gpu: introduce pipeline abstraction

Modern API such as Metal and Vulkan want clients to compile expensive
state changes into pipeline objects. Change our GPU driver abstraction
to match, thereby paving the way for future drivers.

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

gpu/internal/driver/driver.go

@@ -26,23 +26,25 @@ type Device interface {
 	NewImmutableBuffer(typ BufferBinding, data []byte) (Buffer, error)
 	NewBuffer(typ BufferBinding, size int) (Buffer, error)
 	NewComputeProgram(shader shader.Sources) (Program, error)
-	NewProgram(vertexShader, fragmentShader shader.Sources) (Program, error)
-	NewInputLayout(vertexShader shader.Sources, layout []shader.InputDesc) (InputLayout, error)
+	NewVertexShader(src shader.Sources) (VertexShader, error)
+	NewFragmentShader(src shader.Sources) (FragmentShader, error)
+	NewPipeline(desc PipelineDesc) (Pipeline, error)
 
 	Clear(r, g, b, a float32)
 	Viewport(x, y, width, height int)
 	DrawArrays(mode DrawMode, off, count int)
 	DrawElements(mode DrawMode, off, count int)
-	SetBlend(enable bool)
-	BlendFunc(sfactor, dfactor BlendFactor)
 
-	BindInputLayout(i InputLayout)
 	BindProgram(p Program)
+	BindPipeline(p Pipeline)
 	BindFramebuffer(f Framebuffer)
 	BindTexture(unit int, t Texture)
 	BindVertexBuffer(b Buffer, stride, offset int)
 	BindIndexBuffer(b Buffer)
 	BindImageTexture(unit int, texture Texture, access AccessBits, format TextureFormat)
+	BindVertexUniforms(buf Buffer)
+	BindFragmentUniforms(buf Buffer)
+	BindStorageBuffer(binding int, buf Buffer)
 
 	BlitFramebuffer(dst, src Framebuffer, srect, drect image.Rectangle)
 	MemoryBarrier()
@@ -51,12 +53,23 @@ type Device interface {
 	Release()
 }
 
-// InputLayout is the driver specific representation of the mapping
-// between Buffers and shader attributes.
-type InputLayout interface {
+type Pipeline interface {
 	Release()
 }
 
+type PipelineDesc struct {
+	VertexShader   VertexShader
+	FragmentShader FragmentShader
+	VertexLayout   []shader.InputDesc
+	BlendDesc      BlendDesc
+	PixelFormat    TextureFormat
+}
+
+type BlendDesc struct {
+	Enable               bool
+	SrcFactor, DstFactor BlendFactor
+}
+
 type AccessBits uint8
 
 type BlendFactor uint8
@@ -78,11 +91,16 @@ type Caps struct {
 	MaxTextureSize   int
 }
 
+type VertexShader interface {
+	Release()
+}
+
+type FragmentShader interface {
+	Release()
+}
+
 type Program interface {
 	Release()
-	SetStorageBuffer(binding int, buf Buffer)
-	SetVertexUniforms(buf Buffer)
-	SetFragmentUniforms(buf Buffer)
 }
 
 type Buffer interface {
@@ -123,6 +141,8 @@ const (
 	TextureFormatSRGBA TextureFormat = iota
 	TextureFormatFloat
 	TextureFormatRGBA8
+	// TextureFormatOutput denotes the format used by the output framebuffer.
+	TextureFormatOutput
 )
 
 const (