[gtk/wip/chergert/macos-iosurface] use backgroundColor to make tiles opaque to compositor

[Christian Hergert <chergert src gnome org>]

commit 9ce369ac500465e34a5a66b7ad1ee49c3892ac29
Author: Christian Hergert <christian hergert me>
Date:   Wed Feb 9 14:19:47 2022 -0800

    use backgroundColor to make tiles opaque to compositor

 gdk/macos/GdkMacosTile.c | 12 ++++++------
 gdk/macos/GdkMacosTile.h |  2 --
 2 files changed, 6 insertions(+), 8 deletions(-)
---
diff --git a/gdk/macos/GdkMacosTile.c b/gdk/macos/GdkMacosTile.c
index 09e82542c2..dd7c84b95d 100644
--- a/gdk/macos/GdkMacosTile.c
+++ b/gdk/macos/GdkMacosTile.c
@@ -29,14 +29,14 @@
   return YES;
 }
 
--(BOOL)isOpaque
-{
-  return self->_opaque;
-}
-
 -(void)setOpaque:(BOOL)opaque
 {
-  self->_opaque = opaque;
+  [super setOpaque:opaque];
+
+  if (opaque)
+    self.backgroundColor = NSColor.blackColor.CGColor;
+  else
+    self.backgroundColor = NSColor.clearColor.CGColor;
 }
 
 -(void)swapBuffer:(IOSurfaceRef)buffer withRect:(CGRect)rect
diff --git a/gdk/macos/GdkMacosTile.h b/gdk/macos/GdkMacosTile.h
index 09295800fb..296a8d7c70 100644
--- a/gdk/macos/GdkMacosTile.h
+++ b/gdk/macos/GdkMacosTile.h
@@ -26,10 +26,8 @@
 
 @interface GdkMacosTile : CALayer
 {
-  guint _opaque : 1;
 };
 
--(void)setOpaque:(BOOL)opaque;
 -(void)swapBuffer:(IOSurfaceRef)buffer withRect:(CGRect)rect;
 
 @end