graphics: Clear/Fill is now implemented with DrawImage

Only clearing the screen still requires the special method.

image.go

@@ -78,6 +78,18 @@ func (i *Image) Clear() error {
 	return nil
 }
 
+var emptyImage *Image
+
+func init() {
+	const w, h = 16, 16
+	emptyImage, _ = NewImage(w, h, FilterDefault)
+	pix := make([]byte, 4*w*h)
+	for i := range pix {
+		pix[i] = 0xff
+	}
+	emptyImage.ReplacePixels(pix)
+}
+
 // Fill fills the image with a solid color.
 //
 // When the image is disposed, Fill does nothing.
@@ -96,10 +108,26 @@ func (i *Image) Fill(clr color.Color) error {
 
 	i.resolvePendingPixels(false)
 
-	r16, g16, b16, a16 := clr.RGBA()
-	r, g, b, a := uint8(r16>>8), uint8(g16>>8), uint8(b16>>8), uint8(a16>>8)
-	i.mipmap.original().Fill(r, g, b, a)
-	i.disposeMipmaps()
+	r, g, b, a := clr.RGBA()
+	rf, gf, bf, af := 0.0, 0.0, 0.0, 0.0
+	if a > 0 {
+		rf = float64(r) / float64(a)
+		gf = float64(g) / float64(a)
+		bf = float64(b) / float64(a)
+		af = float64(a) / 0xffff
+	}
+
+	sw, sh := emptyImage.Size()
+	dw, dh := i.Size()
+
+	op := &DrawImageOptions{}
+	op.GeoM.Scale(float64(dw)/float64(sw), float64(dh)/float64(sh))
+	op.ColorM.Scale(rf, gf, bf, af)
+	// TODO: Use the previous composite mode if possible.
+	if af < 1.0 {
+		op.CompositeMode = CompositeModeCopy
+	}
+	i.DrawImage(emptyImage, op)
 	return nil
 }
 

internal/shareable/shareable.go

@@ -299,18 +299,17 @@ func (i *Image) DrawTriangles(img *Image, vertices []float32, indices []uint16,
 	}
 }
 
-// Fill fills the image with a color. This affects not only the (0, 0)-(width, height) region but also the whole
-// framebuffer region.
-func (i *Image) Fill(r, g, b, a uint8) {
+// ClearFramebuffer clears the image with a color. This affects not only the (0, 0)-(width, height) region but also
+// the whole framebuffer region.
+func (i *Image) ClearFramebuffer() {
 	backendsM.Lock()
+	defer backendsM.Unlock()
 	if i.disposed {
 		panic("shareable: the drawing target image must not be disposed (Fill)")
 	}
 	i.ensureNotShared()
 
-	i.backend.restorable.Fill(r, g, b, a)
-
-	backendsM.Unlock()
+	i.backend.restorable.Fill(0, 0, 0, 0)
 }
 
 func (i *Image) ReplacePixels(p []byte) {

uicontext.go

@@ -111,7 +111,7 @@ func (c *uiContext) Update(afterFrameUpdate func()) error {
 	}
 
 	// This clear is needed for fullscreen mode or some mobile platforms (#622).
-	c.screen.Clear()
+	c.screen.mipmap.orig.ClearFramebuffer()
 
 	op := &DrawImageOptions{}