[gtk/wip/chergert/macos-iosurface: 1/2] macos: add comment about purging IOSurface

[Christian Hergert <chergert src gnome org>]

commit 89922c70319003b8394bafc4b5cd6c4f90cd3c32
Author: Christian Hergert <christian hergert me>
Date:   Sat Feb 12 02:32:20 2022 -0800

    macos: add comment about purging IOSurface

 gdk/macos/gdkmacosbuffer.c | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/gdk/macos/gdkmacosbuffer.c b/gdk/macos/gdkmacosbuffer.c
index 2982d39594..ac99302ee4 100644
--- a/gdk/macos/gdkmacosbuffer.c
+++ b/gdk/macos/gdkmacosbuffer.c
@@ -52,6 +52,12 @@ gdk_macos_buffer_dispose (GObject *object)
     g_critical ("Attempt to dispose %s while lock is held",
                 G_OBJECT_TYPE_NAME (self));
 
+  /* We could potentially force the unload of our surface here with
+   * IOSurfaceSetPurgeable (self->surface, kIOSurfacePurgeableEmpty, NULL)
+   * but that would cause it to empty when the layers may still be attached
+   * to it. Better to just let it get GC'd by the system after they have
+   * moved on to a new buffer.
+   */
   g_clear_pointer (&self->surface, CFRelease);
   g_clear_pointer (&self->damage, cairo_region_destroy);