better cursor capture

Overlord-Client/cmd/agent/capture/win_duplication.go

@@ -612,6 +612,7 @@ type duplicationState struct {
 	lastFrame     *image.RGBA
 	lastFrameAt   time.Time
 	lastFail      time.Time
+	cursorScratch *image.RGBA
 }
 
 func SetDesktopDuplication(enabled bool) {
@@ -673,6 +674,7 @@ func (s *duplicationState) closeLocked() {
 	s.lastBase = nil
 	s.lastFrame = nil
 	s.lastFrameAt = time.Time{}
+	s.cursorScratch = nil
 }
 
 func (s *duplicationState) capture(display int) (*image.RGBA, error) {
@@ -767,7 +769,8 @@ func (s *duplicationState) composeFrame(base *image.RGBA) *image.RGBA {
 
 	img := base
 	if withCursor {
-		img = cloneRGBA(base)
+		img = s.ensureCursorScratch(base.Rect)
+		copy(img.Pix, base.Pix)
 	}
 	bounds := s.bounds
 	if bounds.Dx() != int(s.desc.ModeDesc.Width) || bounds.Dy() != int(s.desc.ModeDesc.Height) {
@@ -787,6 +790,13 @@ func (s *duplicationState) composeFrame(base *image.RGBA) *image.RGBA {
 	return img
 }
 
+func (s *duplicationState) ensureCursorScratch(rect image.Rectangle) *image.RGBA {
+	if s.cursorScratch == nil || s.cursorScratch.Rect != rect {
+		s.cursorScratch = image.NewRGBA(rect)
+	}
+	return s.cursorScratch
+}
+
 func cloneRGBA(src *image.RGBA) *image.RGBA {
 	if src == nil {
 		return nil