added a function to switch to an offscreen framebuffer

canvas.go

@@ -177,20 +177,25 @@ loop:
 const alphaTexSize = 2048
 
 var (
-	gli       GL
+	gli              GL
-	buf       uint32
+	buf              uint32
-	shadowBuf uint32
+	shadowBuf        uint32
-	alphaTex  uint32
+	alphaTex         uint32
-	sr        *solidShader
+	sr               *solidShader
-	lgr       *linearGradientShader
+	lgr              *linearGradientShader
-	rgr       *radialGradientShader
+	rgr              *radialGradientShader
-	ipr       *imagePatternShader
+	ipr              *imagePatternShader
-	sar       *solidAlphaShader
+	sar              *solidAlphaShader
-	rgar      *radialGradientAlphaShader
+	rgar             *radialGradientAlphaShader
-	lgar      *linearGradientAlphaShader
+	lgar             *linearGradientAlphaShader
-	ipar      *imagePatternAlphaShader
+	ipar             *imagePatternAlphaShader
-	ir        *imageShader
+	ir               *imageShader
-	glChan    = make(chan func())
+	offScrTex        uint32
+	offScrW          int
+	offScrH          int
+	renderStencilBuf uint32
+	frameBuf         uint32
+	glChan           = make(chan func())
 )
 
 // LoadGL needs to be called once per GL context to load the GL assets
@@ -509,6 +514,53 @@ func (cv *Canvas) useAlphaShader(style *drawStyle, alphaTexSlot int32) (vertexLo
 	return sar.vertex, sar.alphaTexCoord
 }
 
+func (cv *Canvas) enableTextureRenderTarget() {
+	if offScrW != cv.w || offScrH != cv.h {
+		if offScrW != 0 && offScrH != 0 {
+			gli.DeleteTextures(1, &offScrTex)
+			gli.DeleteFramebuffers(1, &frameBuf)
+			gli.DeleteRenderbuffers(1, &renderStencilBuf)
+		}
+		offScrW = cv.w
+		offScrH = cv.h
+
+		gli.GenTextures(1, &offScrTex)
+		gli.BindTexture(gl_TEXTURE_2D, offScrTex)
+		// todo do non-power-of-two textures work everywhere?
+		gli.TexImage2D(gl_TEXTURE_2D, 0, gl_RGB, int32(cv.w), int32(cv.h), 0, gl_RGB, gl_UNSIGNED_BYTE, nil)
+		gli.TexParameteri(gl_TEXTURE_2D, gl_TEXTURE_MAG_FILTER, gl_NEAREST)
+		gli.TexParameteri(gl_TEXTURE_2D, gl_TEXTURE_MIN_FILTER, gl_NEAREST)
+
+		gli.GenFramebuffers(1, &frameBuf)
+		gli.BindFramebuffer(gl_FRAMEBUFFER, frameBuf)
+
+		gli.GenRenderbuffers(1, &renderStencilBuf)
+		gli.BindRenderbuffer(gl_RENDERBUFFER, renderStencilBuf)
+		gli.RenderbufferStorage(gl_RENDERBUFFER, gl_DEPTH_STENCIL, int32(cv.w), int32(cv.h))
+		gli.FramebufferRenderbuffer(gl_FRAMEBUFFER, gl_DEPTH_STENCIL_ATTACHMENT, gl_RENDERBUFFER, renderStencilBuf)
+
+		gli.FramebufferTexture(gl_FRAMEBUFFER, gl_COLOR_ATTACHMENT0, offScrTex, 0)
+
+		if gli.CheckFramebufferStatus(gl_FRAMEBUFFER) != gl_FRAMEBUFFER_COMPLETE {
+			// todo this should maybe not panic
+			panic("Failed to set up framebuffer for offscreen texture")
+		}
+
+		gli.Clear(gl_COLOR_BUFFER_BIT | gl_STENCIL_BUFFER_BIT)
+	} else {
+		gli.BindFramebuffer(gl_FRAMEBUFFER, frameBuf)
+	}
+}
+
+func (cv *Canvas) disableTextureRenderTarget() {
+	gli.BindFramebuffer(gl_FRAMEBUFFER, 0)
+}
+
+func (cv *Canvas) renderOffscreenTexture() {
+	img := Image{w: cv.w, h: cv.h, tex: offScrTex}
+	cv.DrawImage(&img, 0, 0, cv.fw, cv.fh)
+}
+
 // SetLineWidth sets the line width for any line drawing calls
 func (cv *Canvas) SetLineWidth(width float64) {
 	if width < 0 {

glimpl/gogl/goglimpl.go

@@ -24,6 +24,12 @@ func (_ GLImpl) AttachShader(program uint32, shader uint32) {
 func (_ GLImpl) BindBuffer(target uint32, buffer uint32) {
 	gl.BindBuffer(target, buffer)
 }
+func (_ GLImpl) BindFramebuffer(target uint32, framebuffer uint32) {
+	gl.BindFramebuffer(target, framebuffer)
+}
+func (_ GLImpl) BindRenderbuffer(target uint32, renderbuffer uint32) {
+	gl.BindRenderbuffer(target, renderbuffer)
+}
 func (_ GLImpl) BindTexture(target uint32, texture uint32) {
 	gl.BindTexture(target, texture)
 }
@@ -33,6 +39,9 @@ func (_ GLImpl) BlendFunc(sfactor uint32, dfactor uint32) {
 func (_ GLImpl) BufferData(target uint32, size int, data unsafe.Pointer, usage uint32) {
 	gl.BufferData(target, size, data, usage)
 }
+func (_ GLImpl) CheckFramebufferStatus(target uint32) uint32 {
+	return gl.CheckFramebufferStatus(target)
+}
 func (_ GLImpl) Clear(mask uint32) {
 	gl.Clear(mask)
 }
@@ -54,6 +63,12 @@ func (_ GLImpl) CreateShader(xtype uint32) uint32 {
 func (_ GLImpl) DeleteShader(shader uint32) {
 	gl.DeleteShader(shader)
 }
+func (_ GLImpl) DeleteFramebuffers(n int32, framebuffers *uint32) {
+	gl.DeleteFramebuffers(n, framebuffers)
+}
+func (_ GLImpl) DeleteRenderbuffers(n int32, renderbuffers *uint32) {
+	gl.DeleteRenderbuffers(n, renderbuffers)
+}
 func (_ GLImpl) DeleteTextures(n int32, textures *uint32) {
 	gl.DeleteTextures(n, textures)
 }
@@ -72,9 +87,21 @@ func (_ GLImpl) Enable(cap uint32) {
 func (_ GLImpl) EnableVertexAttribArray(index uint32) {
 	gl.EnableVertexAttribArray(index)
 }
+func (_ GLImpl) FramebufferRenderbuffer(target uint32, attachment uint32, renderbuffertarget uint32, renderbuffer uint32) {
+	gl.FramebufferRenderbuffer(target, attachment, renderbuffertarget, renderbuffer)
+}
+func (_ GLImpl) FramebufferTexture(target uint32, attachment uint32, texture uint32, level int32) {
+	gl.FramebufferTexture(target, attachment, texture, level)
+}
 func (_ GLImpl) GenBuffers(n int32, buffers *uint32) {
 	gl.GenBuffers(n, buffers)
 }
+func (_ GLImpl) GenFramebuffers(n int32, framebuffers *uint32) {
+	gl.GenFramebuffers(n, framebuffers)
+}
+func (_ GLImpl) GenRenderbuffers(n int32, renderbuffers *uint32) {
+	gl.GenRenderbuffers(n, renderbuffers)
+}
 func (_ GLImpl) GenTextures(n int32, textures *uint32) {
 	gl.GenTextures(n, textures)
 }
@@ -119,6 +146,9 @@ func (_ GLImpl) GetUniformLocation(program uint32, name string) int32 {
 func (_ GLImpl) LinkProgram(program uint32) {
 	gl.LinkProgram(program)
 }
+func (_ GLImpl) RenderbufferStorage(target uint32, internalformat uint32, width int32, height int32) {
+	gl.RenderbufferStorage(target, internalformat, width, height)
+}
 func (_ GLImpl) ReadPixels(x int32, y int32, width int32, height int32, format uint32, xtype uint32, pixels unsafe.Pointer) {
 	gl.ReadPixels(x, y, width, height, format, xtype, pixels)
 }

openglinterface.go

@@ -797,9 +797,12 @@ type GL interface {
 	ActiveTexture(texture uint32)
 	AttachShader(program uint32, shader uint32)
 	BindBuffer(target uint32, buffer uint32)
+	BindFramebuffer(target uint32, framebuffer uint32)
+	BindRenderbuffer(target uint32, renderbuffer uint32)
 	BindTexture(target uint32, texture uint32)
 	BlendFunc(sfactor uint32, dfactor uint32)
 	BufferData(target uint32, size int, data unsafe.Pointer, usage uint32)
+	CheckFramebufferStatus(target uint32) uint32
 	Clear(mask uint32)
 	ClearColor(red float32, green float32, blue float32, alpha float32)
 	ColorMask(red bool, green bool, blue bool, alpha bool)
@@ -807,13 +810,19 @@ type GL interface {
 	CreateProgram() uint32
 	CreateShader(xtype uint32) uint32
 	DeleteShader(shader uint32)
+	DeleteFramebuffers(n int32, framebuffers *uint32)
+	DeleteRenderbuffers(n int32, renderbuffers *uint32)
 	DeleteTextures(n int32, textures *uint32)
 	Disable(cap uint32)
 	DisableVertexAttribArray(index uint32)
 	DrawArrays(mode uint32, first int32, count int32)
 	Enable(cap uint32)
 	EnableVertexAttribArray(index uint32)
+	FramebufferRenderbuffer(target uint32, attachment uint32, renderbuffertarget uint32, renderbuffer uint32)
+	FramebufferTexture(target uint32, attachment uint32, texture uint32, level int32)
 	GenBuffers(n int32, buffers *uint32)
+	GenFramebuffers(n int32, framebuffers *uint32)
+	GenRenderbuffers(n int32, renderbuffers *uint32)
 	GenTextures(n int32, textures *uint32)
 	GenerateMipmap(target uint32)
 	GetAttribLocation(program uint32, name string) int32
@@ -825,6 +834,7 @@ type GL interface {
 	GetUniformLocation(program uint32, name string) int32
 	LinkProgram(program uint32)
 	ReadPixels(x int32, y int32, width int32, height int32, format uint32, xtype uint32, pixels unsafe.Pointer)
+	RenderbufferStorage(target uint32, internalformat uint32, width int32, height int32)
 	Scissor(x int32, y int32, width int32, height int32)
 	ShaderSource(shader uint32, source string)
 	StencilFunc(xfunc uint32, ref int32, mask uint32)