gpu/backend: remove clear color and depth state

Specifying the clear color and depth at the time of clearing is
less error prone and a better for modern GPU APIs. As a bonus, we
can get rid of the BufferAttachment type.

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

gpu/backend/backend.go

@@ -27,9 +27,8 @@ type Device interface {
 	NewInputLayout(vertexShader ShaderSources, layout []InputDesc) (InputLayout, error)
 
 	DepthFunc(f DepthFunc)
-	ClearColor(r, g, b, a float32)
 	ClearDepth(d float32)
-	Clear(buffers BufferAttachments)
+	Clear(r, g, b, a float32)
 	Viewport(x, y, width, height int)
 	DrawArrays(mode DrawMode, off, count int)
 	DrawElements(mode DrawMode, off, count int)
@@ -110,8 +109,6 @@ type BlendFactor uint8
 
 type DrawMode uint8
 
-type BufferAttachments uint
-
 type TextureFilter uint8
 type TextureFormat uint8
 
@@ -157,11 +154,6 @@ type Texture interface {
 	Release()
 }
 
-const (
-	BufferAttachmentColor BufferAttachments = 1 << iota
-	BufferAttachmentDepth
-)
-
 const (
 	DepthFuncGreater DepthFunc = iota
 )

gpu/gl/backend.go

@@ -385,23 +385,14 @@ func (b *Backend) Viewport(x, y, width, height int) {
 	b.funcs.Viewport(x, y, width, height)
 }
 
-func (b *Backend) Clear(attachments backend.BufferAttachments) {
-	var mask Enum
-	if attachments&backend.BufferAttachmentColor != 0 {
-		mask |= COLOR_BUFFER_BIT
-	}
-	if attachments&backend.BufferAttachmentDepth != 0 {
-		mask |= DEPTH_BUFFER_BIT
-	}
-	b.funcs.Clear(mask)
+func (b *Backend) Clear(colR, colG, colB, colA float32) {
+	b.funcs.ClearColor(colR, colG, colB, colA)
+	b.funcs.Clear(COLOR_BUFFER_BIT)
 }
 
 func (b *Backend) ClearDepth(d float32) {
 	b.funcs.ClearDepthf(d)
-}
-
-func (b *Backend) ClearColor(colR, colG, colB, colA float32) {
-	b.funcs.ClearColor(colR, colG, colB, colA)
+	b.funcs.Clear(DEPTH_BUFFER_BIT)
 }
 
 func (b *Backend) DepthFunc(f backend.DepthFunc) {

gpu/gpu.go

@@ -335,9 +335,8 @@ func (g *GPU) BeginFrame() {
 	}
 	g.ctx.BindFramebuffer(g.defFBO)
 	g.ctx.DepthFunc(backend.DepthFuncGreater)
-	g.ctx.ClearColor(g.drawOps.clearColor.Float32())
 	g.ctx.ClearDepth(0.0)
-	g.ctx.Clear(backend.BufferAttachmentColor | backend.BufferAttachmentDepth)
+	g.ctx.Clear(g.drawOps.clearColor.Float32())
 	g.ctx.Viewport(0, 0, viewport.X, viewport.Y)
 	g.renderer.drawZOps(g.drawOps.zimageOps)
 	g.zopsTimer.end()
@@ -502,7 +501,7 @@ func (r *renderer) stencilClips(pathCache *opCache, ops []*pathOp) {
 			fbo = p.place.Idx
 			f := r.pather.stenciler.cover(fbo)
 			r.ctx.BindFramebuffer(f.fbo)
-			r.ctx.Clear(backend.BufferAttachmentColor)
+			r.ctx.Clear(0.0, 0.0, 0.0, 0.0)
 		}
 		data, _ := pathCache.get(p.pathKey)
 		r.pather.stencilPath(p.clip, p.off, p.place.Pos, data.(*pathData))
@@ -525,7 +524,7 @@ func (r *renderer) intersect(ops []imageOp) {
 			fbo = img.place.Idx
 			f := r.pather.stenciler.intersections.fbos[fbo]
 			r.ctx.BindFramebuffer(f.fbo)
-			r.ctx.Clear(backend.BufferAttachmentColor)
+			r.ctx.Clear(1.0, 0.0, 0.0, 0.0)
 		}
 		r.ctx.Viewport(img.place.Pos.X, img.place.Pos.Y, img.clip.Dx(), img.clip.Dy())
 		r.intersectPath(img.path, img.clip)

gpu/path.go

@@ -292,7 +292,6 @@ func (s *stenciler) beginIntersect(sizes []image.Point) {
 	// floating point formats. Replace with GL_RGB+GL_UNSIGNED_BYTE if
 	// no floating point support is available.
 	s.intersections.resize(s.ctx, sizes)
-	s.ctx.ClearColor(1.0, 0.0, 0.0, 0.0)
 	s.ctx.BindProgram(s.iprog.prog.prog)
 }
 
@@ -308,7 +307,6 @@ func (s *stenciler) cover(idx int) stencilFBO {
 func (s *stenciler) begin(sizes []image.Point) {
 	s.ctx.BlendFunc(backend.BlendFactorOne, backend.BlendFactorOne)
 	s.fbos.resize(s.ctx, sizes)
-	s.ctx.ClearColor(0.0, 0.0, 0.0, 0.0)
 	s.ctx.BindProgram(s.prog.prog.prog)
 	s.ctx.BindInputLayout(s.prog.layout)
 	s.ctx.BindIndexBuffer(s.indexBuf)