performance optimization, avoid use of stencil buffer when drawing with opaque styles

canvas.go

@@ -360,6 +360,19 @@ func parseStyle(value ...interface{}) drawStyle {
 	return style
 }
 
+func (s *drawStyle) isOpaque() bool {
+	if lg := s.linearGradient; lg != nil {
+		return lg.opaque
+	}
+	if rg := s.radialGradient; rg != nil {
+		return rg.opaque
+	}
+	if img := s.image; img != nil {
+		return img.opaque
+	}
+	return s.color.a >= 1
+}
+
 func (cv *Canvas) useShader(style *drawStyle) (vertexLoc uint32) {
 	if lg := style.linearGradient; lg != nil {
 		lg.load()

gradients.go

@@ -28,6 +28,7 @@ type gradient struct {
 	tex      uint32
 	loaded   bool
 	deleted  bool
+	opaque   bool
 }
 
 type gradientStop struct {
@@ -39,7 +40,7 @@ type gradientStop struct {
 // the coordinates from where to where the gradient
 // will apply on the canvas
 func NewLinearGradient(x0, y0, x1, y1 float64) *LinearGradient {
-	lg := &LinearGradient{gradient: gradient{from: vec{x0, y0}, to: vec{x1, y1}}}
+	lg := &LinearGradient{gradient: gradient{from: vec{x0, y0}, to: vec{x1, y1}, opaque: true}}
 	gli.GenTextures(1, &lg.tex)
 	gli.ActiveTexture(gl_TEXTURE0)
 	gli.BindTexture(gl_TEXTURE_2D, lg.tex)
@@ -60,7 +61,7 @@ func NewLinearGradient(x0, y0, x1, y1 float64) *LinearGradient {
 // gradient will apply from the first to the second
 // circle
 func NewRadialGradient(x0, y0, r0, x1, y1, r1 float64) *RadialGradient {
-	rg := &RadialGradient{gradient: gradient{from: vec{x0, y0}, to: vec{x1, y1}}, radFrom: r0, radTo: r1}
+	rg := &RadialGradient{gradient: gradient{from: vec{x0, y0}, to: vec{x1, y1}, opaque: true}, radFrom: r0, radTo: r1}
 	gli.GenTextures(1, &rg.tex)
 	gli.ActiveTexture(gl_TEXTURE0)
 	gli.BindTexture(gl_TEXTURE_2D, rg.tex)
@@ -137,6 +138,9 @@ func (g *gradient) colorAt(pos float64) glColor {
 // right place
 func (g *gradient) AddColorStop(pos float64, color ...interface{}) {
 	c, _ := parseColor(color...)
+	if c.a < 1 {
+		g.opaque = false
+	}
 	insert := len(g.stops)
 	for i, stop := range g.stops {
 		if stop.pos > pos {

images.go

@@ -14,6 +14,7 @@ type Image struct {
 	w, h    int
 	tex     uint32
 	deleted bool
+	opaque  bool
 }
 
 var images = make(map[string]*Image)
@@ -89,7 +90,20 @@ func getImage(image interface{}) *Image {
 }
 
 func loadImageRGBA(src *image.RGBA) (*Image, error) {
-	img := &Image{w: src.Bounds().Dx(), h: src.Bounds().Dy()}
+	img := &Image{w: src.Bounds().Dx(), h: src.Bounds().Dy(), opaque: true}
+
+checkOpaque:
+	for y := 0; y < img.h; y++ {
+		off := src.PixOffset(0, y) + 3
+		for x := 0; x < img.w; x++ {
+			if src.Pix[off] < 255 {
+				img.opaque = false
+				break checkOpaque
+			}
+			off += 4
+		}
+	}
+
 	gli.GenTextures(1, &img.tex)
 	gli.ActiveTexture(gl_TEXTURE0)
 	gli.BindTexture(gl_TEXTURE_2D, img.tex)
@@ -155,7 +169,7 @@ func loadImageGray(src *image.Gray) (*Image, error) {
 }
 
 func loadImageConverted(src image.Image) (*Image, error) {
-	img := &Image{w: src.Bounds().Dx(), h: src.Bounds().Dy()}
+	img := &Image{w: src.Bounds().Dx(), h: src.Bounds().Dy(), opaque: true}
 	gli.GenTextures(1, &img.tex)
 	gli.ActiveTexture(gl_TEXTURE0)
 	gli.BindTexture(gl_TEXTURE_2D, img.tex)
@@ -172,6 +186,9 @@ func loadImageConverted(src image.Image) (*Image, error) {
 			ir, ig, ib, ia := src.At(x, y).RGBA()
 			r, g, b, a := uint8(ir>>8), uint8(ig>>8), uint8(ib>>8), uint8(ia>>8)
 			data = append(data, r, g, b, a)
+			if a < 255 {
+				img.opaque = false
+			}
 		}
 	}
 	gli.TexImage2D(gl_TEXTURE_2D, 0, gl_RGBA, int32(img.w), int32(img.h), 0, gl_RGBA, gl_UNSIGNED_BYTE, gli.Ptr(&data[0]))

paths.go

@@ -364,41 +364,50 @@ func (cv *Canvas) stroke(path []pathPoint) {
 
 	gli.BindBuffer(gl_ARRAY_BUFFER, buf)
 
-	gli.ColorMask(false, false, false, false)
+	if cv.state.globalAlpha >= 1 && cv.state.lineAlpha >= 1 && cv.state.stroke.isOpaque() {
-	gli.StencilFunc(gl_ALWAYS, 1, 0xFF)
+		vertex := cv.useShader(&cv.state.stroke)
-	gli.StencilOp(gl_REPLACE, gl_REPLACE, gl_REPLACE)
-	gli.StencilMask(0x01)
 
-	gli.UseProgram(sr.id)
+		gli.EnableVertexAttribArray(vertex)
-	gli.Uniform4f(sr.color, 0, 0, 0, 0)
+		gli.VertexAttribPointer(vertex, 2, gl_FLOAT, false, 0, 0)
-	gli.Uniform2f(sr.canvasSize, float32(cv.fw), float32(cv.fh))
+		gli.DrawArrays(gl_TRIANGLES, 6, int32(len(tris)/2-6))
+		gli.DisableVertexAttribArray(vertex)
+	} else {
+		gli.ColorMask(false, false, false, false)
+		gli.StencilFunc(gl_ALWAYS, 1, 0xFF)
+		gli.StencilOp(gl_REPLACE, gl_REPLACE, gl_REPLACE)
+		gli.StencilMask(0x01)
 
-	gli.EnableVertexAttribArray(sr.vertex)
+		gli.UseProgram(sr.id)
-	gli.VertexAttribPointer(sr.vertex, 2, gl_FLOAT, false, 0, 0)
+		gli.Uniform4f(sr.color, 0, 0, 0, 0)
-	gli.DrawArrays(gl_TRIANGLES, 6, int32(len(tris)/2-6))
+		gli.Uniform2f(sr.canvasSize, float32(cv.fw), float32(cv.fh))
-	gli.DisableVertexAttribArray(sr.vertex)
 
-	gli.ColorMask(true, true, true, true)
+		gli.EnableVertexAttribArray(sr.vertex)
+		gli.VertexAttribPointer(sr.vertex, 2, gl_FLOAT, false, 0, 0)
+		gli.DrawArrays(gl_TRIANGLES, 6, int32(len(tris)/2-6))
+		gli.DisableVertexAttribArray(sr.vertex)
 
-	gli.StencilFunc(gl_EQUAL, 1, 0xFF)
+		gli.ColorMask(true, true, true, true)
 
-	origAlpha := cv.state.globalAlpha
+		gli.StencilFunc(gl_EQUAL, 1, 0xFF)
-	if cv.state.lineAlpha < 1 {
+
-		cv.state.globalAlpha *= cv.state.lineAlpha
+		origAlpha := cv.state.globalAlpha
+		if cv.state.lineAlpha < 1 {
+			cv.state.globalAlpha *= cv.state.lineAlpha
+		}
+		vertex := cv.useShader(&cv.state.stroke)
+		cv.state.globalAlpha = origAlpha
+
+		gli.EnableVertexAttribArray(vertex)
+		gli.VertexAttribPointer(vertex, 2, gl_FLOAT, false, 0, 0)
+		gli.DrawArrays(gl_TRIANGLES, 0, 6)
+		gli.DisableVertexAttribArray(vertex)
+
+		gli.StencilOp(gl_KEEP, gl_KEEP, gl_KEEP)
+		gli.StencilFunc(gl_ALWAYS, 0, 0xFF)
+
+		gli.Clear(gl_STENCIL_BUFFER_BIT)
+		gli.StencilMask(0xFF)
 	}
-	vertex := cv.useShader(&cv.state.stroke)
-	cv.state.globalAlpha = origAlpha
-
-	gli.EnableVertexAttribArray(vertex)
-	gli.VertexAttribPointer(vertex, 2, gl_FLOAT, false, 0, 0)
-	gli.DrawArrays(gl_TRIANGLES, 0, 6)
-	gli.DisableVertexAttribArray(vertex)
-
-	gli.StencilOp(gl_KEEP, gl_KEEP, gl_KEEP)
-	gli.StencilFunc(gl_ALWAYS, 0, 0xFF)
-
-	gli.Clear(gl_STENCIL_BUFFER_BIT)
-	gli.StencilMask(0xFF)
 }
 
 func (cv *Canvas) lineJoint(p pathPoint, p0, p1, p2, l0p0, l0p1, l0p2, l0p3 vec, tris []float32) []float32 {
@@ -521,35 +530,44 @@ func (cv *Canvas) Fill() {
 
 	gli.BindBuffer(gl_ARRAY_BUFFER, buf)
 
-	gli.ColorMask(false, false, false, false)
+	if cv.state.globalAlpha >= 1 && cv.state.lineAlpha >= 1 && cv.state.fill.isOpaque() {
-	gli.StencilFunc(gl_ALWAYS, 1, 0xFF)
+		vertex := cv.useShader(&cv.state.fill)
-	gli.StencilOp(gl_REPLACE, gl_REPLACE, gl_REPLACE)
-	gli.StencilMask(0x01)
 
-	gli.UseProgram(sr.id)
+		gli.EnableVertexAttribArray(vertex)
-	gli.Uniform4f(sr.color, 0, 0, 0, 0)
+		gli.VertexAttribPointer(vertex, 2, gl_FLOAT, false, 0, 0)
-	gli.Uniform2f(sr.canvasSize, float32(cv.fw), float32(cv.fh))
+		gli.DrawArrays(gl_TRIANGLES, 6, int32(len(tris)/2-6))
+		gli.DisableVertexAttribArray(vertex)
+	} else {
+		gli.ColorMask(false, false, false, false)
+		gli.StencilFunc(gl_ALWAYS, 1, 0xFF)
+		gli.StencilOp(gl_REPLACE, gl_REPLACE, gl_REPLACE)
+		gli.StencilMask(0x01)
 
-	gli.EnableVertexAttribArray(sr.vertex)
+		gli.UseProgram(sr.id)
-	gli.VertexAttribPointer(sr.vertex, 2, gl_FLOAT, false, 0, 0)
+		gli.Uniform4f(sr.color, 0, 0, 0, 0)
-	gli.DrawArrays(gl_TRIANGLES, 6, int32(len(tris)/2-6))
+		gli.Uniform2f(sr.canvasSize, float32(cv.fw), float32(cv.fh))
-	gli.DisableVertexAttribArray(sr.vertex)
 
-	gli.ColorMask(true, true, true, true)
+		gli.EnableVertexAttribArray(sr.vertex)
+		gli.VertexAttribPointer(sr.vertex, 2, gl_FLOAT, false, 0, 0)
+		gli.DrawArrays(gl_TRIANGLES, 6, int32(len(tris)/2-6))
+		gli.DisableVertexAttribArray(sr.vertex)
 
-	gli.StencilFunc(gl_EQUAL, 1, 0xFF)
+		gli.ColorMask(true, true, true, true)
 
-	vertex := cv.useShader(&cv.state.fill)
+		gli.StencilFunc(gl_EQUAL, 1, 0xFF)
-	gli.EnableVertexAttribArray(vertex)
-	gli.VertexAttribPointer(vertex, 2, gl_FLOAT, false, 0, 0)
-	gli.DrawArrays(gl_TRIANGLES, 0, 6)
-	gli.DisableVertexAttribArray(vertex)
 
-	gli.StencilOp(gl_KEEP, gl_KEEP, gl_KEEP)
+		vertex := cv.useShader(&cv.state.fill)
-	gli.StencilFunc(gl_ALWAYS, 0, 0xFF)
+		gli.EnableVertexAttribArray(vertex)
+		gli.VertexAttribPointer(vertex, 2, gl_FLOAT, false, 0, 0)
+		gli.DrawArrays(gl_TRIANGLES, 0, 6)
+		gli.DisableVertexAttribArray(vertex)
 
-	gli.Clear(gl_STENCIL_BUFFER_BIT)
+		gli.StencilOp(gl_KEEP, gl_KEEP, gl_KEEP)
-	gli.StencilMask(0xFF)
+		gli.StencilFunc(gl_ALWAYS, 0, 0xFF)
+
+		gli.Clear(gl_STENCIL_BUFFER_BIT)
+		gli.StencilMask(0xFF)
+	}
 }
 
 func (cv *Canvas) appendSubPathTriangles(tris []float32, path []pathPoint) []float32 {