From df3b03e05b5c826584fc75466f404b53844edcf4 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Thu, 5 Feb 2015 14:11:40 -0500
Subject: [PATCH] present: make unflip work when the flip window is destroyed
 or clipped

Present allows a window to redirect itself to a client provided buffer.

If that buffer is about to be invalidated, the window needs to direct
itself back to its original buffer (some part of the root window/front
buffer), and update that storage to have a current contents (a process
called "unflipping").

The present_unflip finds the original buffer by way of the drawable
associated with the window presented to.  If the window is already
destroyed, then it get dissociated from its drawable, and the copy
operation used to update the original buffer fails.

When the compositor exits its buffers become invalidated and the
composite overlay window gets destroyed at the same time.  This leads
to a temporary flash of the root window as it looked at the time
the X server was started.

The present_unflip function performs the copy using the clip list of
the window presented to. If the window is clipped, the copy operation
used to update the original buffer will be clipped as well.

When VT switching away the X server sets the clip to 0, so that
applications get fully reexposed the next time the VT is active.

When VT switching the present_unflip function is called.  This leads
to a temporary flash of the root window as it looked at the time
the X server was started.

This commit changes present_flip to update the front buffer directly,
rather than by way of the drawable associated with the window presented
to.  At the same time, doing this means avoiding the clip list
associated with the window.
---
 present/present.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/present/present.c b/present/present.c
index 8e4829e..a516575 100644
--- a/present/present.c
+++ b/present/present.c
@@ -377,74 +377,74 @@ present_set_tree_pixmap(WindowPtr window, PixmapPtr pixmap)
 
     visit.old = (*screen->GetWindowPixmap)(window);
     visit.new = pixmap;
     if (visit.old == visit.new)
         return;
     TraverseTree(window, present_set_tree_pixmap_visit, &visit);
 }
 
 static void
 present_set_abort_flip(ScreenPtr screen)
 {
     present_screen_priv_ptr screen_priv = present_screen_priv(screen);
 
     /* Switch back to using the screen pixmap now to avoid
      * 2D applications drawing to the wrong pixmap.
      */
 
     if (screen_priv->flip_window)
         present_set_tree_pixmap(screen_priv->flip_window,
                                   (*screen->GetScreenPixmap)(screen));
 
     present_set_tree_pixmap(screen->root, (*screen->GetScreenPixmap)(screen));
 
     screen_priv->flip_pending->abort_flip = TRUE;
 }
 
 static void
 present_unflip(ScreenPtr screen)
 {
     present_screen_priv_ptr screen_priv = present_screen_priv(screen);
+    PixmapPtr pixmap = (*screen->GetScreenPixmap)(screen);
 
     assert (!screen_priv->unflip_event_id);
     assert (!screen_priv->flip_pending);
 
     if (screen_priv->flip_window)
-        present_set_tree_pixmap(screen_priv->flip_window,
-                                  (*screen->GetScreenPixmap)(screen));
+        present_set_tree_pixmap(screen_priv->flip_window, pixmap);
 
-    present_set_tree_pixmap(screen->root, (*screen->GetScreenPixmap)(screen));
+    present_set_tree_pixmap(screen->root, pixmap);
 
     /* Update the screen pixmap with the current flip pixmap contents
      */
     if (screen_priv->flip_pixmap && screen_priv->flip_window) {
-        present_copy_region(&screen_priv->flip_window->drawable,
+        present_copy_region(&pixmap->drawable,
                             screen_priv->flip_pixmap,
                             NULL, 0, 0);
     }
     screen_priv->unflip_event_id = ++present_event_id;
     DebugPresent(("u %lld\n", screen_priv->unflip_event_id));
     (*screen_priv->info->unflip) (screen, screen_priv->unflip_event_id);
 }
 
 static void
 present_flip_notify(present_vblank_ptr vblank, uint64_t ust, uint64_t crtc_msc)
 {
     ScreenPtr                   screen = vblank->screen;
     present_screen_priv_ptr     screen_priv = present_screen_priv(screen);
 
     DebugPresent(("\tn %lld %p %8lld: %08lx -> %08lx\n",
                   vblank->event_id, vblank, vblank->target_msc,
                   vblank->pixmap ? vblank->pixmap->drawable.id : 0,
                   vblank->window ? vblank->window->drawable.id : 0));
 
     assert (vblank == screen_priv->flip_pending);
 
     present_flip_idle(screen);
 
     xorg_list_del(&vblank->event_queue);
 
     /* Transfer reference for pixmap and fence from vblank to screen_priv */
     screen_priv->flip_crtc = vblank->crtc;
     screen_priv->flip_window = vblank->window;
     screen_priv->flip_serial = vblank->serial;
     screen_priv->flip_pixmap = vblank->pixmap;
-- 
2.1.0