95 lines
2.5 KiB
Plaintext
95 lines
2.5 KiB
Plaintext
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'\" e
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'\"! eqn | mmdoc
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'\"macro stdmacro
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.ds Vn Version 1.2
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.ds Dt 6 March 1997
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.ds Re Release 1.2.0
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.ds Dp May 02 11:53
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.ds Dm 37 pickmatri
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.ds Xs 64359 5 pickmatrix.gl
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.TH GLUPICKMATRIX 3G
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.SH NAME
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.B "gluPickMatrix
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\- define a picking region
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.SH C SPECIFICATION
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void \f3gluPickMatrix\fP(
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GLdouble \fIx\fP,
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.nf
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.ta \w'\f3void \fPgluPickMatrix( 'u
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GLdouble \fIy\fP,
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GLdouble \fIdelX\fP,
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GLdouble \fIdelY\fP,
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GLint \fI*viewport\fP )
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.fi
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.EQ
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delim $$
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.EN
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.SH PARAMETERS
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.TP \w'\f2x\fP\ \f2y\fP\ \ 'u
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\f2x\fP, \f2y\fP
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Specify the center of a picking region in window coordinates.
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.TP
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\f2delX\fP, \f2delY\fP
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Specify the width and height, respectively, of the picking region in window
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coordinates.
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.TP
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\f2viewport\fP
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Specifies the current viewport (as from a \f3glGetIntegerv\fP call).
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.SH DESCRIPTION
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\%\f3gluPickMatrix\fP creates a projection matrix that can be used to restrict drawing
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to a small region of the viewport.
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This is typically useful to
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determine what objects are being drawn near the cursor.
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Use \%\f3gluPickMatrix\fP to
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restrict drawing to a small region around the cursor.
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Then,
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enter selection mode (with \f3glRenderMode\fP) and rerender the scene.
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All primitives that would have been drawn near
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the cursor are identified and stored in the selection buffer.
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.P
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The matrix created by \%\f3gluPickMatrix\fP is multiplied by the current matrix just
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as if \f3glMultMatrix\fP is called with the generated matrix.
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To effectively use the generated pick matrix for picking,
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first call \f3glLoadIdentity\fP to load an identity matrix onto the
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perspective matrix stack.
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Then call \%\f3gluPickMatrix\fP,
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and finally, call a command (such as \%\f3gluPerspective\fP)
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to multiply the perspective matrix by the pick matrix.
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.P
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When using \%\f3gluPickMatrix\fP to pick NURBS, be careful to turn off the NURBS
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property
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\%\f3GLU_AUTO_LOAD_MATRIX\fP. If \%\f3GLU_AUTO_LOAD_MATRIX\fP is not
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turned off, then any NURBS surface rendered is subdivided differently with
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the pick matrix than the way it was subdivided without the pick matrix.
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.bp
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.SH EXAMPLE
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When rendering a scene as follows:
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.sp
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.Ex
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glMatrixMode(GL_PROJECTION);
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glLoadIdentity();
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gluPerspective(...);
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glMatrixMode(GL_MODELVIEW);
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/* Draw the scene */
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.Ee
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.sp
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a portion of the viewport can be selected as a pick region like this:
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.sp
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.Ex
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glMatrixMode(GL_PROJECTION);
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glLoadIdentity();
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gluPickMatrix(x, y, width, height, viewport);
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gluPerspective(...);
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glMatrixMode(GL_MODELVIEW);
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/* Draw the scene */
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.Ee
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.SH SEE ALSO
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\f3glGet(3G)\fP,
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\f3glLoadIndentity(3G)\fP,
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\f3glMultMatrix(3G)\fP,
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\f3glRenderMode(3G)\fP,
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\%\f3gluPerspective(3G)\fP
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