ebiten: Add a new shader function imageDstRegionOnTexture

Updates #1428

internal/graphics/vertex.go

@@ -25,15 +25,19 @@ const (
 	// Any shaders in Ebiten must have these uniform variables.
 	PreservedUniformVariablesNum = 1 + // the destination texture size
 		1 + // the texture sizes array
+		1 + // the texture destination region's origin
+		1 + // the texture destination region's size
 		1 + // the offsets array of the second and the following images
 		1 + // the texture source region's origin
 		1 // the texture source region's size
 
-	DestinationTextureSizeUniformVariableIndex    = 0
-	TextureSizesUniformVariableIndex              = 1
-	TextureSourceOffsetsUniformVariableIndex      = 2
-	TextureSourceRegionOriginUniformVariableIndex = 3
-	TextureSourceRegionSizeUniformVariableIndex   = 4
+	DestinationTextureSizeUniformVariableIndex         = 0
+	TextureSizesUniformVariableIndex                   = 1
+	TextureDestinationRegionOriginUniformVariableIndex = 2
+	TextureDestinationRegionSizeUniformVariableIndex   = 3
+	TextureSourceOffsetsUniformVariableIndex           = 4
+	TextureSourceRegionOriginUniformVariableIndex      = 5
+	TextureSourceRegionSizeUniformVariableIndex        = 6
 )
 
 const (

internal/graphicsdriver/metal/graphics.go

@@ -970,6 +970,14 @@ func (g *Graphics) DrawShader(dstID driver.ImageID, srcIDs [graphics.ShaderImage
 	}
 	us[graphics.TextureSizesUniformVariableIndex] = usizes
 
+	// Set the destination region's origin.
+	udorigin := []float32{float32(dstRegion.X) / float32(dw), float32(dstRegion.Y) / float32(dh)}
+	us[graphics.TextureDestinationRegionOriginUniformVariableIndex] = udorigin
+
+	// Set the destination region's size.
+	udsize := []float32{float32(dstRegion.Width) / float32(dw), float32(dstRegion.Height) / float32(dh)}
+	us[graphics.TextureDestinationRegionSizeUniformVariableIndex] = udsize
+
 	// Set the source offsets.
 	uoffsets := make([]float32, 2*len(offsets))
 	for i, offset := range offsets {
@@ -979,8 +987,8 @@ func (g *Graphics) DrawShader(dstID driver.ImageID, srcIDs [graphics.ShaderImage
 	us[graphics.TextureSourceOffsetsUniformVariableIndex] = uoffsets
 
 	// Set the source region's origin of texture0.
-	uorigin := []float32{float32(srcRegion.X), float32(srcRegion.Y)}
-	us[graphics.TextureSourceRegionOriginUniformVariableIndex] = uorigin
+	usorigin := []float32{float32(srcRegion.X), float32(srcRegion.Y)}
+	us[graphics.TextureSourceRegionOriginUniformVariableIndex] = usorigin
 
 	// Set the source region's size of texture0.
 	ussize := []float32{float32(srcRegion.Width), float32(srcRegion.Height)}

internal/graphicsdriver/opengl/graphics.go

@@ -341,6 +341,21 @@ func (g *Graphics) DrawShader(dst driver.ImageID, srcs [graphics.ShaderImageNum]
 		us[idx].value = sizes
 		us[idx].typ = s.ir.Uniforms[idx]
 	}
+	dw, dh := d.framebufferSize()
+	{
+		origin := []float32{float32(dstRegion.X) / float32(dw), float32(dstRegion.Y) / float32(dh)}
+		const idx = graphics.TextureDestinationRegionOriginUniformVariableIndex
+		us[idx].name = fmt.Sprintf("U%d", idx)
+		us[idx].value = origin
+		us[idx].typ = s.ir.Uniforms[idx]
+	}
+	{
+		size := []float32{float32(dstRegion.Width) / float32(dw), float32(dstRegion.Height) / float32(dh)}
+		const idx = graphics.TextureDestinationRegionSizeUniformVariableIndex
+		us[idx].name = fmt.Sprintf("U%d", idx)
+		us[idx].value = size
+		us[idx].typ = s.ir.Uniforms[idx]
+	}
 	{
 		voffsets := make([]float32, 2*len(offsets))
 		for i, o := range offsets {

shader.go

@@ -49,6 +49,20 @@ func imageSrcTextureSize() vec2 {
 	return __textureSizes[0]
 }
 
+// The unit is the source texture's texel.
+var __textureDestinationRegionOrigin vec2
+
+// The unit is the source texture's texel.
+var __textureDestinationRegionSize vec2
+
+// imageDstRegionOnTexture returns the destination image's region (the origin and the size) on its texture.
+// The unit is the source texture's texel.
+//
+// As an image is a part of internal texture, the image can be located at an arbitrary position on the texture.
+func imageDstRegionOnTexture() (vec2, vec2) {
+	return __textureDestinationRegionOrigin, __textureDestinationRegionSize
+}
+
 // The unit is the source texture's texel.
 var __textureSourceOffsets [%[2]d]vec2