.PN XDrawText16
function is similar to
.PN XDrawText 
except that it uses 2-byte or 16-bit characters.
Both functions allow complex spacing and font shifts between counted strings.
.LP
Each text item is processed in turn.
A font member other than 
.PN None
in an item causes the font to be stored in the GC
and used for subsequent text.  
A text element delta specifies an additional change
in the position along the x axis before the string is drawn. 
The delta is always added to the character origin
and is not dependent on any characteristics of the font.
Each character image, as defined by the font in the GC, is treated as an
additional mask for a fill operation on the drawable.
The drawable is modified only where the font character has a bit set to 1.
If a text item generates a
.PN BadFont
error, the previous text items may have been drawn.
.LP
For fonts defined with linear indexing rather than 2-byte matrix indexing,
each 
.PN XChar2b
structure is interpreted as a 16-bit number with byte1 as the 
most significant byte.
.LP
Both functions use these GC components:
function, plane-mask, fill-style, font, subwindow-mode, 
clip-x-origin, clip-y-origin, and clip-mask.
They also use these GC mode-dependent components: 
foreground, background, tile, stipple, tile-stipple-x-origin, 
and tile-stipple-y-origin.
.LP
.PN XDrawText
and
.PN XDrawText16
can generate
.PN BadDrawable ,
.PN BadFont ,
.PN BadGC ,
and
.PN BadMatch 
errors.
.NH 3
Drawing Text Characters
.XS
\*(SN Drawing Text Characters 
.XE
.LP
.IN "Strings" "drawing"
.IN "Drawing" "strings"
To draw 8-bit characters in a given drawable, use
.PN XDrawString .
.IN "XDrawString" "" "@DEF@"
.sM
.FD 0
XDrawString\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIx\fP\^, \fIy\fP\^, \fIstring\fP\^, \fIlength\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      int \fIx\fP\^, \fIy\fP\^;
.br
      char *\fIstring\fP\^;
.br
      int \fIlength\fP\^; 
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.ds Xy , which are relative to the origin of the specified drawable \
and define the origin of the first character
.IP \fIx\fP 1i
.br
.ns
.IP \fIy\fP 1i
Specify the x and y coordinates\*(Xy.
.IP \fIstring\fP 1i
Specifies the character string.
.IP \fIlength\fP 1i
Specifies the number of characters in the string argument.
.LP
.eM
.sp
To draw 2-byte characters in a given drawable, use
.PN XDrawString16 .
.IN "XDrawString16" "" "@DEF@"
.sM
.FD 0
XDrawString16\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIx\fP\^, \fIy\fP\^, \fIstring\fP\^, \fIlength\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      int \fIx\fP\^, \fIy\fP\^;
.br
      XChar2b *\fIstring\fP\^;
.br
      int \fIlength\fP\^; 
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.ds Xy , which are relative to the origin of the specified drawable \
and define the origin of the first character
.IP \fIx\fP 1i
.br
.ns
.IP \fIy\fP 1i
Specify the x and y coordinates\*(Xy.
.IP \fIstring\fP 1i
Specifies the character string.
.IP \fIlength\fP 1i
Specifies the number of characters in the string argument.
.LP
.eM
Each character image, as defined by the font in the GC, is treated as an
additional mask for a fill operation on the drawable.
The drawable is modified only where the font character has a bit set to 1.
For fonts defined with 2-byte matrix indexing
and used with
.PN XDrawString16 ,
each byte is used as a byte2 with a byte1 of zero.
.LP
Both functions use these GC components: 
function, plane-mask, fill-style, font, subwindow-mode, clip-x-origin, 
clip-y-origin, and clip-mask.
They also use these GC mode-dependent components: 
foreground, background, tile, stipple, tile-stipple-x-origin, 
and tile-stipple-y-origin.
.LP
.PN XDrawString
and
.PN XDrawString16
can generate
.PN BadDrawable ,
.PN BadGC ,
and
.PN BadMatch 
errors.
.NH 3
Drawing Image Text Characters
.XS
\*(SN Drawing Image Text Characters 
.XE
.LP
.IN "Image text" "drawing"
.IN "Drawing" "image text"
Some applications, in particular terminal emulators, need to
print image text in which both the foreground and background bits of
each character are painted.
This prevents annoying flicker on many displays.
.IN "XDrawImageString"
.IN "XDrawImageString16"
.LP
.sp
To draw 8-bit image text characters in a given drawable, use
.PN XDrawImageString .
.IN "XDrawImageString" "" "@DEF@"
.sM
.FD 0
XDrawImageString\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIx\fP\^, \fIy\fP\^, \fIstring\fP\^, \fIlength\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      int \fIx\fP\^, \fIy\fP\^;
.br
      char *\fIstring\fP\^;
.br
      int \fIlength\fP\^; 
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.ds Xy , which are relative to the origin of the specified drawable \
and define the origin of the first character
.IP \fIx\fP 1i
.br
.ns
.IP \fIy\fP 1i
Specify the x and y coordinates\*(Xy.
.IP \fIstring\fP 1i
Specifies the character string.
.IP \fIlength\fP 1i
Specifies the number of characters in the string argument.
.LP
.eM
.sp
To draw 2-byte image text characters in a given drawable, use
.PN XDrawImageString16 .
.IN "XDrawImageString16" "" "@DEF@"
.sM
.FD 0
XDrawImageString16\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIx\fP\^, \fIy\fP\^, \fIstring\fP\^, \fIlength\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      GC \fIgc\fP\^;
.br
      int \fIx\fP\^, \fIy\fP\^;
.br
      XChar2b *\fIstring\fP\^;
.br
      int \fIlength\fP\^; 
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.ds Xy , which are relative to the origin of the specified drawable \
and define the origin of the first character
.IP \fIx\fP 1i
.br
.ns
.IP \fIy\fP 1i
Specify the x and y coordinates\*(Xy.
.IP \fIstring\fP 1i
Specifies the character string.
.IP \fIlength\fP 1i
Specifies the number of characters in the string argument.
.LP
.eM
The
.PN XDrawImageString16
function is similar to
.PN XDrawImageString 
except that it uses 2-byte or 16-bit characters.
Both functions also use both the foreground and background pixels 
of the GC in the destination.
.LP
The effect is first to fill a
destination rectangle with the background pixel defined in the GC and then
to paint the text with the foreground pixel.
The upper-left corner of the filled rectangle is at:
.LP
.Ds
[x, y \- font-ascent]
.De
.LP
The width is:
.LP
.Ds
overall-width
.De
.LP
The height is:
.LP
.Ds
font-ascent + font-descent
.De
.LP
The overall-width, font-ascent, and font-descent
are as would be returned by 
.PN XQueryTextExtents 
using gc and string.
The function and fill-style defined in the GC are ignored for these functions. 
The effective function is 
.PN GXcopy ,
and the effective fill-style is
.PN FillSolid .
.LP
For fonts defined with 2-byte matrix indexing
and used with
.PN XDrawImageString ,
each byte is used as a byte2 with a byte1 of zero.
.LP
Both functions use these GC components: 
plane-mask, foreground, background, font, subwindow-mode, clip-x-origin, 
clip-y-origin, and clip-mask.
.LP
.PN XDrawImageString
and
.PN XDrawImageString16
can generate
.PN BadDrawable ,
.PN BadGC ,
and
.PN BadMatch 
errors.
.LP
.NH 2
Transferring Images between Client and Server
.XS
\*(SN Transferring Images between Client and Server 
.XE
.LP
Xlib provides functions that you can use to transfer images between a client 
and the server.
Because the server may require diverse data formats, 
Xlib provides an image object that fully describes the data in memory 
and that provides for basic operations on that data.  
You should reference the data 
through the image object rather than referencing the data directly.
However, some implementations of the Xlib library may efficiently deal with 
frequently used data formats by replacing
functions in the procedure vector with special case functions.
Supported operations include destroying the image, getting a pixel,
storing a pixel, extracting a subimage of an image, and adding a constant
to an image (see section 16.8).
.LP
All the image manipulation functions discussed in this section make use of 
the 
.PN XImage 
structure,
which describes an image as it exists in the client's memory.
.LP
.IN "XImage" "" "@DEF@"
.sM
.Ds 0
.TA .5i 1i 3i
.ta .5i 1i 3i
typedef struct _XImage {
	int width, height;		/* size of image */
	int xoffset;		/* number of pixels offset in X direction */
	int format;		/* XYBitmap, XYPixmap, ZPixmap */
	char *data;		/* pointer to image data */
	int byte_order;		/* data byte order, LSBFirst, MSBFirst */
	int bitmap_unit;		/* quant. of scanline 8, 16, 32 */
	int bitmap_bit_order;		/* LSBFirst, MSBFirst */
	int bitmap_pad;		/* 8, 16, 32 either XY or ZPixmap */
	int depth;		/* depth of image */
	int bytes_per_line;		/* accelerator to next scanline */
	int bits_per_pixel;		/* bits per pixel (ZPixmap) */
	unsigned long red_mask;		/* bits in z arrangement */
	unsigned long green_mask;
	unsigned long blue_mask;
	XPointer obdata;	/* hook for the object routines to hang on */
	struct funcs {		/* image manipulation routines */
		struct _XImage *(*create_image)();
		int (*destroy_image)();
		unsigned long (*get_pixel)();
		int (*put_pixel)();
		struct _XImage *(*sub_image)();
		int (*add_pixel)();
	} f;
} XImage;
.De
.LP
.eM
.sp
To initialize the image manipulation routines of an image structure, use
.PN XInitImage .
.IN "XInitImage" "" "@DEF@"
.sM
.FD 0
Status XInitImage\^(\^\fIimage\fP\^)
.br
      XImage *\fIimage\fP\^;
.FN
.IP \fIximage\fP 1i
Specifies the image.
.LP
.eM
The
.PN XInitImage
function initializes the internal image manipulation routines of an
image structure, based on the values of the various structure members.
All fields other than the manipulation routines must already be initialized.
If the bytes_per_line member is zero,
.PN XInitImage
will assume the image data is contiguous in memory and set the
bytes_per_line member to an appropriate value based on the other
members; otherwise, the value of bytes_per_line is not changed.
All of the manipulation routines are initialized to functions
that other Xlib image manipulation functions need to operate on the
type of image specified by the rest of the structure.
.LP
This function must be called for any image constructed by the client
before passing it to any other Xlib function.
Image structures created or returned by Xlib do not need to be
initialized in this fashion.
.LP
This function returns a nonzero status if initialization of the
structure is successful.  It returns zero if it detected some error
or inconsistency in the structure, in which case the image is not changed.
.LP
.sp
To combine an image with a rectangle of a drawable on the display,
use
.PN XPutImage .
.IN "XPutImage" "" "@DEF@"
.sM
.FD 0
XPutImage\^(\^\fIdisplay\fP, \fId\fP\^, \fIgc\fP\^, \fIimage\fP\^, \fIsrc_x\fP, \fIsrc_y\fP, \fIdest_x\fP\^, \fIdest_y\fP\^, \fIwidth\fP\^, \fIheight\fP\^)
.br
        Display *\fIdisplay\fP\^;
.br
        Drawable \fId\fP\^;
.br
        GC \fIgc\fP\^;
.br
        XImage *\fIimage\fP\^;
.br
        int \fIsrc_x\fP\^, \fIsrc_y\fP\^;
.br
        int \fIdest_x\fP\^, \fIdest_y\fP\^;
.br
        unsigned int \fIwidth\fP\^, \fIheight\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.IP \fIgc\fP 1i
Specifies the GC.
.IP \fIimage\fP 1i
Specifies the image you want combined with the rectangle. 
.IP \fIsrc_x\fP 1i
Specifies the offset in X from the left edge of the image defined
by the 
.PN XImage 
structure.
.IP \fIsrc_y\fP 1i
Specifies the offset in Y from the top edge of the image defined
by the 
.PN XImage 
structure.
.ds Dx , which are relative to the origin of the drawable \
and are the coordinates of the subimage
.IP \fIdest_x\fP 1i
.br
.ns
.IP \fIdest_y\fP 1i
Specify the x and y coordinates\*(Dx. 
.ds Wh \ of the subimage, which define the dimensions of the rectangle
.IP \fIwidth\fP 1i
.br
.ns
.IP \fIheight\fP 1i
Specify the width and height\*(Wh.
.LP
.eM
The
.PN XPutImage
function
combines an image with a rectangle of the specified drawable.
The section of the image defined by the src_x, src_y, width, and height 
arguments is drawn on the specified part of the drawable.
If 
.PN XYBitmap 
format is used, the depth of the image must be one,
or a
.PN BadMatch 
error results.
The foreground pixel in the GC defines the source for the one bits in the image,
and the background pixel defines the source for the zero bits.
For 
.PN XYPixmap 
and 
.PN ZPixmap , 
the depth of the image must match the depth of the drawable,
or a
.PN BadMatch
error results.
.LP
If the characteristics of the image (for example, byte_order and bitmap_unit)
differ from what the server requires,
.PN XPutImage 
automatically makes the appropriate
conversions.
.LP
This function uses these GC components: 
function, plane-mask, subwindow-mode, clip-x-origin, clip-y-origin, 
and clip-mask.
It also uses these GC mode-dependent components:
foreground and background.
.LP
.PN XPutImage
can generate
.PN BadDrawable ,
.PN BadGC ,
.PN BadMatch ,
and
.PN BadValue 
errors.
.LP
.sp
To return the contents of a rectangle in a given drawable on the display,
use
.PN XGetImage .
This function specifically supports rudimentary screen dumps.
.IN "XGetImage" "" "@DEF@"
.sM
.FD 0
XImage *XGetImage\^(\^\fIdisplay\fP, \fId\fP\^, \fIx\fP\^, \fIy\fP\^, \fIwidth\fP\^, \fIheight\fP\^, \fIplane_mask\fP, \fIformat\fP\^)
.br
        Display *\fIdisplay\fP\^;
.br
        Drawable \fId\fP\^;
.br
        int \fIx\fP\^, \fIy\fP\^;
.br
        unsigned int \fIwidth\fP\^, \fIheight\fP\^;
.br
        unsigned long \fIplane_mask\fP\^;
.br
        int \fIformat\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.ds Xy , which are relative to the origin of the drawable \
and define the upper-left corner of the rectangle
.IP \fIx\fP 1i
.br
.ns
.IP \fIy\fP 1i
Specify the x and y coordinates\*(Xy.
.ds Wh \ of the subimage, which define the dimensions of the rectangle
.IP \fIwidth\fP 1i
.br
.ns
.IP \fIheight\fP 1i
Specify the width and height\*(Wh.
.IP \fIplane_mask\fP 1i
Specifies the plane mask.
.\" *** JIM: NEED MORE INFO FOR THIS. ***
.IP \fIformat\fP 1i
Specifies the format for the image.
You can pass
.PN XYPixmap
or 
.PN ZPixmap .
.LP
.eM
The
.PN XGetImage
function returns a pointer to an
.PN XImage
structure.
This structure provides you with the contents of the specified rectangle of
the drawable in the format you specify.
If the format argument is 
.PN XYPixmap ,
the image contains only the bit planes you passed to the plane_mask argument.
If the plane_mask argument only requests a subset of the planes of the
display, the depth of the returned image will be the number of planes
requested.
If the format argument is 
.PN ZPixmap ,
.PN XGetImage
returns as zero the bits in all planes not 
specified in the plane_mask argument.
The function performs no range checking on the values in plane_mask and ignores
extraneous bits.
.LP
.PN XGetImage
returns the depth of the image to the depth member of the
.PN XImage
structure.
The depth of the image is as specified when the drawable was created,
except when getting a subset of the planes in 
.PN XYPixmap
format, when the depth is given by the number of bits set to 1 in plane_mask.
.LP
If the drawable is a pixmap, 
the given rectangle must be wholly contained within the pixmap, 
or a
.PN BadMatch
error results.
If the drawable is a window, 
the window must be viewable, 
and it must be the case that if there were no inferiors or overlapping windows,
the specified rectangle of the window would be fully visible on the screen
and wholly contained within the outside edges of the window,
or a
.PN BadMatch
error results.
Note that the borders of the window can be included and read with
this request.
If the window has backing-store, the backing-store contents are
returned for regions of the window that are obscured by noninferior
windows. 
If the window does not have backing-store,
the returned contents of such obscured regions are undefined.
The returned contents of visible regions of inferiors
of a different depth than the specified window's depth are also undefined.
The pointer cursor image is not included in the returned contents.
If a problem occurs,
.PN XGetImage
returns NULL.
.LP
.PN XGetImage
can generate
.PN BadDrawable ,
.PN BadMatch ,
and
.PN BadValue 
errors.
.sp
.LP
To copy the contents of a rectangle on the display
to a location within a preexisting image structure, use
.PN XGetSubImage .
.IN "XGetSubImage" "" "@DEF@"
.sM
.FD 0
XImage *XGetSubImage\^(\^\fIdisplay\fP, \fId\fP\^, \fIx\fP\^, \fIy\fP\^, \fIwidth\fP\^, \fIheight\fP\^, \fIplane_mask\fP, \fIformat\fP\^, \fIdest_image\fP\^, \fIdest_x\fP\^, 
.br
                     \fIdest_y\fP\^)
.br
      Display *\fIdisplay\fP\^;
.br
      Drawable \fId\fP\^;
.br
      int \fIx\fP\^, \fIy\fP\^;
.br
      unsigned int \fIwidth\fP\^, \fIheight\fP\^;
.br
      unsigned long \fIplane_mask\fP\^;
.br
      int \fIformat\fP\^;
.br
      XImage *\fIdest_image\fP\^;
.br
      int \fIdest_x\fP\^, \fIdest_y\fP\^;
.FN
.IP \fIdisplay\fP 1i
Specifies the connection to the X server.
.IP \fId\fP 1i
Specifies the drawable. 
.ds Xy , which are relative to the origin of the drawable \
and define the upper-left corner of the rectangle
.IP \fIx\fP 1i
.br
.ns
.IP \fIy\fP 1i
Specify the x and y coordinates\*(Xy.
.ds Wh \ of the subimage, which define the dimensions of the rectangle
.IP \fIwidth\fP 1i
.br
.ns
.IP \fIheight\fP 1i
Specify the width and height\*(Wh.
.IP \fIplane_mask\fP 1i
Specifies the plane mask.
.\" *** JIM: NEED MORE INFO FOR THIS. ***
.IP \fIformat\fP 1i
Specifies the format for the image.
You can pass
.PN XYPixmap
or 
.PN ZPixmap .
.IP \fIdest_image\fP 1i
Specifies the destination image.
.ds Dx , which are relative to the origin of the destination rectangle, \
specify its upper-left corner, and determine where the subimage \
is placed in the destination image
.IP \fIdest_x\fP 1i
.br
.ns
.IP \fIdest_y\fP 1i
Specify the x and y coordinates\*(Dx. 
.LP
.eM
The 
.PN XGetSubImage 
function updates dest_image with the specified subimage in the same manner as 
.PN XGetImage . 
If the format argument is 
.PN XYPixmap ,
the image contains only the bit planes you passed to the plane_mask argument.
If the format argument is 
.PN ZPixmap ,
.PN XGetSubImage
returns as zero the bits in all planes not 
specified in the plane_mask argument.
The function performs no range checking on the values in plane_mask and ignores
extraneous bits.
As a convenience,
.PN XGetSubImage
returns a pointer to the same
.PN XImage
structure specified by dest_image.
.LP
The depth of the destination
.PN XImage
structure must be the same as that of the drawable.
If the specified subimage does not fit at the specified location
on the destination image, the right and bottom edges are clipped.
If the drawable is a pixmap,
the given rectangle must be wholly contained within the pixmap,
or a
.PN BadMatch
error results.
If the drawable is a window, 
the window must be viewable, 
and it must be the case that if there were no inferiors or overlapping windows,
the specified rectangle of the window would be fully visible on the screen
and wholly contained within the outside edges of the window,
or a
.PN BadMatch
error results.
If the window has backing-store, 
then the backing-store contents are returned for regions of the window 
that are obscured by noninferior windows. 
If the window does not have backing-store, 
the returned contents of such obscured regions are undefined.
The returned contents of visible regions of inferiors
of a different depth than the specified window's depth are also undefined.
If a problem occurs,
.PN XGetSubImage
returns NULL.
.LP
.PN XGetSubImage
can generate
.PN BadDrawable ,
.PN BadGC ,
.PN BadMatch ,
and
.PN BadValue 
errors.
.bp