image: add image.Tiled type, the Go equivalent of Plan9's repl bit.

Make ColorImage methods' receiver type be a pointer.

R=r, rsc
CC=golang-dev
https://golang.org/cl/2345043

src/pkg/exp/draw/draw.go

@@ -65,7 +65,7 @@ func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mas
 	if dst0, ok := dst.(*image.RGBA); ok {
 		if op == Over {
 			if mask == nil {
-				if src0, ok := src.(image.ColorImage); ok {
+				if src0, ok := src.(*image.ColorImage); ok {
 					drawFillOver(dst0, r, src0)
 					return
 				}
@@ -74,14 +74,14 @@ func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mas
 					return
 				}
 			} else if mask0, ok := mask.(*image.Alpha); ok {
-				if src0, ok := src.(image.ColorImage); ok {
+				if src0, ok := src.(*image.ColorImage); ok {
 					drawGlyphOver(dst0, r, src0, mask0, mp)
 					return
 				}
 			}
 		} else {
 			if mask == nil {
-				if src0, ok := src.(image.ColorImage); ok {
+				if src0, ok := src.(*image.ColorImage); ok {
 					drawFillSrc(dst0, r, src0)
 					return
 				}
@@ -149,7 +149,7 @@ func DrawMask(dst Image, r image.Rectangle, src image.Image, sp image.Point, mas
 	}
 }
 
-func drawFillOver(dst *image.RGBA, r image.Rectangle, src image.ColorImage) {
+func drawFillOver(dst *image.RGBA, r image.Rectangle, src *image.ColorImage) {
 	cr, cg, cb, ca := src.RGBA()
 	// The 0x101 is here for the same reason as in drawRGBA.
 	a := (m - ca) * 0x101
@@ -224,7 +224,7 @@ func drawCopyOver(dst *image.RGBA, r image.Rectangle, src *image.RGBA, sp image.
 	}
 }
 
-func drawGlyphOver(dst *image.RGBA, r image.Rectangle, src image.ColorImage, mask *image.Alpha, mp image.Point) {
+func drawGlyphOver(dst *image.RGBA, r image.Rectangle, src *image.ColorImage, mask *image.Alpha, mp image.Point) {
 	x0, x1 := r.Min.X, r.Max.X
 	y0, y1 := r.Min.Y, r.Max.Y
 	cr, cg, cb, ca := src.RGBA()
@@ -254,7 +254,7 @@ func drawGlyphOver(dst *image.RGBA, r image.Rectangle, src image.ColorImage, mas
 	}
 }
 
-func drawFillSrc(dst *image.RGBA, r image.Rectangle, src image.ColorImage) {
+func drawFillSrc(dst *image.RGBA, r image.Rectangle, src *image.ColorImage) {
 	if r.Dy() < 1 {
 		return
 	}

src/pkg/image/geom.go

@@ -38,6 +38,24 @@ func (p Point) Div(k int) Point {
 	return Point{p.X / k, p.Y / k}
 }
 
+// Mod returns the point q in r such that p.X-q.X is a multiple of r's width
+// and p.Y-q.Y is a multiple of r's height.
+func (p Point) Mod(r Rectangle) Point {
+	w, h := r.Dx(), r.Dy()
+	p = p.Sub(r.Min)
+	if p.X >= 0 {
+		p.X = p.X % w
+	} else {
+		p.X = w - 1 - (-1-p.X)%w
+	}
+	if p.Y >= 0 {
+		p.Y = p.Y % h
+	} else {
+		p.Y = h - 1 - (-1-p.Y)%h
+	}
+	return p.Add(r.Min)
+}
+
 // Eq returns whether p and q are equal.
 func (p Point) Eq(q Point) bool {
 	return p.X == q.X && p.Y == q.Y

src/pkg/image/names.go

@@ -21,20 +21,46 @@ type ColorImage struct {
 	C Color
 }
 
-func (c ColorImage) RGBA() (r, g, b, a uint32) {
+func (c *ColorImage) RGBA() (r, g, b, a uint32) {
 	return c.C.RGBA()
 }
 
-func (c ColorImage) ColorModel() ColorModel {
+func (c *ColorImage) ColorModel() ColorModel {
 	return ColorModelFunc(func(Color) Color { return c.C })
 }
 
-func (c ColorImage) Bounds() Rectangle { return Rectangle{Point{-1e9, -1e9}, Point{1e9, 1e9}} }
+func (c *ColorImage) Bounds() Rectangle { return Rectangle{Point{-1e9, -1e9}, Point{1e9, 1e9}} }
 
-func (c ColorImage) At(x, y int) Color { return c.C }
+func (c *ColorImage) At(x, y int) Color { return c.C }
 
 // Opaque scans the entire image and returns whether or not it is fully opaque.
-func (c ColorImage) Opaque() bool {
+func (c *ColorImage) Opaque() bool {
 	_, _, _, a := c.C.RGBA()
 	return a == 0xffff
 }
+
+func NewColorImage(c Color) *ColorImage {
+	return &ColorImage{c}
+}
+
+// A Tiled is a practically infinite-sized Image that repeats another Image in
+// both directions. Tiled{i}.At(x, y) will equal i.At(x, y) for all points
+// within i's Bounds.
+type Tiled struct {
+	I Image
+}
+
+func (t *Tiled) ColorModel() ColorModel {
+	return t.I.ColorModel()
+}
+
+func (t *Tiled) Bounds() Rectangle { return Rectangle{Point{-1e9, -1e9}, Point{1e9, 1e9}} }
+
+func (t *Tiled) At(x, y int) Color {
+	p := Point{x, y}.Mod(t.I.Bounds())
+	return t.I.At(p.X, p.Y)
+}
+
+func NewTiled(i Image) *Tiled {
+	return &Tiled{i}
+}