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()
 }

gpu/gl/backend.go

@@ -34,6 +34,14 @@ type glstate struct {
 	nattr    int
 	prog     *gpuProgram
 	texUnits [2]*gpuTexture
+	layout   *gpuInputLayout
+	buffer   bufferBinding
+}
+
+type bufferBinding struct {
+	buf    *gpuBuffer
+	offset int
+	stride int
 }
 
 type gpuTimer struct {
@@ -52,9 +60,9 @@ type gpuFramebuffer struct {
 }
 
 type gpuBuffer struct {
-	funcs Functions
-	obj   Buffer
-	typ   Enum
+	backend *Backend
+	obj     Buffer
+	typ     Enum
 }
 
 type gpuProgram struct {
@@ -63,6 +71,12 @@ type gpuProgram struct {
 	nattr   int
 }
 
+type gpuInputLayout struct {
+	backend *Backend
+	inputs  []gpu.InputLocation
+	layout  []gpu.InputDesc
+}
+
 // textureTriple holds the type settings for
 // a TexImage2D call.
 type textureTriple struct {
@@ -159,7 +173,7 @@ func (b *Backend) NewBuffer(typ gpu.BufferType, data []byte) gpu.Buffer {
 	default:
 		panic("unsupported buffer type")
 	}
-	buf := &gpuBuffer{funcs: b.funcs, obj: obj, typ: gltyp}
+	buf := &gpuBuffer{backend: b, obj: obj, typ: gltyp}
 	buf.Bind()
 	b.funcs.BufferData(gltyp, data, STATIC_DRAW)
 	return buf
@@ -232,10 +246,12 @@ func (b *Backend) SetBlend(enable bool) {
 }
 
 func (b *Backend) DrawElements(mode gpu.DrawMode, off, count int) {
+	b.setupVertexArrays()
 	b.funcs.DrawElements(toGLDrawMode(mode), count, UNSIGNED_SHORT, off)
 }
 
 func (b *Backend) DrawArrays(mode gpu.DrawMode, off, count int) {
+	b.setupVertexArrays()
 	b.funcs.DrawArrays(toGLDrawMode(mode), off, count)
 }
 
@@ -284,7 +300,27 @@ func (b *Backend) DepthFunc(f gpu.DepthFunc) {
 	b.funcs.DepthFunc(glfunc)
 }
 
-func (b *Backend) NewProgram(vssrc, fssrc gpu.ShaderSources, attr []string) (gpu.Program, error) {
+func (b *Backend) NewInputLayout(vs gpu.ShaderSources, layout []gpu.InputDesc) (gpu.InputLayout, error) {
+	if len(vs.Inputs) != len(layout) {
+		return nil, fmt.Errorf("NewInputLayout: got %d inputs, expected %d", len(layout), len(vs.Inputs))
+	}
+	for i, inp := range vs.Inputs {
+		if exp, got := inp.Size, layout[i].Size; exp != got {
+			return nil, fmt.Errorf("NewInputLayout: data size mismatch for %q: got %d expected %d", inp.Name, got, exp)
+		}
+	}
+	return &gpuInputLayout{
+		backend: b,
+		inputs:  vs.Inputs,
+		layout:  layout,
+	}, nil
+}
+
+func (b *Backend) NewProgram(vssrc, fssrc gpu.ShaderSources) (gpu.Program, error) {
+	attr := make([]string, len(vssrc.Inputs))
+	for _, inp := range vssrc.Inputs {
+		attr[inp.Location] = inp.Name
+	}
 	p, err := CreateProgram(b.funcs, vssrc.GLES2, fssrc.GLES2, attr)
 	if err != nil {
 		return nil, err
@@ -322,29 +358,45 @@ func (p *gpuProgram) UniformFor(uniform string) gpu.Uniform {
 	return GetUniformLocation(f, p.obj, uniform)
 }
 
-func (b *Backend) SetupVertexArray(slot int, size int, dataType gpu.DataType, stride, offset int) {
-	var gltyp Enum
-	switch dataType {
-	case gpu.DataTypeFloat:
-		gltyp = FLOAT
-	case gpu.DataTypeShort:
-		gltyp = SHORT
-	default:
-		panic("unsupported data type")
-	}
-	b.funcs.VertexAttribPointer(Attrib(slot), size, gltyp, false, stride, offset)
-}
-
 func (p *gpuProgram) Release() {
 	p.backend.funcs.DeleteProgram(p.obj)
 }
 
 func (b *gpuBuffer) Release() {
-	b.funcs.DeleteBuffer(b.obj)
+	b.backend.funcs.DeleteBuffer(b.obj)
+}
+
+func (b *gpuBuffer) BindVertex(stride, offset int) {
+	if b.typ != ARRAY_BUFFER {
+		panic("not a vertex buffer")
+	}
+	b.backend.state.buffer = bufferBinding{buf: b, stride: stride, offset: offset}
+}
+
+func (b *Backend) setupVertexArrays() {
+	layout := b.state.layout
+	if layout == nil {
+		panic("no input layout is current")
+	}
+	buf := b.state.buffer
+	b.funcs.BindBuffer(ARRAY_BUFFER, buf.buf.obj)
+	for i, inp := range layout.inputs {
+		l := layout.layout[i]
+		var gltyp Enum
+		switch l.Type {
+		case gpu.DataTypeFloat:
+			gltyp = FLOAT
+		case gpu.DataTypeShort:
+			gltyp = SHORT
+		default:
+			panic("unsupported data type")
+		}
+		b.funcs.VertexAttribPointer(Attrib(inp.Location), l.Size, gltyp, false, buf.stride, buf.offset+l.Offset)
+	}
 }
 
 func (b *gpuBuffer) Bind() {
-	b.funcs.BindBuffer(b.typ, b.obj)
+	b.backend.funcs.BindBuffer(b.typ, b.obj)
 }
 
 func (f *gpuFramebuffer) IsComplete() error {
@@ -437,6 +489,12 @@ func (t *gpuTimer) Duration() (time.Duration, bool) {
 	return time.Duration(nanos), true
 }
 
+func (l *gpuInputLayout) Bind() {
+	l.backend.state.layout = l
+}
+
+func (l *gpuInputLayout) Release() {}
+
 // floatTripleFor determines the best texture triple for floating point FBOs.
 func floatTripleFor(f Functions, ver [2]int, exts []string) (textureTriple, error) {
 	var triples []textureTriple

gpu/gpu.go

@@ -212,6 +212,7 @@ type blitter struct {
 	ctx      Backend
 	viewport image.Point
 	prog     [2]Program
+	layout   InputLayout
 	vars     [2]struct {
 		z                   Uniform
 		uScale, uOffset     Uniform
@@ -234,10 +235,6 @@ const (
 	materialTexture
 )
 
-var (
-	blitAttribs = []string{"pos", "uv"}
-)
-
 const (
 	attribPos = 0
 	attribUV  = 1
@@ -375,7 +372,7 @@ func (r *renderer) release() {
 }
 
 func newBlitter(ctx Backend) *blitter {
-	prog, err := createColorPrograms(ctx, shader_blit_vert, shader_blit_frag)
+	prog, layout, err := createColorPrograms(ctx, shader_blit_vert, shader_blit_frag)
 	if err != nil {
 		panic(err)
 	}
@@ -390,6 +387,7 @@ func newBlitter(ctx Backend) *blitter {
 	b := &blitter{
 		ctx:       ctx,
 		prog:      prog,
+		layout:    layout,
 		quadVerts: quadVerts,
 	}
 	for i, prog := range prog {
@@ -414,21 +412,31 @@ func (b *blitter) release() {
 	for _, p := range b.prog {
 		p.Release()
 	}
+	b.layout.Release()
 }
 
-func createColorPrograms(ctx Backend, vsSrc ShaderSources, fsSrc [2]ShaderSources) ([2]Program, error) {
+func createColorPrograms(ctx Backend, vsSrc ShaderSources, fsSrc [2]ShaderSources) ([2]Program, InputLayout, error) {
 	var prog [2]Program
 	var err error
-	prog[materialTexture], err = ctx.NewProgram(vsSrc, fsSrc[materialTexture], blitAttribs)
+	prog[materialTexture], err = ctx.NewProgram(vsSrc, fsSrc[materialTexture])
 	if err != nil {
-		return prog, err
+		return prog, nil, err
 	}
-	prog[materialColor], err = ctx.NewProgram(vsSrc, fsSrc[materialColor], blitAttribs)
+	prog[materialColor], err = ctx.NewProgram(vsSrc, fsSrc[materialColor])
 	if err != nil {
 		prog[materialTexture].Release()
-		return prog, err
+		return prog, nil, err
 	}
-	return prog, nil
+	layout, err := ctx.NewInputLayout(vsSrc, []InputDesc{
+		{Type: DataTypeFloat, Size: 2, Offset: 0},
+		{Type: DataTypeFloat, Size: 2, Offset: 4 * 2},
+	})
+	if err != nil {
+		prog[materialTexture].Release()
+		prog[materialColor].Release()
+		return prog, nil, err
+	}
+	return prog, layout, nil
 }
 
 func (r *renderer) stencilClips(pathCache *opCache, ops []*pathOp) {
@@ -456,9 +464,8 @@ func (r *renderer) intersect(ops []imageOp) {
 	}
 	fbo := -1
 	r.pather.stenciler.beginIntersect(r.intersections.sizes)
-	r.blitter.quadVerts.Bind()
-	r.ctx.SetupVertexArray(attribPos, 2, DataTypeFloat, 4*4, 0)
-	r.ctx.SetupVertexArray(attribUV, 2, DataTypeFloat, 4*4, 4*2)
+	r.blitter.quadVerts.BindVertex(4*4, 0)
+	r.pather.stenciler.iprogLayout.Bind()
 	for _, img := range ops {
 		if img.clipType != clipTypeIntersection {
 			continue
@@ -764,9 +771,8 @@ func (d *drawState) materialFor(cache *resourceCache, rect f32.Rectangle, off f3
 
 func (r *renderer) drawZOps(ops []imageOp) {
 	r.ctx.SetDepthTest(true)
-	r.blitter.quadVerts.Bind()
-	r.ctx.SetupVertexArray(attribPos, 2, DataTypeFloat, 4*4, 0)
-	r.ctx.SetupVertexArray(attribUV, 2, DataTypeFloat, 4*4, 4*2)
+	r.blitter.quadVerts.BindVertex(4*4, 0)
+	r.blitter.layout.Bind()
 	// Render front to back.
 	for i := len(ops) - 1; i >= 0; i-- {
 		img := ops[i]
@@ -786,9 +792,8 @@ func (r *renderer) drawOps(ops []imageOp) {
 	r.ctx.SetDepthTest(true)
 	r.ctx.DepthMask(false)
 	r.ctx.BlendFunc(BlendFactorOne, BlendFactorOneMinusSrcAlpha)
-	r.blitter.quadVerts.Bind()
-	r.ctx.SetupVertexArray(attribPos, 2, DataTypeFloat, 4*4, 0)
-	r.ctx.SetupVertexArray(attribUV, 2, DataTypeFloat, 4*4, 4*2)
+	r.blitter.quadVerts.BindVertex(4*4, 0)
+	r.pather.coverer.layout.Bind()
 	var coverTex Texture
 	for _, img := range ops {
 		m := img.material

gpu/path.go

@@ -24,9 +24,10 @@ type pather struct {
 }
 
 type coverer struct {
-	ctx  Backend
-	prog [2]Program
-	vars [2]struct {
+	ctx    Backend
+	prog   [2]Program
+	layout InputLayout
+	vars   [2]struct {
 		z                             Uniform
 		uScale, uOffset               Uniform
 		uUVScale, uUVOffset           Uniform
@@ -39,7 +40,9 @@ type stenciler struct {
 	ctx                Backend
 	defFBO             Framebuffer
 	prog               Program
+	progLayout         InputLayout
 	iprog              Program
+	iprogLayout        InputLayout
 	fbos               fboSet
 	intersections      fboSet
 	uScale, uOffset    Uniform
@@ -64,11 +67,6 @@ type pathData struct {
 	data    Buffer
 }
 
-var (
-	pathAttribs      = []string{"corner", "maxy", "from", "ctrl", "to"}
-	intersectAttribs = []string{"pos", "uv"}
-)
-
 const (
 	// Number of path quads per draw batch.
 	pathBatchSize = 10000
@@ -91,13 +89,14 @@ func newPather(ctx Backend) *pather {
 }
 
 func newCoverer(ctx Backend) *coverer {
-	prog, err := createColorPrograms(ctx, shader_cover_vert, shader_cover_frag)
+	prog, layout, err := createColorPrograms(ctx, shader_cover_vert, shader_cover_frag)
 	if err != nil {
 		panic(err)
 	}
 	c := &coverer{
-		ctx:  ctx,
-		prog: prog,
+		ctx:    ctx,
+		prog:   prog,
+		layout: layout,
 	}
 	for i, prog := range prog {
 		switch materialType(i) {
@@ -122,11 +121,11 @@ func newCoverer(ctx Backend) *coverer {
 
 func newStenciler(ctx Backend) *stenciler {
 	defFBO := ctx.DefaultFramebuffer()
-	prog, err := ctx.NewProgram(shader_stencil_vert, shader_stencil_frag, pathAttribs)
+	prog, err := ctx.NewProgram(shader_stencil_vert, shader_stencil_frag)
 	if err != nil {
 		panic(err)
 	}
-	iprog, err := ctx.NewProgram(shader_intersect_vert, shader_intersect_frag, intersectAttribs)
+	iprog, err := ctx.NewProgram(shader_intersect_vert, shader_intersect_frag)
 	if err != nil {
 		panic(err)
 	}
@@ -144,11 +143,30 @@ func newStenciler(ctx Backend) *stenciler {
 		indices[i*6+5] = i*4 + 3
 	}
 	indexBuf := ctx.NewBuffer(BufferTypeIndices, gunsafe.BytesView(indices))
+	progLayout, err := ctx.NewInputLayout(shader_stencil_vert, []InputDesc{
+		{Type: DataTypeShort, Size: 2, Offset: int(unsafe.Offsetof((*(*path.Vertex)(nil)).CornerX))},
+		{Type: DataTypeFloat, Size: 1, Offset: int(unsafe.Offsetof((*(*path.Vertex)(nil)).MaxY))},
+		{Type: DataTypeFloat, Size: 2, Offset: int(unsafe.Offsetof((*(*path.Vertex)(nil)).FromX))},
+		{Type: DataTypeFloat, Size: 2, Offset: int(unsafe.Offsetof((*(*path.Vertex)(nil)).CtrlX))},
+		{Type: DataTypeFloat, Size: 2, Offset: int(unsafe.Offsetof((*(*path.Vertex)(nil)).ToX))},
+	})
+	if err != nil {
+		panic(err)
+	}
+	iprogLayout, err := ctx.NewInputLayout(shader_intersect_vert, []InputDesc{
+		{Type: DataTypeFloat, Size: 2, Offset: 0},
+		{Type: DataTypeFloat, Size: 2, Offset: 4 * 2},
+	})
+	if err != nil {
+		panic(err)
+	}
 	return &stenciler{
 		ctx:                ctx,
 		defFBO:             defFBO,
 		prog:               prog,
+		progLayout:         progLayout,
 		iprog:              iprog,
+		iprogLayout:        iprogLayout,
 		uScale:             prog.UniformFor("uniforms.scale"),
 		uOffset:            prog.UniformFor("uniforms.offset"),
 		uPathOffset:        prog.UniformFor("uniforms.pathOffset"),
@@ -201,7 +219,10 @@ func (s *fboSet) delete(ctx Backend, idx int) {
 
 func (s *stenciler) release() {
 	s.fbos.delete(s.ctx, 0)
+	s.progLayout.Release()
 	s.prog.Release()
+	s.iprogLayout.Release()
+	s.iprog.Release()
 	s.indexBuf.Release()
 }
 
@@ -214,6 +235,7 @@ func (c *coverer) release() {
 	for _, p := range c.prog {
 		p.Release()
 	}
+	c.layout.Release()
 }
 
 func buildPath(ctx Backend, p []byte) *pathData {
@@ -271,11 +293,11 @@ func (s *stenciler) begin(sizes []image.Point) {
 	s.fbos.resize(s.ctx, sizes)
 	s.ctx.ClearColor(0.0, 0.0, 0.0, 0.0)
 	s.prog.Bind()
+	s.progLayout.Bind()
 	s.indexBuf.Bind()
 }
 
 func (s *stenciler) stencilPath(bounds image.Rectangle, offset f32.Point, uv image.Point, data *pathData) {
-	data.data.Bind()
 	s.ctx.Viewport(uv.X, uv.Y, bounds.Dx(), bounds.Dy())
 	// Transform UI coordinates to OpenGL coordinates.
 	texSize := f32.Point{X: float32(bounds.Dx()), Y: float32(bounds.Dy())}
@@ -293,11 +315,7 @@ func (s *stenciler) stencilPath(bounds image.Rectangle, offset f32.Point, uv ima
 			batch = max
 		}
 		off := path.VertStride * start * 4
-		s.ctx.SetupVertexArray(attribPathCorner, 2, DataTypeShort, path.VertStride, off+int(unsafe.Offsetof((*(*path.Vertex)(nil)).CornerX)))
-		s.ctx.SetupVertexArray(attribPathMaxY, 1, DataTypeFloat, path.VertStride, off+int(unsafe.Offsetof((*(*path.Vertex)(nil)).MaxY)))
-		s.ctx.SetupVertexArray(attribPathFrom, 2, DataTypeFloat, path.VertStride, off+int(unsafe.Offsetof((*(*path.Vertex)(nil)).FromX)))
-		s.ctx.SetupVertexArray(attribPathCtrl, 2, DataTypeFloat, path.VertStride, off+int(unsafe.Offsetof((*(*path.Vertex)(nil)).CtrlX)))
-		s.ctx.SetupVertexArray(attribPathTo, 2, DataTypeFloat, path.VertStride, off+int(unsafe.Offsetof((*(*path.Vertex)(nil)).ToX)))
+		data.data.BindVertex(path.VertStride, off)
 		s.ctx.DrawElements(DrawModeTriangles, 0, batch*6)
 		start += batch
 	}