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>

app/headless/backend_test.go

@@ -110,12 +110,10 @@ func TestFramebuffers(t *testing.T) {
 		col2 = color.RGBA{R: 0xfe, G: 0xba, B: 0xbe, A: 0xca}
 	)
 	fcol1, fcol2 := f32color.RGBAFromSRGB(col1), f32color.RGBAFromSRGB(col2)
-	b.ClearColor(fcol1.Float32())
 	b.BindFramebuffer(fbo1)
-	b.Clear(backend.BufferAttachmentColor)
-	b.ClearColor(fcol2.Float32())
+	b.Clear(fcol1.Float32())
 	b.BindFramebuffer(fbo2)
-	b.Clear(backend.BufferAttachmentColor)
+	b.Clear(fcol2.Float32())
 	img := screenshot(t, fbo1, sz)
 	if got := img.RGBAAt(0, 0); got != col1 {
 		t.Errorf("got color %v, expected %v", got, col1)
@@ -129,7 +127,11 @@ func TestFramebuffers(t *testing.T) {
 func setupFBO(t *testing.T, b backend.Device, size image.Point) backend.Framebuffer {
 	fbo := newFBO(t, b, size)
 	b.BindFramebuffer(fbo)
-	b.Clear(backend.BufferAttachmentColor | backend.BufferAttachmentDepth)
+	// ClearColor accepts linear RGBA colors, while 8-bit colors
+	// are in the sRGB color space.
+	col := f32color.RGBAFromSRGB(clearCol)
+	b.Clear(col.Float32())
+	b.ClearDepth(0.0)
 	b.Viewport(0, 0, size.X, size.Y)
 	return fbo
 }
@@ -172,10 +174,6 @@ func newBackend(t *testing.T) backend.Device {
 		t.Fatal(err)
 	}
 	b.BeginFrame()
-	// ClearColor accepts linear RGBA colors, while 8-bit colors
-	// are in the sRGB color space.
-	col := f32color.RGBAFromSRGB(clearCol)
-	b.ClearColor(col.Float32())
 	t.Cleanup(func() {
 		b.EndFrame()
 		ctx.ReleaseCurrent()

app/internal/d3d11/backend_windows.go

@@ -10,7 +10,6 @@ import (
 	"unsafe"
 
 	"gioui.org/gpu/backend"
-	"gioui.org/internal/f32color"
 	gunsafe "gioui.org/internal/unsafe"
 	"golang.org/x/sys/windows"
 )
@@ -27,8 +26,8 @@ type Device struct {
 }
 
 type Backend struct {
-	clearColor f32color.RGBA
-	clearDepth float32
+	// Temporary storage to avoid garbage.
+	clearColor [4]float32
 	viewport   _D3D11_VIEWPORT
 	depthState depthState
 	blendState blendState
@@ -539,16 +538,14 @@ func (b *Backend) NewProgram(vertexShader, fragmentShader backend.ShaderSources)
 	return p, nil
 }
 
-func (b *Backend) ClearColor(colr, colg, colb, cola float32) {
-	b.clearColor = f32color.RGBA{R: colr, G: colg, B: colb, A: cola}
+func (b *Backend) Clear(colr, colg, colb, cola float32) {
+	b.clearColor = [4]float32{colr, colg, colb, cola}
+	b.dev.ctx.ClearRenderTargetView(b.fbo.renderTarget, &b.clearColor)
 }
 
-func (b *Backend) Clear(buffers backend.BufferAttachments) {
-	if buffers&backend.BufferAttachmentColor != 0 {
-		b.dev.ctx.ClearRenderTargetView(b.fbo.renderTarget, &b.clearColor)
-	}
-	if buffers&backend.BufferAttachmentDepth != 0 && b.fbo.depthView != nil {
-		b.dev.ctx.ClearDepthStencilView(b.fbo.depthView, _D3D11_CLEAR_DEPTH|_D3D11_CLEAR_STENCIL, b.clearDepth, 0)
+func (b *Backend) ClearDepth(depth float32) {
+	if b.fbo.depthView != nil {
+		b.dev.ctx.ClearDepthStencilView(b.fbo.depthView, _D3D11_CLEAR_DEPTH|_D3D11_CLEAR_STENCIL, depth, 0)
 	}
 }
 
@@ -650,10 +647,6 @@ func (b *Backend) DepthFunc(f backend.DepthFunc) {
 	b.depthState.fn = f
 }
 
-func (b *Backend) ClearDepth(d float32) {
-	b.clearDepth = d
-}
-
 func (b *Backend) SetBlend(enable bool) {
 	b.blendState.enable = enable
 }

app/internal/d3d11/d3d11_windows.go

@@ -1034,7 +1034,7 @@ func (c *_ID3D11DeviceContext) ClearDepthStencilView(target *_ID3D11DepthStencil
 	)
 }
 
-func (c *_ID3D11DeviceContext) ClearRenderTargetView(target *_ID3D11RenderTargetView, color *f32color.RGBA) {
+func (c *_ID3D11DeviceContext) ClearRenderTargetView(target *_ID3D11RenderTargetView, color *[4]float32) {
 	syscall.Syscall(
 		c.vtbl.ClearRenderTargetView,
 		3,