gpu/internal/shaders: generate shader variants

We're about to add Direct3D support, where shaders are written in
HLSL. Rather than write shaders twice (or more), convert them to
a GLSL variant understood by the glslcc cross-compiler and generate
the OpenGL ES 2.0 and HLSL variants. The HLSL is used by a future
change.

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

gpu/backend.go

@@ -23,7 +23,7 @@ type Backend interface {
 	NilTexture() Texture
 	NewFramebuffer() Framebuffer
 	NewBuffer(typ BufferType, data []byte) Buffer
-	NewProgram(vertexShader, fragmentShader string, attribMap []string) (Program, error)
+	NewProgram(vertexShader, fragmentShader ShaderSources, attribMap []string) (Program, error)
 	SetupVertexArray(slot int, size int, dataType DataType, stride, offset int)
 
 	DepthFunc(f DepthFunc)
@@ -39,6 +39,32 @@ type Backend interface {
 	BlendFunc(sfactor, dfactor BlendFactor)
 }
 
+type ShaderSources struct {
+	GLES2    string
+	HLSL     []byte
+	Uniforms []UniformLocation
+	Inputs   []InputLocation
+}
+
+type UniformLocation struct {
+	Name   string
+	Type   DataType
+	Size   int
+	Offset int
+}
+
+type InputLocation struct {
+	// For GLSL.
+	Name     string
+	Location int
+	// For HLSL.
+	Semantic      string
+	SemanticIndex int
+
+	Type DataType
+	Size int
+}
+
 type BlendFactor uint8
 
 type DrawMode uint8