offscreen backend now has its own type, can be used as image when drawing images

backend/backendbase/base.go

@@ -26,6 +26,9 @@ type Backend interface {
 
 	GetImageData(x, y, w, h int) *image.RGBA
 	PutImageData(img *image.RGBA, x, y int)
+
+	CanUseAsImage(b Backend) bool
+	AsImage() Image // can return nil if not supported
 }
 
 // FillStyle is the color and other details on how to fill

backend/gogl/gogl.go

@@ -42,11 +42,10 @@ type GoGLBackend struct {
 
 	ptsBuf []float32
 
-	offscreen bool
-	offscrBuf offscreenBuffer
-	offscrImg Image
-
 	glChan chan func()
+
+	activateFn                 func()
+	disableTextureRenderTarget func()
 }
 
 type offscreenBuffer struct {
@@ -70,6 +69,7 @@ func New(x, y, w, h int) (*GoGLBackend, error) {
 		fw:     float64(w),
 		fh:     float64(h),
 		ptsBuf: make([]float32, 0, 4096),
+		glChan: make(chan func()),
 	}
 
 	gl.GetError() // clear error state
@@ -211,26 +211,54 @@ func New(x, y, w, h int) (*GoGLBackend, error) {
 
 	gl.Disable(gl.SCISSOR_TEST)
 
+	b.activateFn = func() {
+		gl.BindFramebuffer(gl.FRAMEBUFFER, 0)
+		gl.Viewport(int32(b.x), int32(b.y), int32(b.w), int32(b.h))
+	}
+	b.disableTextureRenderTarget = func() {
+		gl.BindFramebuffer(gl.FRAMEBUFFER, 0)
+	}
+
 	return b, nil
 }
 
-func NewOffscreen(w, h int, alpha bool) (*GoGLBackend, error) {
+type GoGLBackendOffscreen struct {
+	GoGLBackend
+
+	offscrBuf offscreenBuffer
+	offscrImg Image
+}
+
+func NewOffscreen(w, h int, alpha bool) (*GoGLBackendOffscreen, error) {
 	b, err := New(0, 0, w, h)
 	if err != nil {
 		return nil, err
 	}
-	b.offscreen = true
+	bo := &GoGLBackendOffscreen{}
-	b.offscrBuf.alpha = alpha
+	bo.offscrBuf.alpha = alpha
-	return b, nil
+
+	b.activateFn = func() {
+		b.enableTextureRenderTarget(&bo.offscrBuf)
+		gl.Viewport(0, 0, int32(b.w), int32(b.h))
+		bo.offscrImg.w = bo.offscrBuf.w
+		bo.offscrImg.h = bo.offscrBuf.h
+		bo.offscrImg.tex = bo.offscrBuf.tex
+		bo.offscrImg.flip = true
+	}
+	b.disableTextureRenderTarget = func() {
+		b.enableTextureRenderTarget(&bo.offscrBuf)
+	}
+
+	bo.GoGLBackend = *b
+
+	return bo, nil
 }
 
 // SetBounds updates the bounds of the canvas. This would
 // usually be called for example when the window is resized
 func (b *GoGLBackend) SetBounds(x, y, w, h int) {
-	if !b.offscreen {
 	b.x, b.y = x, y
 	b.fx, b.fy = float64(x), float64(y)
-	}
 	b.w, b.h = w, h
 	b.fw, b.fh = float64(w), float64(h)
 	if b == activeContext {
@@ -239,6 +267,11 @@ func (b *GoGLBackend) SetBounds(x, y, w, h int) {
 	}
 }
 
+// SetBounds updates the size of the offscreen texture
+func (b *GoGLBackendOffscreen) SetBounds(w, h int) {
+	b.GoGLBackend.SetBounds(0, 0, w, h)
+}
+
 func (b *GoGLBackend) Size() (int, int) {
 	return b.w, b.h
 }
@@ -256,39 +289,39 @@ var activeContext *GoGLBackend
 func (b *GoGLBackend) activate() {
 	if activeContext != b {
 		activeContext = b
-		if b.offscreen {
+		b.activateFn()
-			gl.Viewport(0, 0, int32(b.w), int32(b.h))
-			b.enableTextureRenderTarget(&b.offscrBuf)
-			b.offscrImg.w = b.offscrBuf.w
-			b.offscrImg.h = b.offscrBuf.h
-			b.offscrImg.tex = b.offscrBuf.tex
-		} else {
-			gl.Viewport(int32(b.x), int32(b.y), int32(b.w), int32(b.h))
-			b.disableTextureRenderTarget()
-		}
 	}
+	b.runGLQueue()
+}
 
-loop:
+func (b *GoGLBackend) runGLQueue() {
 	for {
 		select {
 		case f := <-b.glChan:
 			f()
 		default:
-			break loop
+			return
 		}
 	}
 }
 
-func (b *GoGLBackend) DeleteOffscreen() {
+func (b *GoGLBackendOffscreen) Delete() {
-	if !b.offscreen {
-		return
-	}
 	gl.DeleteTextures(1, &b.offscrBuf.tex)
 	gl.DeleteFramebuffers(1, &b.offscrBuf.frameBuf)
 	gl.DeleteRenderbuffers(1, &b.offscrBuf.renderStencilBuf)
-	b.offscreen = false
+}
 
-	b.activate()
+func (b *GoGLBackend) CanUseAsImage(b2 backendbase.Backend) bool {
+	_, ok := b2.(*GoGLBackendOffscreen)
+	return ok
+}
+
+func (b *GoGLBackend) AsImage() backendbase.Image {
+	return nil
+}
+
+func (b *GoGLBackendOffscreen) AsImage() backendbase.Image {
+	return &b.offscrImg
 }
 
 type glColor struct {
@@ -463,14 +496,6 @@ func (b *GoGLBackend) enableTextureRenderTarget(offscr *offscreenBuffer) {
 	}
 }
 
-func (b *GoGLBackend) disableTextureRenderTarget() {
-	if b.offscreen {
-		b.enableTextureRenderTarget(&b.offscrBuf)
-	} else {
-		gl.BindFramebuffer(gl.FRAMEBUFFER, 0)
-	}
-}
-
 type vec [2]float64
 
 func (v1 vec) sub(v2 vec) vec {

backend/gogl/images.go

@@ -17,6 +17,7 @@ type Image struct {
 	tex     uint32
 	deleted bool
 	opaque  bool
+	flip    bool
 }
 
 func (b *GoGLBackend) LoadImage(src image.Image) (backendbase.Image, error) {
@@ -34,6 +35,7 @@ func (b *GoGLBackend) LoadImage(src image.Image) (backendbase.Image, error) {
 	if err != nil {
 		return nil, err
 	}
+	img.b = b
 
 	runtime.SetFinalizer(img, func(img *Image) {
 		if !img.deleted {
@@ -207,6 +209,7 @@ func (img *Image) Replace(src image.Image) error {
 	if err != nil {
 		return err
 	}
+	newImg.b = img.b
 	*img = *newImg
 	return nil
 }
@@ -225,6 +228,11 @@ func (b *GoGLBackend) DrawImage(dimg backendbase.Image, sx, sy, sw, sh float64,
 	sw /= float64(img.w)
 	sh /= float64(img.h)
 
+	if img.flip {
+		sy += sh
+		sh = -sh
+	}
+
 	var buf [16]float32
 	data := buf[:0]
 	for _, pt := range pts {

backend/xmobile/gen/gen.go

@@ -252,8 +252,8 @@ func rewriteMain(src string) string {
 		"type XMobileBackend struct {\n\tglctx gl.Context\n\n", 1)
 	src = strings.Replace(src, "func New(x, y, w, h int) (*XMobileBackend, error) {",
 		"func New(glctx gl.Context, x, y, w, h int) (*XMobileBackend, error) {", 1)
-	src = strings.Replace(src, "func NewOffscreen(w, h int, alpha bool) (*XMobileBackend, error)",
+	src = strings.Replace(src, "func NewOffscreen(w, h int, alpha bool) (*XMobileBackendOffscreen, error)",
-		"func NewOffscreen(glctx gl.Context, w, h int, alpha bool) (*XMobileBackend, error)", 1)
+		"func NewOffscreen(glctx gl.Context, w, h int, alpha bool) (*XMobileBackendOffscreen, error)", 1)
 
 	src = rewriteCalls(src, "New", func(params []string) string {
 		return "New(glctx, " + strings.Join(params, ", ") + ")"

backend/xmobile/images.go

@@ -17,6 +17,7 @@ type Image struct {
 	tex     gl.Texture
 	deleted bool
 	opaque  bool
+	flip    bool
 }
 
 func (b *XMobileBackend) LoadImage(src image.Image) (backendbase.Image, error) {
@@ -34,6 +35,7 @@ func (b *XMobileBackend) LoadImage(src image.Image) (backendbase.Image, error) {
 	if err != nil {
 		return nil, err
 	}
+	img.b = b
 
 	runtime.SetFinalizer(img, func(img *Image) {
 		if !img.deleted {
@@ -209,6 +211,7 @@ func (img *Image) Replace(src image.Image) error {
 	if err != nil {
 		return err
 	}
+	newImg.b = img.b
 	*img = *newImg
 	return nil
 }
@@ -227,6 +230,11 @@ func (b *XMobileBackend) DrawImage(dimg backendbase.Image, sx, sy, sw, sh float6
 	sw /= float64(img.w)
 	sh /= float64(img.h)
 
+	if img.flip {
+		sy += sh
+		sh = -sh
+	}
+
 	var buf [16]float32
 	data := buf[:0]
 	for _, pt := range pts {

backend/xmobile/xmobile.go

@@ -46,11 +46,10 @@ type XMobileBackend struct {
 
 	ptsBuf []float32
 
-	offscreen bool
-	offscrBuf offscreenBuffer
-	offscrImg Image
-
 	glChan chan func()
+
+	activateFn                 func()
+	disableTextureRenderTarget func()
 }
 
 type offscreenBuffer struct {
@@ -73,6 +72,7 @@ func New(glctx gl.Context, x, y, w, h int) (*XMobileBackend, error) {
 		fw:     float64(w),
 		fh:     float64(h),
 		ptsBuf: make([]float32, 0, 4096),
+		glChan: make(chan func()),
 	}
 
 	b.glctx.GetError() // clear error state
@@ -214,26 +214,54 @@ func New(glctx gl.Context, x, y, w, h int) (*XMobileBackend, error) {
 
 	b.glctx.Disable(gl.SCISSOR_TEST)
 
+	b.activateFn = func() {
+		b.glctx.BindFramebuffer(gl.FRAMEBUFFER, gl.Framebuffer{Value: 0})
+		b.glctx.Viewport(b.x, b.y, b.w, b.h)
+	}
+	b.disableTextureRenderTarget = func() {
+		b.glctx.BindFramebuffer(gl.FRAMEBUFFER, gl.Framebuffer{Value: 0})
+	}
+
 	return b, nil
 }
 
-func NewOffscreen(glctx gl.Context, w, h int, alpha bool) (*XMobileBackend, error) {
+type XMobileBackendOffscreen struct {
+	XMobileBackend
+
+	offscrBuf offscreenBuffer
+	offscrImg Image
+}
+
+func NewOffscreen(glctx gl.Context, w, h int, alpha bool) (*XMobileBackendOffscreen, error) {
 	b, err := New(glctx, 0, 0, w, h)
 	if err != nil {
 		return nil, err
 	}
-	b.offscreen = true
+	bo := &XMobileBackendOffscreen{}
-	b.offscrBuf.alpha = alpha
+	bo.offscrBuf.alpha = alpha
-	return b, nil
+
+	b.activateFn = func() {
+		b.enableTextureRenderTarget(&bo.offscrBuf)
+		b.glctx.Viewport(0, 0, b.w, b.h)
+		bo.offscrImg.w = bo.offscrBuf.w
+		bo.offscrImg.h = bo.offscrBuf.h
+		bo.offscrImg.tex = bo.offscrBuf.tex
+		bo.offscrImg.flip = true
+	}
+	b.disableTextureRenderTarget = func() {
+		b.enableTextureRenderTarget(&bo.offscrBuf)
+	}
+
+	bo.XMobileBackend = *b
+
+	return bo, nil
 }
 
 // SetBounds updates the bounds of the canvas. This would
 // usually be called for example when the window is resized
 func (b *XMobileBackend) SetBounds(x, y, w, h int) {
-	if !b.offscreen {
 	b.x, b.y = x, y
 	b.fx, b.fy = float64(x), float64(y)
-	}
 	b.w, b.h = w, h
 	b.fw, b.fh = float64(w), float64(h)
 	if b == activeContext {
@@ -242,6 +270,11 @@ func (b *XMobileBackend) SetBounds(x, y, w, h int) {
 	}
 }
 
+// SetBounds updates the size of the offscreen texture
+func (b *XMobileBackendOffscreen) SetBounds(w, h int) {
+	b.XMobileBackend.SetBounds(0, 0, w, h)
+}
+
 func (b *XMobileBackend) Size() (int, int) {
 	return b.w, b.h
 }
@@ -259,39 +292,39 @@ var activeContext *XMobileBackend
 func (b *XMobileBackend) activate() {
 	if activeContext != b {
 		activeContext = b
-		if b.offscreen {
+		b.activateFn()
-			b.glctx.Viewport(0, 0, b.w, b.h)
-			b.enableTextureRenderTarget(&b.offscrBuf)
-			b.offscrImg.w = b.offscrBuf.w
-			b.offscrImg.h = b.offscrBuf.h
-			b.offscrImg.tex = b.offscrBuf.tex
-		} else {
-			b.glctx.Viewport(b.x, b.y, b.w, b.h)
-			b.disableTextureRenderTarget()
-		}
 	}
+	b.runGLQueue()
+}
 
-loop:
+func (b *XMobileBackend) runGLQueue() {
 	for {
 		select {
 		case f := <-b.glChan:
 			f()
 		default:
-			break loop
+			return
 		}
 	}
 }
 
-func (b *XMobileBackend) DeleteOffscreen() {
+func (b *XMobileBackendOffscreen) Delete() {
-	if !b.offscreen {
-		return
-	}
 	b.glctx.DeleteTexture(b.offscrBuf.tex)
 	b.glctx.DeleteFramebuffer(b.offscrBuf.frameBuf)
 	b.glctx.DeleteRenderbuffer(b.offscrBuf.renderStencilBuf)
-	b.offscreen = false
+}
 
-	b.activate()
+func (b *XMobileBackend) CanUseAsImage(b2 backendbase.Backend) bool {
+	_, ok := b2.(*XMobileBackendOffscreen)
+	return ok
+}
+
+func (b *XMobileBackend) AsImage() backendbase.Image {
+	return nil
+}
+
+func (b *XMobileBackendOffscreen) AsImage() backendbase.Image {
+	return &b.offscrImg
 }
 
 type glColor struct {
@@ -466,14 +499,6 @@ func (b *XMobileBackend) enableTextureRenderTarget(offscr *offscreenBuffer) {
 	}
 }
 
-func (b *XMobileBackend) disableTextureRenderTarget() {
-	if b.offscreen {
-		b.enableTextureRenderTarget(&b.offscrBuf)
-	} else {
-		b.glctx.BindFramebuffer(gl.FRAMEBUFFER, gl.Framebuffer{Value: 0})
-	}
-}
-
 type vec [2]float64
 
 func (v1 vec) sub(v2 vec) vec {

canvas.go

@@ -20,9 +20,6 @@ import (
 type Canvas struct {
 	b backendbase.Backend
 
-	w, h   int
-	fw, fh float64
-
 	path   Path2D
 	convex bool
 	rect   bool
@@ -138,8 +135,6 @@ func New(backend backendbase.Backend) *Canvas {
 		stateStack: make([]drawState, 0, 20),
 		images:     make(map[interface{}]*Image),
 	}
-	w, h := backend.Size()
-	cv.setBounds(w, h)
 	cv.state.lineWidth = 1
 	cv.state.lineAlpha = 1
 	cv.state.miterLimitSqr = 100
@@ -150,19 +145,20 @@ func New(backend backendbase.Backend) *Canvas {
 	return cv
 }
 
-func (cv *Canvas) setBounds(w, h int) {
+// Width returns the internal width of the canvas
-	cv.w, cv.h = w, h
+func (cv *Canvas) Width() int {
-	cv.fw, cv.fh = float64(w), float64(h)
+	w, _ := cv.b.Size()
+	return w
 }
 
-// Width returns the internal width of the canvas
-func (cv *Canvas) Width() int { return cv.w }
-
 // Height returns the internal height of the canvas
-func (cv *Canvas) Height() int { return cv.h }
+func (cv *Canvas) Height() int {
+	_, h := cv.b.Size()
+	return h
+}
 
 // Size returns the internal width and height of the canvas
-func (cv *Canvas) Size() (int, int) { return cv.w, cv.h }
+func (cv *Canvas) Size() (int, int) { return cv.b.Size() }
 
 func (cv *Canvas) tf(v vec) vec {
 	v, _ = v.mulMat(cv.state.transform)

images.go

@@ -42,7 +42,8 @@ func (cv *Canvas) LoadImage(src interface{}) (*Image, error) {
 			return nil, err
 		}
 	case *Canvas:
-		src = cv.GetImageData(0, 0, cv.Width(), cv.Height())
+		w, h := cv.b.Size()
+		src = cv.GetImageData(0, 0, w, h)
 	default:
 		return nil, errors.New("Unsupported source type")
 	}
@@ -82,6 +83,19 @@ func (cv *Canvas) getImage(src interface{}) *Image {
 		}
 		cv.images[v] = img
 		return img
+	case *Canvas:
+		if !cv.b.CanUseAsImage(v.b) {
+			w, h := v.Size()
+			return cv.getImage(v.GetImageData(0, 0, w, h))
+		}
+		bimg := v.b.AsImage()
+		if bimg == nil {
+			w, h := v.Size()
+			return cv.getImage(v.GetImageData(0, 0, w, h))
+		}
+		img := &Image{cv: cv, img: bimg}
+		cv.images[v] = img
+		return img
 	}
 	fmt.Fprintf(os.Stderr, "Unknown image type: %T\n", src)
 	cv.images[src] = nil

text.go

@@ -96,14 +96,17 @@ func (cv *Canvas) FillText(str string, x, y float64) {
 			curX += float64(kern) / 64
 		}
 
+		w, h := cv.b.Size()
+		fw, fh := float64(w), float64(h)
+
 		p0 := cv.tf(vec{float64(bounds.Min.X) + curX, float64(bounds.Min.Y) + y})
 		p1 := cv.tf(vec{float64(bounds.Min.X) + curX, float64(bounds.Max.Y) + y})
 		p2 := cv.tf(vec{float64(bounds.Max.X) + curX, float64(bounds.Max.Y) + y})
 		p3 := cv.tf(vec{float64(bounds.Max.X) + curX, float64(bounds.Min.Y) + y})
 		inside := (p0[0] >= 0 || p1[0] >= 0 || p2[0] >= 0 || p3[0] >= 0) &&
 			(p0[1] >= 0 || p1[1] >= 0 || p2[1] >= 0 || p3[1] >= 0) &&
-			(p0[0] < cv.fw || p1[0] < cv.fw || p2[0] < cv.fw || p3[0] < cv.fw) &&
+			(p0[0] < fw || p1[0] < fw || p2[0] < fw || p3[0] < fw) &&
-			(p0[1] < cv.fh || p1[1] < cv.fh || p2[1] < cv.fh || p3[1] < cv.fh)
+			(p0[1] < fh || p1[1] < fh || p2[1] < fh || p3[1] < fh)
 
 		if !curInside && inside {
 			curInside = true