internal/graphics: add built-in Kage functions

This change adds these Kage functions:

* imageDstOrigin
* imageDstSrc
* imageSrcNOrigin
* imageSrcNSrc

and deprecates these functions:

* imageDstRegionOnTexture
* imageSrcRegionOnTexture

Closes #1870

examples/flappy/crt.go

@@ -33,8 +33,9 @@ func Warp(pos vec2) vec2 {
 
 func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 	// Adjust the texture position to [0, 1].
+	origin := imageSrc0Origin()
+	size := imageSrc0Size()
 	pos := texCoord
-	origin, size := imageSrcRegionOnTexture()
 	pos -= origin
 	pos /= size
 

examples/shader/chromaticaberration.go

@@ -22,8 +22,7 @@ var Time float
 var Cursor vec2
 
 func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
-	_, dstSize := imageDstRegionOnTexture()
+	center := imageDstSize() / 2
-	center := dstSize / 2
 	amount := (center - Cursor) / 10
 	var clr vec3
 	clr.r = imageSrc2At(texCoord + amount).r

examples/shader/default.go

@@ -22,9 +22,8 @@ var Time float
 var Cursor vec2
 
 func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
-	dstOrigin, dstSize := imageDstRegionOnTexture()
+	pos := (position.xy - imageDstOrigin()) / imageDstSize()
-	pos := (position.xy - dstOrigin) / dstSize
+	pos += Cursor / imageDstSize() / 4
-	pos += Cursor / dstSize / 4
 	clr := 0.0
 	clr += sin(pos.x*cos(Time/15)*80) + cos(pos.y*cos(Time/15)*10)
 	clr += sin(pos.y*sin(Time/10)*40) + cos(pos.x*sin(Time/25)*40)

examples/shader/lighting.go

@@ -22,8 +22,7 @@ var Time float
 var Cursor vec2
 
 func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
-	dstOrigin, _ := imageDstRegionOnTexture()
+	pos := position.xy - imageDstOrigin()
-	pos := position.xy - dstOrigin
 
 	lightpos := vec3(Cursor, 50)
 	lightdir := normalize(lightpos - vec3(pos, 0))

examples/shader/radialblur.go

@@ -22,8 +22,7 @@ var Time float
 var Cursor vec2
 
 func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
-	dstOrigin, _ := imageDstRegionOnTexture()
+	pos := position.xy - imageDstOrigin()
-	pos := position.xy - dstOrigin
 
 	dir := normalize(pos - Cursor)
 	clr := imageSrc2UnsafeAt(texCoord)

examples/shader/texel.go

@@ -20,8 +20,7 @@ package main
 
 func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 	pos := position.xy
-	origin, size := imageDstRegionOnTexture()
+	pos -= imageDstOrigin()
-	pos -= origin
+	pos /= imageDstSize()
-	pos /= size
 	return vec4(pos.x, pos.y, 0, 1)
 }

examples/shader/water.go

@@ -22,17 +22,16 @@ var Time float
 var Cursor vec2
 
 func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
-	dstOrigin, dstSize := imageDstRegionOnTexture()
+	pos := position.xy - imageDstOrigin()
-	pos := position.xy - dstOrigin
 
-	border := dstSize.y*0.6 + 4*cos(Time*3+pos.y/10)
+	border := imageDstSize().y*0.6 + 4*cos(Time*3+pos.y/10)
 	if pos.y < border {
 		return imageSrc2UnsafeAt(texCoord)
 	}
 
 	xoffset := 4 * cos(Time*3+pos.y/10)
 	yoffset := 20 * (1 + cos(Time*3+pos.y/40))
-	srcOrigin, _ := imageSrcRegionOnTexture()
+	srcOrigin := imageSrc0Origin()
 	clr := imageSrc2At(vec2(
 		texCoord.x+xoffset,
 		-(texCoord.y+yoffset-srcOrigin.y)+border*2+srcOrigin.y,

gameforui.go

@@ -29,10 +29,6 @@ const screenShaderSrc = `//kage:unit pixels
 package main
 
 func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
-	_, dr := imageDstRegionOnTexture()
-	_, sr := imageSrcRegionOnTexture()
-	scale := dr/sr
-
 	// Shift 1/512 [pixel] to avoid the tie-breaking issue.
 	pos := texCoord
 	p0 := pos - 1/2.0 + 1/512.0
@@ -49,8 +45,9 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 
 	// rate indicates how much the 4 colors are mixed. rate is in between [0, 1].
 	//
-	//     0 <= p <= 1/Scale: The rate is in between [0, 1]
+	//     0 <= p <= 1/scale: The rate is in between [0, 1]
-	//     1/Scale < p:       Don't care. Adjacent colors (e.g. c0 vs c1 in an X direction) should be the same.
+	//     1/scale < p:       Don't care. Adjacent colors (e.g. c0 vs c1 in an X direction) should be the same.
+	scale := imageDstSize()/imageSrc0Size()
 	rate := clamp(p*scale, 0, 1)
 	return mix(mix(c0, c1, rate.x), mix(c2, c3, rate.x), rate.y)
 }

image.go

@@ -737,7 +737,7 @@ var _ [len(DrawRectShaderOptions{}.Images)]struct{} = [graphics.ShaderImageCount
 // but these are invalid since texCoord is expected to be in texels in the texel-unit mode.
 // This behavior is preserved for backward compatibility. It is recommended to use the pixel-unit mode to avoid confusion.
 //
-// If no source images are specified, imageSrcRegionOnTexture returns a valid size only when the unit is pixels,
+// If no source images are specified, imageSrc0Size returns a valid size only when the unit is pixels,
 // but always returns 0 when the unit is texels (default).
 //
 // When the image i is disposed, DrawRectShader does nothing.
@@ -777,8 +777,8 @@ func (i *Image) DrawRectShader(width, height int, shader *Shader, options *DrawR
 	for i, img := range options.Images {
 		if img == nil {
 			if shader.unit == shaderir.Pixels && i == 0 {
-				// Give the source size as pixels only when the unit is pixels so that users can get the source size via imageSrcRegionOnTexture (#2166).
+				// Give the source size as pixels only when the unit is pixels so that users can get the source size via imageSrc0Size (#2166).
-				// With the texel mode, the imageSrcRegionOnTexture values should be in texels so the source position in pixels would not match.
+				// With the texel mode, the imageSrc0Origin and imageSrc0Size values should be in texels so the source position in pixels would not match.
 				srcRegions[i] = graphicsdriver.Region{
 					Width:  float32(width),
 					Height: float32(height),

internal/builtinshader/shader.go

@@ -61,7 +61,8 @@ var ColorMTranslation vec4
 
 {{if eq .Address .AddressRepeat}}
 func adjustTexelForAddressRepeat(p vec2) vec2 {
-	origin, size := imageSrcRegionOnTexture()
+	origin := imageSrc0Origin()
+	size := imageSrc0Size()
 	return mod(p - origin, size) + origin
 }
 {{end}}

internal/graphics/shader.go

@@ -23,19 +23,17 @@ import (
 )
 
 func shaderSuffix(unit shaderir.Unit) (string, error) {
-	shaderSuffix := `
+	shaderSuffix := fmt.Sprintf(`
 var __imageDstTextureSize vec2
 
 // imageSrcTextureSize returns the destination image's texture size in pixels.
 func imageDstTextureSize() vec2 {
 	return __imageDstTextureSize
 }
-`
 
-	shaderSuffix += fmt.Sprintf(`
 var __imageSrcTextureSizes [%[1]d]vec2
 
-// imageSrcTextureSize returns the source image's texture size in pixels.
+// imageSrcTextureSize returns the 0th source image's texture size in pixels.
 // As an image is a part of internal texture, the texture is usually bigger than the image.
 // The texture's size is useful when you want to calculate pixels from texels in the texel mode.
 func imageSrcTextureSize() vec2 {
@@ -52,26 +50,60 @@ var __imageDstRegionSize vec2
 // The unit is the source texture's pixel or texel.
 //
 // As an image is a part of internal texture, the image can be located at an arbitrary position on the texture.
+//
+// Deprecated: as of v2.6. Use imageDstOrigin or imageDstSize.
 func imageDstRegionOnTexture() (vec2, vec2) {
 	return __imageDstRegionOrigin, __imageDstRegionSize
 }
 
+// imageDstRegionOnTexture returns the destination image's origin on its texture.
+// The unit is the source texture's pixel or texel.
+//
+// As an image is a part of internal texture, the image can be located at an arbitrary position on the texture.
+func imageDstOrigin() vec2 {
+	return __imageDstRegionOrigin
+}
+
+// imageDstRegionOnTexture returns the destination image's size.
+// The unit is the source texture's pixel or texel.
+func imageDstSize() vec2 {
+	return __imageDstRegionSize
+}
+
 // The unit is the source texture's pixel or texel.
 var __imageSrcRegionOrigins [%[1]d]vec2
 
 // The unit is the source texture's pixel or texel.
 var __imageSrcRegionSizes [%[1]d]vec2
 
-// imageSrcRegionOnTexture returns the source image's region (the origin and the size) on its texture.
+// imageSrcRegionOnTexture returns the 0th source image's region (the origin and the size) on its texture.
 // The unit is the source texture's pixel or texel.
 //
 // As an image is a part of internal texture, the image can be located at an arbitrary position on the texture.
+//
+// Deprecated: as of v2.6. Use imageSrc0Origin or imageSrc0Size instead.
 func imageSrcRegionOnTexture() (vec2, vec2) {
 	return __imageSrcRegionOrigins[0], __imageSrcRegionSizes[0]
 }
 `, ShaderImageCount)
 
 	for i := 0; i < ShaderImageCount; i++ {
+		shaderSuffix += fmt.Sprintf(`
+// imageSrc%[1]dOrigin returns the source image's region origin on its texture.
+// The unit is the source texture's pixel or texel.
+//
+// As an image is a part of internal texture, the image can be located at an arbitrary position on the texture.
+func imageSrc%[1]dOrigin() vec2 {
+	return __imageSrcRegionOrigins[%[1]d]
+}
+
+// imageSrc%[1]dSize returns the source image's size.
+// The unit is the source texture's pixel or texel.
+func imageSrc%[1]dSize() vec2 {
+	return __imageSrcRegionSizes[%[1]d]
+}
+`, i)
+
 		pos := "pos"
 		if i >= 1 {
 			// Convert the position in texture0's positions to the target texture positions.

shader_test.go

@@ -1332,9 +1332,8 @@ package main
 
 func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 	// Adjust texCoord into [0, 1].
-	origin, size := imageSrcRegionOnTexture()
+	texCoord -= imageSrc0Origin()
-	texCoord -= origin
+	texCoord /= imageSrc0Size()
-	texCoord /= size
 	if texCoord.x >= 0.5 && texCoord.y >= 0.5 {
 		return vec4(1, 0, 0, 1)
 	}
@@ -1721,8 +1720,7 @@ func TestShaderTexelAndPixel(t *testing.T) {
 package main
 
 func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
-	orig, size := imageSrcRegionOnTexture()
+	pos := (texCoord - imageSrc0Origin()) / imageSrc0Size()
-	pos := (texCoord - orig) / size
 	pos *= vec2(%d, %d)
 	pos /= 255
 	return vec4(pos.x, pos.y, 0, 1)
@@ -1736,8 +1734,7 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 package main
 
 func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
-	orig, _ := imageSrcRegionOnTexture()
+	pos := texCoord - imageSrc0Origin()
-	pos := texCoord - orig
 	pos /= 255
 	return vec4(pos.x, pos.y, 0, 1)
 }
@@ -1835,9 +1832,8 @@ func TestShaderIVec(t *testing.T) {
 package main
 
 func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
-	orig, _ := imageSrcRegionOnTexture()
 	pos := ivec2(3, 4)
-	return imageSrc0At(vec2(pos) + orig)
+	return imageSrc0At(vec2(pos) + imageSrc0Origin())
 }
 `))
 	if err != nil {
@@ -2032,7 +2028,7 @@ package main
 func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 	t := texCoord
 
-	origin, size := imageSrcRegionOnTexture()
+	size := imageSrc0Size()
 
 	// If the unit is texels and no source images are specified, size is always 0.
 	if size == vec2(0) {
@@ -2044,7 +2040,7 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 	}
 
 	// Adjust texCoord into [0, 1].
-	t -= origin
+	t -= imageSrc0Origin()
 	if size != vec2(0) {
 		t /= size
 	}