[gtk/wip/chergert/macos-iosurface: 5/7] macos: double buffer IOSurface

[Christian Hergert <chergert src gnome org>]

commit 6016e17a38230165dfb44fcc954f7ded03ea1867
Author: Christian Hergert <christian hergert me>
Date:   Mon Feb 21 23:53:55 2022 -0800

    macos: double buffer IOSurface
    
    It looks like, particularly on the M1, we might need to double buffer the
    contents of the IOSurface<->OpenGL texture bindings. This doesn't appear
    to show up on the Intel macbooks I've tried, but I've seen it in the wild
    on an M1.

 gdk/macos/gdkmacossurface-private.h |  1 +
 gdk/macos/gdkmacossurface.c         | 14 +++++++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)
---
diff --git a/gdk/macos/gdkmacossurface-private.h b/gdk/macos/gdkmacossurface-private.h
index 472058da52..2abc199698 100644
--- a/gdk/macos/gdkmacossurface-private.h
+++ b/gdk/macos/gdkmacossurface-private.h
@@ -47,6 +47,7 @@ struct _GdkMacosSurface
 
   GdkMacosWindow *window;
   GdkMacosBuffer *buffer;
+  GdkMacosBuffer *front;
   GPtrArray *monitors;
   cairo_region_t *opaque_region;
   char *title;
diff --git a/gdk/macos/gdkmacossurface.c b/gdk/macos/gdkmacossurface.c
index 5404d1e3b8..b49f4bb333 100644
--- a/gdk/macos/gdkmacossurface.c
+++ b/gdk/macos/gdkmacossurface.c
@@ -152,6 +152,7 @@ gdk_macos_surface_hide (GdkSurface *surface)
   _gdk_surface_clear_update_area (surface);
 
   g_clear_object (&self->buffer);
+  g_clear_object (&self->front);
 
   if (was_key)
     {
@@ -427,6 +428,9 @@ gdk_macos_surface_destroy (GdkSurface *surface,
 
   g_clear_pointer (&self->monitors, g_ptr_array_unref);
 
+  g_clear_object (&self->buffer);
+  g_clear_object (&self->front);
+
   g_assert (self->sorted.prev == NULL);
   g_assert (self->sorted.next == NULL);
   g_assert (self->frame.prev == NULL);
@@ -781,6 +785,7 @@ _gdk_macos_surface_configure (GdkMacosSurface *self)
       surface->height = content_rect.size.height;
 
       g_clear_object (&self->buffer);
+      g_clear_object (&self->front);
 
       _gdk_surface_update_size (surface);
       gdk_surface_request_layout (surface);
@@ -1032,6 +1037,7 @@ _gdk_macos_surface_monitor_changed (GdkMacosSurface *self)
 
   /* We need to create a new IOSurface for this monitor */
   g_clear_object (&self->buffer);
+  g_clear_object (&self->front);
 
   _gdk_macos_surface_configure (self);
 
@@ -1156,14 +1162,20 @@ void
 _gdk_macos_surface_swap_buffers (GdkMacosSurface      *self,
                                  const cairo_region_t *damage)
 {
+  GdkMacosBuffer *swap;
+
   g_return_if_fail (GDK_IS_MACOS_SURFACE (self));
   g_return_if_fail (damage != NULL);
 
+  swap = self->buffer;
+  self->buffer = self->front;
+  self->front = swap;
+
   /* This code looks like it swaps buffers, but since the IOSurfaceRef
    * appears to be retained on the other side, we really just ask all
    * of the GdkMacosTile CALayer's to update their contents.
    */
-  [self->window swapBuffer:self->buffer withDamage:damage];
+  [self->window swapBuffer:swap withDamage:damage];
 
   /* We might have delayed actually showing the window until the buffer
    * contents are ready to be displayed. Doing so ensures that we don't