implemented image pattern transformation

backend/backendbase/base.go

@@ -108,6 +108,7 @@ type Image interface {
 
 type ImagePatternData struct {
 	Image     Image
+	Transform [9]float64
 }
 
 type ImagePattern interface {

backend/gogl/gogl.go

@@ -432,13 +432,19 @@ func (b *GoGLBackend) useShader(style *backendbase.FillStyle) (vertexLoc uint32)
 		return b.rgr.Vertex
 	}
 	if ip := style.ImagePattern; ip != nil {
-		img := ip.(*ImagePattern).data.Image.(*Image)
+		ipd := ip.(*ImagePattern).data
+		img := ipd.Image.(*Image)
 		gl.UseProgram(b.ipr.ID)
 		gl.ActiveTexture(gl.TEXTURE0)
 		gl.BindTexture(gl.TEXTURE_2D, img.tex)
 		gl.Uniform2f(b.ipr.CanvasSize, float32(b.fw), float32(b.fh))
 		gl.Uniform2f(b.ipr.ImageSize, float32(img.w), float32(img.h))
 		gl.Uniform1i(b.ipr.Image, 0)
+		var f32mat [9]float32
+		for i, v := range ipd.Transform {
+			f32mat[i] = float32(v)
+		}
+		gl.UniformMatrix3fv(b.ipr.ImageTransform, 1, false, &f32mat[0])
 		gl.Uniform1f(b.ipr.GlobalAlpha, float32(style.Color.A)/255)
 		return b.ipr.Vertex
 	}
@@ -489,13 +495,19 @@ func (b *GoGLBackend) useAlphaShader(style *backendbase.FillStyle, alphaTexSlot
 		return b.rgar.Vertex, b.rgar.AlphaTexCoord
 	}
 	if ip := style.ImagePattern; ip != nil {
-		img := ip.(*ImagePattern).data.Image.(*Image)
+		ipd := ip.(*ImagePattern).data
+		img := ipd.Image.(*Image)
 		gl.UseProgram(b.ipar.ID)
 		gl.ActiveTexture(gl.TEXTURE0)
 		gl.BindTexture(gl.TEXTURE_2D, img.tex)
 		gl.Uniform2f(b.ipar.CanvasSize, float32(b.fw), float32(b.fh))
 		gl.Uniform2f(b.ipar.ImageSize, float32(img.w), float32(img.h))
 		gl.Uniform1i(b.ipar.Image, 0)
+		var f32mat [9]float32
+		for i, v := range ipd.Transform {
+			f32mat[i] = float32(v)
+		}
+		gl.UniformMatrix3fv(b.ipr.ImageTransform, 1, false, &f32mat[0])
 		gl.Uniform1i(b.ipar.AlphaTex, alphaTexSlot)
 		gl.Uniform1f(b.ipar.GlobalAlpha, float32(style.Color.A)/255)
 		return b.ipar.Vertex, b.ipar.AlphaTexCoord

backend/gogl/shaders.go

@@ -132,9 +132,11 @@ precision mediump float;
 varying vec2 v_cp;
 uniform vec2 imageSize;
 uniform sampler2D image;
+uniform mat3 imageTransform;
 uniform float globalAlpha;
 void main() {
-	vec4 col = texture2D(image, mod(v_cp / imageSize, 1.0));
+	vec3 tfp = vec3(v_cp, 1.0) * imageTransform;
+	vec4 col = texture2D(image, mod(tfp.xy / imageSize, 1.0));
 	col.a *= globalAlpha;
     gl_FragColor = col;
 }`
@@ -259,10 +261,12 @@ varying vec2 v_cp;
 varying vec2 v_atc;
 uniform vec2 imageSize;
 uniform sampler2D image;
+uniform mat3 imageTransform;
 uniform sampler2D alphaTex;
 uniform float globalAlpha;
 void main() {
-    vec4 col = texture2D(image, mod(v_cp / imageSize, 1.0));
+	vec3 tfp = vec3(v_cp, 1.0) * imageTransform;
+	vec4 col = texture2D(image, mod(tfp.xy / imageSize, 1.0));
     col.a *= texture2D(alphaTex, v_atc).a * globalAlpha;
 	gl_FragColor = col;
 }`
@@ -404,6 +408,7 @@ type imagePatternShader struct {
 	CanvasSize     int32
 	ImageSize      int32
 	Image          int32
+	ImageTransform int32
 	GlobalAlpha    int32
 }
 
@@ -451,6 +456,7 @@ type imagePatternAlphaShader struct {
 	CanvasSize     int32
 	ImageSize      int32
 	Image          int32
+	ImageTransform int32
 	AlphaTex       int32
 	GlobalAlpha    int32
 }

images.go

@@ -189,15 +189,29 @@ func (cv *Canvas) PutImageData(img *image.RGBA, x, y int) {
 type ImagePattern struct {
 	cv  *Canvas
 	img *Image
+	tf  [9]float64
 	ip  backendbase.ImagePattern
 }
 
 func (ip *ImagePattern) data() backendbase.ImagePatternData {
 	return backendbase.ImagePatternData{
 		Image:     ip.img.img,
+		Transform: ip.tf,
 	}
 }
 
+// SetTransform changes the transformation of the image pattern
+// to the given matrix. The matrix is a 3x3 matrix, but three
+// of the values are always identity values
+func (ip *ImagePattern) SetTransform(tf [6]float64) {
+	ip.tf = [9]float64{
+		tf[0], tf[1], 0,
+		tf[2], tf[3], 0,
+		tf[4], tf[5], 1,
+	}
+	ip.ip.Replace(ip.data())
+}
+
 // CreatePattern creates a new image pattern with the specified
 // image and repetition
 func (cv *Canvas) CreatePattern(src interface{}, repetition string) *ImagePattern {