5 files changed, 35 insertions(+), 6 deletions(-)

M app/headless/headless.go
M app/loop.go
M gpu/compute.go
M gpu/gpu.go
M internal/rendertest/util_test.go

@@ 6,6 6,7 @@ package headless
 
 import (
 	"image"
+	"image/color"
 	"runtime"
 
 	"gioui.org/gpu"


@@ 108,6 109,7 @@ func (w *Window) Release() {
 // operation list.
 func (w *Window) Frame(frame *op.Ops) error {
 	return contextDo(w.ctx, func() error {
+		w.gpu.Clear(color.NRGBA{A: 0xff, R: 0xff, G: 0xff, B: 0xff})
 		w.gpu.Collect(w.size, frame)
 		return w.gpu.Frame()
 	})

@@ 4,6 4,7 @@ package app
 
 import (
 	"image"
+	"image/color"
 	"runtime"
 
 	"gioui.org/app/internal/window"


@@ 85,6 86,7 @@ func (l *renderLoop) renderLoop(ctx window.Context) error {
 				l.refreshErr <- ctx.MakeCurrent()
 			case frame := <-l.frames:
 				ctx.Lock()
+				g.Clear(color.NRGBA{A: 0xff, R: 0xff, G: 0xff, B: 0xff})
 				g.Collect(frame.viewport, frame.ops)
 				// Signal that we're done with the frame ops.
 				l.ack <- struct{}{}

@@ 230,6 230,11 @@ func (g *compute) Collect(viewport image.Point, ops *op.Ops) {
 	}
 }
 
+func (g *compute) Clear(col color.NRGBA) {
+	g.drawOps.clear = true
+	g.drawOps.clearColor = f32color.LinearFromSRGB(col)
+}
+
 func (g *compute) Frame() error {
 	viewport := g.drawOps.viewport
 	tileDims := image.Point{


@@ 285,8 290,11 @@ func (g *compute) encode(viewport image.Point) {
 	// Flip Y-axis.
 	flipY := f32.Affine2D{}.Scale(f32.Pt(0, 0), f32.Pt(1, -1)).Offset(f32.Pt(0, float32(viewport.Y)))
 	g.enc.transform(flipY)
-	g.enc.rect(f32.Rectangle{Max: layout.FPt(viewport)}, false)
-	g.enc.fill(f32color.NRGBAToRGBA(g.drawOps.clearColor.SRGB()))
+	if g.drawOps.clear {
+		g.drawOps.clear = false
+		g.enc.rect(f32.Rectangle{Max: layout.FPt(viewport)}, false)
+		g.enc.fill(f32color.NRGBAToRGBA(g.drawOps.clearColor.SRGB()))
+	}
 	g.encodeOps(flipY, viewport, g.drawOps.allImageOps)
 }
 

@@ 31,9 31,17 @@ import (
 )
 
 type GPU interface {
+	// Release non-Go resources. The GPU is no longer valid after Release.
 	Release()
-	Collect(viewport image.Point, frameOps *op.Ops)
+	// Clear sets the clear color for the next Frame.
+	Clear(color color.NRGBA)
+	// Collect the graphics operations from frame, given the viewport.
+	Collect(viewport image.Point, frame *op.Ops)
+	// Frame clears the color buffer and draws the collected operations.
 	Frame() error
+	// Profile returns the last available profiling information. Profiling
+	// information is requested when Collect sees a ProfileOp, and the result
+	// is available through Profile at some later time.
 	Profile() string
 }
 


@@ 65,6 73,7 @@ type drawOps struct {
 	cache      *resourceCache
 	vertCache  []byte
 	viewport   image.Point
+	clear      bool
 	clearColor f32color.RGBA
 	// allImageOps is the combined list of imageOps and
 	// zimageOps, in drawing order.


@@ 404,6 413,11 @@ func (g *gpu) init(ctx backend.Device) error {
 	return nil
 }
 
+func (g *gpu) Clear(col color.NRGBA) {
+	g.drawOps.clear = true
+	g.drawOps.clearColor = f32color.LinearFromSRGB(col)
+}
+
 func (g *gpu) Release() {
 	g.renderer.release()
 	g.drawOps.pathCache.release()


@@ 442,7 456,10 @@ func (g *gpu) Frame() error {
 	g.ctx.DepthFunc(backend.DepthFuncGreater)
 	// Note that Clear must be before ClearDepth if nothing else is rendered
 	// (len(zimageOps) == 0). If not, the Fairphone 2 will corrupt the depth buffer.
-	g.ctx.Clear(g.drawOps.clearColor.Float32())
+	if g.drawOps.clear {
+		g.drawOps.clear = false
+		g.ctx.Clear(g.drawOps.clearColor.Float32())
+	}
 	g.ctx.ClearDepth(0.0)
 	g.ctx.Viewport(0, 0, viewport.X, viewport.Y)
 	g.renderer.drawZOps(g.cache, g.drawOps.zimageOps)


@@ 799,7 816,6 @@ func floor(v float32) int {
 
 func (d *drawOps) reset(cache *resourceCache, viewport image.Point) {
 	d.profile = false
-	d.clearColor = f32color.RGBA{R: 1.0, G: 1.0, B: 1.0, A: 1.0}
 	d.cache = cache
 	d.viewport = viewport
 	d.imageOps = d.imageOps[:0]


@@ 1006,6 1022,7 @@ loop:
 				d.imageOps = d.imageOps[:0]
 				z = 0
 				d.clearColor = mat.color.Opaque()
+				d.clear = true
 				continue
 			}
 			z++

@@ 161,7 161,7 @@ func verifyRef(t *testing.T, img *image.RGBA, frame int) (ok bool) {
 	}
 	ref, ok := r.(*image.RGBA)
 	if !ok {
-		t.Error("ref image note RGBA")
+		t.Errorf("image is a %T, expected *image.RGBA", r)
 		return
 	}
 	if len(ref.Pix) != len(img.Pix) {