gpu,gpu/gl: specialize Buffer.Bind to Buffer.BindIndex

Direct3D can't support a generic Bind, and we don't need it now
BindVertex was added.

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

gpu/backend.go

@@ -116,7 +116,7 @@ type Uniform interface{}
 
 type Buffer interface {
 	BindVertex(stride, offset int)
-	Bind()
+	BindIndex()
 	Release()
 }
 

gpu/gl/backend.go

@@ -174,7 +174,7 @@ func (b *Backend) NewBuffer(typ gpu.BufferType, data []byte) gpu.Buffer {
 		panic("unsupported buffer type")
 	}
 	buf := &gpuBuffer{backend: b, obj: obj, typ: gltyp}
-	buf.Bind()
+	b.funcs.BindBuffer(gltyp, obj)
 	b.funcs.BufferData(gltyp, data, STATIC_DRAW)
 	return buf
 }
@@ -395,8 +395,11 @@ func (b *Backend) setupVertexArrays() {
 	}
 }
 
-func (b *gpuBuffer) Bind() {
+func (b *gpuBuffer) BindIndex() {
-	b.backend.funcs.BindBuffer(b.typ, b.obj)
+	if b.typ != ELEMENT_ARRAY_BUFFER {
+		panic("not an index buffer")
+	}
+	b.backend.funcs.BindBuffer(ELEMENT_ARRAY_BUFFER, b.obj)
 }
 
 func (f *gpuFramebuffer) IsComplete() error {

gpu/path.go

@@ -294,7 +294,7 @@ func (s *stenciler) begin(sizes []image.Point) {
 	s.ctx.ClearColor(0.0, 0.0, 0.0, 0.0)
 	s.prog.Bind()
 	s.progLayout.Bind()
-	s.indexBuf.Bind()
+	s.indexBuf.BindIndex()
 }
 
 func (s *stenciler) stencilPath(bounds image.Rectangle, offset f32.Point, uv image.Point, data *pathData) {