[gtk/wip/chergert/for-macos-1] macos: add helper to check if surface is opaque

[Christian Hergert <chergert src gnome org>]

commit 3c9687fcf1efb5f999320b1130d824b70c0d2283
Author: Christian Hergert <christian hergert me>
Date:   Mon Feb 14 02:18:51 2022 -0800

    macos: add helper to check if surface is opaque

 gdk/macos/gdkmacossurface-private.h |  1 +
 gdk/macos/gdkmacossurface.c         | 21 +++++++++++++++++++++
 2 files changed, 22 insertions(+)
---
diff --git a/gdk/macos/gdkmacossurface-private.h b/gdk/macos/gdkmacossurface-private.h
index ccb8a83179..61ea1ba00d 100644
--- a/gdk/macos/gdkmacossurface-private.h
+++ b/gdk/macos/gdkmacossurface-private.h
@@ -131,6 +131,7 @@ void               _gdk_macos_surface_set_opacity             (GdkMacosSurface
 void               _gdk_macos_surface_get_root_coords         (GdkMacosSurface    *self,
                                                                int                *x,
                                                                int                *y);
+gboolean           _gdk_macos_surface_is_opaque               (GdkMacosSurface      *self);
 
 G_END_DECLS
 
diff --git a/gdk/macos/gdkmacossurface.c b/gdk/macos/gdkmacossurface.c
index a2c7bb485d..42ac59d059 100644
--- a/gdk/macos/gdkmacossurface.c
+++ b/gdk/macos/gdkmacossurface.c
@@ -603,6 +603,27 @@ _gdk_macos_surface_get_shadow (GdkMacosSurface *self,
     *right = self->shadow_right;
 }
 
+gboolean
+_gdk_macos_surface_is_opaque (GdkMacosSurface *self)
+{
+  g_return_val_if_fail (GDK_IS_MACOS_SURFACE (self), FALSE);
+
+  if (self->opaque_region != NULL &&
+      cairo_region_num_rectangles (self->opaque_region) == 1)
+    {
+      cairo_rectangle_int_t extents;
+
+      cairo_region_get_extents (self->opaque_region, &extents);
+
+      return (extents.x == 0 &&
+              extents.y == 0 &&
+              extents.width == GDK_SURFACE (self)->width &&
+              extents.height == GDK_SURFACE (self)->height);
+    }
+
+  return FALSE;
+}
+
 const char *
 _gdk_macos_surface_get_title (GdkMacosSurface *self)
 {