gpu,widget,op/paint,gpu: remove support for ImageOp.Rect

This is effectively a revert of commit gioui.org/commit/69dfd2e3a5541.

ImageOp.Rect is the wrong abstraction; it implies a clipping operation that is
better handled by package clip.

API change. Uses of ImageOp.Rect should apply a clip.Rect before the PaintOp,
or use image.RGBA.SubImage (or similar).

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

gpu/gpu.go

@@ -130,7 +130,6 @@ type clipOp struct {
 
 // imageOpData is the shadow of paint.ImageOp.
 type imageOpData struct {
-	rect   image.Rectangle
 	src    *image.RGBA
 	handle interface{}
 }
@@ -170,18 +169,7 @@ func decodeImageOp(data []byte, refs []interface{}) imageOpData {
 	if handle == nil {
 		return imageOpData{}
 	}
-	bo := binary.LittleEndian
 	return imageOpData{
-		rect: image.Rectangle{
-			Min: image.Point{
-				X: int(int32(bo.Uint32(data[1:]))),
-				Y: int(int32(bo.Uint32(data[5:]))),
-			},
-			Max: image.Point{
-				X: int(int32(bo.Uint32(data[9:]))),
-				Y: int(int32(bo.Uint32(data[13:]))),
-			},
-		},
 		src:    refs[0].(*image.RGBA),
 		handle: handle,
 	}
@@ -962,7 +950,12 @@ func (d *drawState) materialFor(cache *resourceCache, rect f32.Rectangle, off f3
 		m.material = materialTexture
 		dr := boundRectF(rect.Add(off))
 		sz := d.image.src.Bounds().Size()
-		sr := layout.FRect(d.image.rect)
+		sr := f32.Rectangle{
+			Max: f32.Point{
+				X: float32(sz.X),
+				Y: float32(sz.Y),
+			},
+		}
 		if dx := float32(dr.Dx()); dx != 0 {
 			// Don't clip 1 px width sources.
 			if sdx := sr.Dx(); sdx > 1 {