gpu,gpu/gl: introduce InputLayout and use shader reflection data

InputLayout is the abstraction for the mapping between vertex data and
shader inputs. The mapping is implicit in OpenGL but explicit in
Direct3D.

Infer the attribute name location index using shader reflection data,
and get rid of a parameter to NewProgram.

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

gpu/backend.go

@@ -23,8 +23,8 @@ type Backend interface {
 	NilTexture() Texture
 	NewFramebuffer() Framebuffer
 	NewBuffer(typ BufferType, data []byte) Buffer
-	NewProgram(vertexShader, fragmentShader ShaderSources, attribMap []string) (Program, error)
-	SetupVertexArray(slot int, size int, dataType DataType, stride, offset int)
+	NewProgram(vertexShader, fragmentShader ShaderSources) (Program, error)
+	NewInputLayout(vertexShader ShaderSources, layout []InputDesc) (InputLayout, error)
 
 	DepthFunc(f DepthFunc)
 	ClearColor(r, g, b, a float32)
@@ -65,6 +65,21 @@ type InputLocation struct {
 	Size int
 }
 
+// InputDesc describes a vertex attribute as laid out in a Buffer.
+type InputDesc struct {
+	Type DataType
+	Size int
+
+	Offset int
+}
+
+// InputLayout is the backend specific representation of the mapping
+// between Buffers and shader attributes.
+type InputLayout interface {
+	Bind()
+	Release()
+}
+
 type BlendFactor uint8
 
 type DrawMode uint8
@@ -100,6 +115,7 @@ type Program interface {
 type Uniform interface{}
 
 type Buffer interface {
+	BindVertex(stride, offset int)
 	Bind()
 	Release()
 }