gpu: add depthBits parameter to NewFramebuffer

Along with ReadPixels in the next change, a Framebuffer with depth is enough to
implement screenshot functionality on top of any Backend.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

gpu/backend.go

@@ -20,7 +20,7 @@ type Backend interface {
 	IsTimeContinuous() bool
 	NewTexture(format TextureFormat, width, height int, minFilter, magFilter TextureFilter, bindings BufferBinding) (Texture, error)
 	DefaultFramebuffer() Framebuffer
-	NewFramebuffer(tex Texture) (Framebuffer, error)
+	NewFramebuffer(tex Texture, depthBits int) (Framebuffer, error)
 	NewImmutableBuffer(typ BufferBinding, data []byte) (Buffer, error)
 	NewBuffer(typ BufferBinding, size int) (Buffer, error)
 	NewProgram(vertexShader, fragmentShader ShaderSources) (Program, error)

gpu/gl/backend.go

@@ -54,11 +54,15 @@ type gpuTexture struct {
 	backend *Backend
 	obj     Texture
 	triple  textureTriple
+	width   int
+	height  int
 }
 
 type gpuFramebuffer struct {
-	funcs Functions
+	funcs    Functions
-	obj   Framebuffer
+	obj      Framebuffer
+	hasDepth bool
+	depthBuf Renderbuffer
 }
 
 type gpuBuffer struct {
@@ -162,7 +166,7 @@ func (b *Backend) IsTimeContinuous() bool {
 	return b.funcs.GetInteger(GPU_DISJOINT_EXT) == FALSE
 }
 
-func (b *Backend) NewFramebuffer(tex gpu.Texture) (gpu.Framebuffer, error) {
+func (b *Backend) NewFramebuffer(tex gpu.Texture, depthBits int) (gpu.Framebuffer, error) {
 	glErr(b.funcs)
 	gltex := tex.(*gpuTexture)
 	fb := b.funcs.CreateFramebuffer()
@@ -173,6 +177,24 @@ func (b *Backend) NewFramebuffer(tex gpu.Texture) (gpu.Framebuffer, error) {
 		return nil, err
 	}
 	b.funcs.FramebufferTexture2D(FRAMEBUFFER, COLOR_ATTACHMENT0, TEXTURE_2D, gltex.obj, 0)
+	if depthBits > 0 {
+		size := Enum(DEPTH_COMPONENT16)
+		switch {
+		case depthBits > 24:
+			size = DEPTH_COMPONENT32F
+		case depthBits > 16:
+			size = DEPTH_COMPONENT24
+		}
+		depthBuf := b.funcs.CreateRenderbuffer()
+		b.funcs.BindRenderbuffer(RENDERBUFFER, depthBuf)
+		b.funcs.RenderbufferStorage(RENDERBUFFER, size, gltex.width, gltex.height)
+		fbo.depthBuf = depthBuf
+		fbo.hasDepth = true
+		if err := glErr(b.funcs); err != nil {
+			fbo.Release()
+			return nil, err
+		}
+	}
 	if st := b.funcs.CheckFramebufferStatus(FRAMEBUFFER); st != FRAMEBUFFER_COMPLETE {
 		fbo.Release()
 		return nil, fmt.Errorf("incomplete framebuffer, status = 0x%x, err = %d", st, b.funcs.GetError())
@@ -186,7 +208,7 @@ func (b *Backend) DefaultFramebuffer() gpu.Framebuffer {
 
 func (b *Backend) NewTexture(format gpu.TextureFormat, width, height int, minFilter, magFilter gpu.TextureFilter, binding gpu.BufferBinding) (gpu.Texture, error) {
 	glErr(b.funcs)
-	tex := &gpuTexture{backend: b, obj: b.funcs.CreateTexture()}
+	tex := &gpuTexture{backend: b, obj: b.funcs.CreateTexture(), width: width, height: height}
 	switch format {
 	case gpu.TextureFormatFloat:
 		tex.triple = b.floatTriple
@@ -578,6 +600,9 @@ func (f *gpuFramebuffer) Invalidate() {
 
 func (f *gpuFramebuffer) Release() {
 	f.funcs.DeleteFramebuffer(f.obj)
+	if f.hasDepth {
+		f.funcs.DeleteRenderbuffer(f.depthBuf)
+	}
 }
 
 func toTexFilter(f gpu.TextureFilter) int {

gpu/gl/gl.go

@@ -17,6 +17,8 @@ const (
 	DEPTH_BUFFER_BIT                      = 0x100
 	DEPTH_ATTACHMENT                      = 0x8d00
 	DEPTH_COMPONENT16                     = 0x81a5
+	DEPTH_COMPONENT24                     = 0x81A6
+	DEPTH_COMPONENT32F                    = 0x8CAC
 	DEPTH_TEST                            = 0xb71
 	DST_COLOR                             = 0x306
 	ELEMENT_ARRAY_BUFFER                  = 0x8893
@@ -91,6 +93,7 @@ type Functions interface {
 	BindAttribLocation(p Program, a Attrib, name string)
 	BindBuffer(target Enum, b Buffer)
 	BindFramebuffer(target Enum, fb Framebuffer)
+	BindRenderbuffer(target Enum, fb Renderbuffer)
 	BindTexture(target Enum, t Texture)
 	BlendEquation(mode Enum)
 	BlendFunc(sfactor, dfactor Enum)
@@ -104,12 +107,14 @@ type Functions interface {
 	CreateFramebuffer() Framebuffer
 	CreateProgram() Program
 	CreateQuery() Query
+	CreateRenderbuffer() Renderbuffer
 	CreateShader(ty Enum) Shader
 	CreateTexture() Texture
 	DeleteBuffer(v Buffer)
 	DeleteFramebuffer(v Framebuffer)
 	DeleteProgram(p Program)
 	DeleteQuery(query Query)
+	DeleteRenderbuffer(r Renderbuffer)
 	DeleteShader(s Shader)
 	DeleteTexture(v Texture)
 	DepthFunc(f Enum)
@@ -134,6 +139,7 @@ type Functions interface {
 	GetUniformLocation(p Program, name string) Uniform
 	InvalidateFramebuffer(target, attachment Enum)
 	LinkProgram(p Program)
+	RenderbufferStorage(target, internalformat Enum, width, height int)
 	ShaderSource(s Shader, src string)
 	TexImage2D(target Enum, level int, internalFormat int, width, height int, format, ty Enum, data []byte)
 	TexParameteri(target, pname Enum, param int)

gpu/path.go

@@ -213,7 +213,7 @@ func (s *fboSet) resize(ctx Backend, sizes []image.Point) {
 			}
 			tex, err := ctx.NewTexture(TextureFormatFloat, sz.X, sz.Y, FilterNearest, FilterNearest,
 				BufferBindingTexture|BufferBindingFramebuffer)
-			fbo, err := ctx.NewFramebuffer(tex)
+			fbo, err := ctx.NewFramebuffer(tex, 0)
 			if err != nil {
 				panic(err)
 			}