internal/graphicsdriver/metal: Skip clearing the screen on Metal

internal/driver/graphics.go

@@ -45,6 +45,7 @@ type Graphics interface {
 	SetVsyncEnabled(enabled bool)
 	FramebufferYDirection() YDirection
 	NeedsRestoring() bool
+	NeedsClearingScreen() bool
 	IsGL() bool
 	HasHighPrecisionFloat() bool
 	MaxImageSize() int

internal/graphicsdriver/metal/graphics.go

@@ -794,7 +794,11 @@ func (g *Graphics) draw(rps mtl.RenderPipelineState, dst *Image, dstRegion drive
 		rpd := mtl.RenderPassDescriptor{}
 		// Even though the destination pixels are not used, mtl.LoadActionDontCare might cause glitches
 		// (#1019). Always using mtl.LoadActionLoad is safe.
+		if dst.screen {
+			rpd.ColorAttachments[0].LoadAction = mtl.LoadActionClear
+		} else {
 			rpd.ColorAttachments[0].LoadAction = mtl.LoadActionLoad
+		}
 		rpd.ColorAttachments[0].StoreAction = mtl.StoreActionStore
 
 		t := dst.mtlTexture()
@@ -1015,6 +1019,10 @@ func (g *Graphics) NeedsRestoring() bool {
 	return false
 }
 
+func (g *Graphics) NeedsClearingScreen() bool {
+	return false
+}
+
 func (g *Graphics) IsGL() bool {
 	return false
 }

internal/graphicsdriver/opengl/graphics.go

@@ -337,6 +337,10 @@ func (g *Graphics) NeedsRestoring() bool {
 	return g.context.needsRestoring()
 }
 
+func (g *Graphics) NeedsClearingScreen() bool {
+	return true
+}
+
 func (g *Graphics) IsGL() bool {
 	return true
 }

uicontext.go

@@ -205,8 +205,10 @@ func (c *uiContext) updateImpl(updateCount int) error {
 	}
 	c.game.Draw(c.offscreen)
 
+	if uiDriver().Graphics().NeedsClearingScreen() {
 		// This clear is needed for fullscreen mode or some mobile platforms (#622).
 		c.screen.Clear()
+	}
 
 	op := &DrawImageOptions{}