Introduce the image package.

R=rsc
APPROVED=r,rsc
DELTA=244  (244 added, 0 deleted, 0 changed)
OCL=33733
CL=33940

src/pkg/Make.deps

@@ -32,6 +32,7 @@ hash.install: io.install
 hash/adler32.install: hash.install os.install
 hash/crc32.install: hash.install os.install
 http.install: bufio.install bytes.install container/vector.install fmt.install io.install log.install net.install os.install path.install strconv.install strings.install utf8.install
+image.install:
 io.install: bytes.install os.install strings.install sync.install
 json.install: bytes.install container/vector.install fmt.install math.install reflect.install strconv.install strings.install utf8.install
 log.install: fmt.install io.install os.install runtime.install time.install

src/pkg/Makefile

@@ -46,6 +46,7 @@ DIRS=\
 	hash/adler32\
 	hash/crc32\
 	http\
+	image\
 	io\
 	json\
 	log\

src/pkg/image/Makefile

@@ -0,0 +1,12 @@
+# Copyright 2009 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+include $(GOROOT)/src/Make.$(GOARCH)
+
+TARG=image
+GOFILES=\
+	color.go\
+	image.go\
+
+include $(GOROOT)/src/Make.pkg

src/pkg/image/color.go

@@ -0,0 +1,90 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package image
+
+// TODO(nigeltao): Clarify semantics wrt premultiplied vs unpremultiplied colors.
+// It's probably also worth thinking about floating-point color models.
+
+// All Colors can convert themselves, with a possible loss of precision, to 128-bit RGBA.
+type Color interface {
+	RGBA() (r, g, b, a uint32);
+}
+
+// An RGBAColor represents a traditional 32-bit color, having 8 bits for each of red, green, blue and alpha.
+type RGBAColor struct {
+	R, G, B, A uint8;
+}
+
+func (c RGBAColor) RGBA() (r, g, b, a uint32) {
+	r = uint32(c.R);
+	r |= r<<8;
+	r |= r<<16;
+	g = uint32(c.G);
+	g |= g<<8;
+	g |= g<<16;
+	b = uint32(c.B);
+	b |= b<<8;
+	b |= b<<16;
+	a = uint32(c.A);
+	a |= a<<8;
+	a |= a<<16;
+	return;
+}
+
+// An RGBA64Color represents a 64-bit color, having 16 bits for each of red, green, blue and alpha.
+type RGBA64Color struct {
+	R, G, B, A uint16;
+}
+
+func (c RGBA64Color) RGBA() (r, g, b, a uint32) {
+	r = uint32(c.R);
+	r |= r<<16;
+	g = uint32(c.G);
+	g |= g<<16;
+	b = uint32(c.B);
+	b |= b<<16;
+	a = uint32(c.A);
+	a |= a<<16;
+	return;
+}
+
+// A ColorModel can convert foreign Colors, with a possible loss of precision, to a Color
+// from its own color model.
+type ColorModel interface {
+	Convert(c Color) Color;
+}
+
+// The ColorModelFunc type is an adapter to allow the use of an ordinary
+// color conversion function as a ColorModel.  If f is such a function,
+// ColorModelFunc(f) is a ColorModel object that invokes f to implement
+// the conversion.
+type ColorModelFunc func(Color) Color
+
+func (f ColorModelFunc) Convert(c Color) Color {
+	return f(c);
+}
+
+func toRGBAColor(c Color) Color {
+	if _, ok := c.(RGBAColor); ok {	// no-op conversion
+		return c;
+	}
+	r, g, b, a := c.RGBA();
+	return RGBAColor{ uint8(r>>24), uint8(g>>24), uint8(b>>24), uint8(a>>24) };
+}
+
+func toRGBA64Color(c Color) Color {
+	if _, ok := c.(RGBA64Color); ok {	// no-op conversion
+		return c;
+	}
+	r, g, b, a := c.RGBA();
+	return RGBA64Color{ uint16(r>>16), uint16(g>>16), uint16(b>>16), uint16(a>>16) };
+}
+
+// The ColorModel associated with RGBAColor.
+var RGBAColorModel ColorModel = ColorModelFunc(toRGBAColor);
+
+// The ColorModel associated with RGBA64Color.
+var RGBA64ColorModel ColorModel = ColorModelFunc(toRGBA64Color);
+

src/pkg/image/image.go

@@ -0,0 +1,140 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// The image package implements a basic 2-D image library.
+package image
+
+// An Image is a rectangular grid of Colors drawn from a ColorModel.
+type Image interface {
+	ColorModel() ColorModel;
+	Width() int;
+	Height() int;
+	// At(0, 0) returns the upper-left pixel of the grid.
+	// At(Width()-1, Height()-1) returns the lower-right pixel.
+	At(x, y int) Color;
+}
+
+// An RGBA is an in-memory image backed by a 2-D slice of RGBAColor values.
+type RGBA struct {
+	// The Pixel field's indices are y first, then x, so that At(x, y) == Pixel[y][x].
+	Pixel [][]RGBAColor;
+}
+
+func (p *RGBA) ColorModel() ColorModel {
+	return RGBAColorModel;
+}
+
+func (p *RGBA) Width() int {
+	if len(p.Pixel) == 0 {
+		return 0;
+	}
+	return len(p.Pixel[0]);
+}
+
+func (p *RGBA) Height() int {
+	return len(p.Pixel);
+}
+
+func (p *RGBA) At(x, y int) Color {
+	return p.Pixel[y][x];
+}
+
+func (p *RGBA) Set(x, y int, c Color) {
+	p.Pixel[y][x] = toRGBAColor(c).(RGBAColor);
+}
+
+// An RGBA64 is an in-memory image backed by a 2-D slice of RGBA64Color values.
+type RGBA64 struct {
+	// The Pixel field's indices are y first, then x, so that At(x, y) == Pixel[y][x].
+	Pixel [][]RGBA64Color;
+}
+
+func (p *RGBA64) ColorModel() ColorModel {
+	return RGBA64ColorModel;
+}
+
+func (p *RGBA64) Width() int {
+	if len(p.Pixel) == 0 {
+		return 0;
+	}
+	return len(p.Pixel[0]);
+}
+
+func (p *RGBA64) Height() int {
+	return len(p.Pixel);
+}
+
+func (p *RGBA64) At(x, y int) Color {
+	return p.Pixel[y][x];
+}
+
+func (p *RGBA64) Set(x, y int, c Color) {
+	p.Pixel[y][x] = toRGBA64Color(c).(RGBA64Color);
+}
+
+// A PalettedColorModel represents a fixed palette of colors.
+type PalettedColorModel []Color;
+
+func diff(a, b uint32) uint32 {
+	if a > b {
+		return a - b;
+	}
+	return b - a;
+}
+
+// Convert returns the palette color closest to c in Euclidean R,G,B space.
+func (p PalettedColorModel) Convert(c Color) Color {
+	if len(p) == 0 {
+		return nil;
+	}
+	// TODO(nigeltao): Revisit the "pick the palette color which minimizes sum-squared-difference"
+	// algorithm when the premultiplied vs unpremultiplied issue is resolved.
+	// Currently, we only compare the R, G and B values, and ignore A.
+	cr, cg, cb, ca := c.RGBA();
+	// Shift by 17 bits to avoid potential uint32 overflow in sum-squared-difference.
+	cr >>= 17;
+	cg >>= 17;
+	cb >>= 17;
+	result := Color(nil);
+	bestSSD := uint32(1<<32 - 1);
+	for _, v := range p {
+		vr, vg, vb, va := v.RGBA();
+		vr >>= 17;
+		vg >>= 17;
+		vb >>= 17;
+		dr, dg, db := diff(cr, vr), diff(cg, vg), diff(cb, vb);
+		ssd := (dr * dr) + (dg * dg) + (db * db);
+		if ssd < bestSSD {
+			bestSSD = ssd;
+			result = v;
+		}
+	}
+	return result;
+}
+
+// A Paletted is an in-memory image backed by a 2-D slice of byte values and a PalettedColorModel.
+type Paletted struct {
+	// The Pixel field's indices are y first, then x, so that At(x, y) == Palette[Pixel[y][x]].
+	Pixel [][]byte;
+	Palette PalettedColorModel;
+}
+
+func (p *Paletted) ColorModel() ColorModel {
+	return p.Palette;
+}
+
+func (p *Paletted) Width() int {
+	if len(p.Pixel) == 0 {
+		return 0;
+	}
+	return len(p.Pixel[0]);
+}
+
+func (p *Paletted) Height() int {
+	return len(p.Pixel);
+}
+
+func (p *Paletted) At(x, y int) Color {
+	return p.Palette[p.Pixel[y][x]];
+}