gpu: make Buffers immutable

The GPU implementation only uses immutable buffers so far, so let's
make it easy and performant for the backends.

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

gpu/backend.go

@@ -22,7 +22,7 @@ type Backend interface {
 	DefaultFramebuffer() Framebuffer
 	NilTexture() Texture
 	NewFramebuffer() Framebuffer
-	NewBuffer(typ BufferType) Buffer
+	NewBuffer(typ BufferType, data []byte) Buffer
 	NewProgram(vertexShader, fragmentShader string, attribMap []string) (Program, error)
 	SetupVertexArray(slot int, size int, dataType DataType, stride, offset int)
 
@@ -49,7 +49,6 @@ type TextureFilter uint8
 type TextureFormat uint8
 
 type BufferType uint8
-type BufferUsage uint8
 
 type DataType uint8
 
@@ -76,7 +75,6 @@ type Uniform interface{}
 
 type Buffer interface {
 	Bind()
-	Upload(usage BufferUsage, data []byte)
 	Release()
 }
 
@@ -116,10 +114,6 @@ const (
 	DataTypeShort
 )
 
-const (
-	BufferUsageStaticDraw BufferUsage = iota
-)
-
 const (
 	BufferTypeIndices BufferType = iota
 	BufferTypeData

gpu/gl/backend.go

@@ -148,7 +148,7 @@ func (b *Backend) NewTexture(minFilter, magFilter gpu.TextureFilter) gpu.Texture
 	return tex
 }
 
-func (b *Backend) NewBuffer(typ gpu.BufferType) gpu.Buffer {
+func (b *Backend) NewBuffer(typ gpu.BufferType, data []byte) gpu.Buffer {
 	obj := b.funcs.CreateBuffer()
 	var gltyp Enum
 	switch typ {
@@ -159,7 +159,10 @@ func (b *Backend) NewBuffer(typ gpu.BufferType) gpu.Buffer {
 	default:
 		panic("unsupported buffer type")
 	}
-	return &gpuBuffer{funcs: b.funcs, obj: obj, typ: gltyp}
+	buf := &gpuBuffer{funcs: b.funcs, obj: obj, typ: gltyp}
+	buf.Bind()
+	b.funcs.BufferData(gltyp, data, STATIC_DRAW)
+	return buf
 }
 
 func (b *Backend) bindTexture(unit int, t *gpuTexture) {
@@ -344,18 +347,6 @@ func (b *gpuBuffer) Bind() {
 	b.funcs.BindBuffer(b.typ, b.obj)
 }
 
-func (b *gpuBuffer) Upload(usage gpu.BufferUsage, data []byte) {
-	b.Bind()
-	var glusage Enum
-	switch usage {
-	case gpu.BufferUsageStaticDraw:
-		glusage = STATIC_DRAW
-	default:
-		panic("unsupported buffer usage")
-	}
-	b.funcs.BufferData(b.typ, data, glusage)
-}
-
 func (f *gpuFramebuffer) IsComplete() error {
 	if st := f.funcs.CheckFramebufferStatus(FRAMEBUFFER); st != FRAMEBUFFER_COMPLETE {
 		return fmt.Errorf("incomplete framebuffer, status = 0x%x, err = %d", st, f.funcs.GetError())

gpu/gpu.go

@@ -380,14 +380,14 @@ func newBlitter(ctx Backend) *blitter {
 	if err != nil {
 		panic(err)
 	}
-	quadVerts := ctx.NewBuffer(BufferTypeData)
-	quadVerts.Upload(BufferUsageStaticDraw,
+	quadVerts := ctx.NewBuffer(BufferTypeData,
 		gunsafe.BytesView([]float32{
 			-1, +1, 0, 0,
 			+1, +1, 1, 0,
 			-1, -1, 0, 1,
 			+1, -1, 1, 1,
-		}))
+		}),
+	)
 	b := &blitter{
 		ctx:       ctx,
 		prog:      prog,

gpu/path.go

@@ -143,8 +143,7 @@ func newStenciler(ctx Backend) *stenciler {
 		indices[i*6+4] = i*4 + 1
 		indices[i*6+5] = i*4 + 3
 	}
-	indexBuf := ctx.NewBuffer(BufferTypeIndices)
-	indexBuf.Upload(BufferUsageStaticDraw, gunsafe.BytesView(indices))
+	indexBuf := ctx.NewBuffer(BufferTypeIndices, gunsafe.BytesView(indices))
 	return &stenciler{
 		ctx:                ctx,
 		defFBO:             defFBO,
@@ -218,8 +217,7 @@ func (c *coverer) release() {
 }
 
 func buildPath(ctx Backend, p []byte) *pathData {
-	buf := ctx.NewBuffer(BufferTypeData)
-	buf.Upload(BufferUsageStaticDraw, p)
+	buf := ctx.NewBuffer(BufferTypeData, p)
 	return &pathData{
 		ncurves: len(p) / path.VertStride,
 		data:    buf,