render

type Context interface {
	Init() (err error)               // Call first, once at startup.
	Clear()                          // Clear all buffers before rendering.
	Color(r, g, b, a float32)        // Set the default render clear color
	Enable(attr uint32, enable bool) // Enable or disable graphic state.
	Viewport(width int, height int)  // Set the available screen real estate.

	// Rendering works with uniform values and data bound to the GPU.
	BindMesh(vao *uint32, vdata map[uint32]Data, fdata Data) error
	BindShader(vsh, fsh []string, uniforms map[string]int32,
		layouts map[string]uint32) (program uint32, err error)
	BindTexture(tid *uint32, img image.Image) error
	SetTextureMode(tid uint32, clamp bool)
	Render(d *Draw) // Render bound data, textures with bound shaders.

	// BindMap creates a framebuffer object with an associated
	// texture that can be used for shadow maps.
	//   fbo : returned frame buffer object identifier.
	//   tid : returned texture identifier.
	BindMap(fbo, tid *uint32) error

	// BindTarget creates a framebuffer object that can be used
	// as a render target.
	//   fbo : returned frame buffer object identifier.
	//   tid : returned texture identifier.
	//   db  : returned depth buffer render buffer.
	BindTarget(fbo, tid, db *uint32) error

	// Releasing frees up previous bound graphics card data.
	ReleaseMesh(vao uint32)            // Free bound vao reference.
	ReleaseShader(sid uint32)          // Free bound shader reference.
	ReleaseTexture(tid uint32)         // Free bound texture reference.
	ReleaseMap(fbo, tid uint32)        // Free shadow map framebuffer.
	ReleaseTarget(fbo, tid, db uint32) // Free render target framebuffer.
}

type Data interface {
	Set(data interface{}) // Copy data in. Invalid types are logged.
	Len() int             // Number of elements.
	Size() uint32         // Number of bytes
	Clone() Data          // Duplicate.
}

type Draw struct {
	Shader uint32 // Bind reference for all shader programs.
	Vao    uint32 // Bind reference for all vertex buffers.
	Mode   int    // Points, Lines, Triangles
	Texs   []tex  // GPU bound texture references.
	Shtex  uint32 // GPU bound texture shadow depth map.
	Tag    uint32 // Application tag for debugging. Commonly an Entity id.

	// Rendering hints.
	Bucket    uint64 // Used to sort draws. Lower buckets rendered first.
	Depth     bool   // True to render with depth.
	Scissor   bool   // True to render with within scissor dimensions.
	Sx, Sy    int32  // Start of scissor area. First 2 parameters.
	Sw, Sh    int32  // Scissor width and height. Last 2 parameters.
	Fbo       uint32 // Framebuffer id. 0 for default.
	FaceCnt   int32  // Number of triangles to be rendered.
	VertCnt   int32  // Number of verticies to be rendered.
	Instances int32  // Postive instance count for instanced mesh.

	// Shader uniform data. The Uniforms are queried from the shader.
	// The UniformData is set by the Engine and App.
	Uniforms    map[string]int32    // Shader uniform variables, references.
	UniformData map[int32][]float32 // Uniform values indexed by ref.

	// Animation pose matrices are converted to a single slice.
	NumPoses int       // Number of animation bone data matricies.
	Poses    []float32 // All the bone data matricies.
}