From 1cccb486d48a5d2e7649836b993805bb65dc09e3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Michel=20D=C3=A4nzer?= <mdaenzer@redhat.com>
Date: Tue, 28 Jul 2020 18:40:47 +0200
Subject: [PATCH] present/wnmd: Execute copies at target_msc-1 already

It always takes one update cycle for the copy to become visible on the
host windowing system, so waiting for the target MSC resulted in 1 cycle
delay.

We re-use the idle list for copies which were executed but need their
completion event sent.

Fixes black seams when resizing the "Builder" sub-window of

 GDK_BACKEND=x11 gtk4-demo

on Xwayland (see
https://gitlab.gnome.org/GNOME/mutter/-/issues/1290#note_873557).

Unfortunately, this cannot completely fix the seams with apps which
queue up multiple frames in advance, since there's always at least one
queued frame corresponding to the old window size. But it should at
least help a little in that case as well.

v2:
* Bug fix: Don't update exec_msc in present_wnmd_check_flip_window.
  (Roman Gilg)
* Use exec_msc = target_msc - 1 instead of exec_msc--, and add a
  comment, for clarity.
v3:
* Drop exec_msc = target_msc again in present_wnmd_execute.
* present_execute_copy should never set vblank->queued in
  present_wnmd_execute now, so replace that branch with an assertion.
  (Roman Gilg)

Reviewed-by: Roman Gilg <subdiff@gmail.com>
Tested-by: Roman Gilg <subdiff@gmail.com>
---
 present/present_wnmd.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/present/present_wnmd.c b/present/present_wnmd.c
index 55b2b6463..4ee2585c2 100644
--- a/present/present_wnmd.c
+++ b/present/present_wnmd.c
@@ -222,6 +222,14 @@ present_wnmd_event_notify(WindowPtr window, uint64_t event_id, uint64_t ust, uin
             return;
         }
     }
+
+    /* Copies which were executed but need their completion event sent */
+    xorg_list_for_each_entry(vblank, &window_priv->idle_queue, event_queue) {
+        if (vblank->event_id == event_id) {
+            present_execute_post(vblank, ust, msc);
+            return;
+        }
+    }
 }
 
 void
@@ -369,8 +377,6 @@ present_wnmd_check_flip_window (WindowPtr window)
                                          vblank->sync_flip, vblank->valid, 0, 0, &reason)) {
             vblank->flip = FALSE;
             vblank->reason = reason;
-            if (vblank->sync_flip)
-                vblank->exec_msc = vblank->target_msc;
         }
     }
 }
@@ -470,6 +476,7 @@ present_wnmd_execute(present_vblank_ptr vblank, uint64_t ust, uint64_t crtc_msc)
     vblank->queued = FALSE;
 
     if (vblank->pixmap && vblank->window) {
+        ScreenPtr screen = window->drawable.pScreen;
 
         if (vblank->flip) {
             RegionPtr damage;
@@ -495,7 +502,6 @@ present_wnmd_execute(present_vblank_ptr vblank, uint64_t ust, uint64_t crtc_msc)
             // ask the driver
             if (present_wnmd_flip(vblank->window, vblank->crtc, vblank->event_id,
                                      vblank->target_msc, vblank->pixmap, vblank->sync_flip, damage)) {
-                ScreenPtr screen = window->drawable.pScreen;
                 WindowPtr toplvl_window = present_wnmd_toplvl_pixmap_window(vblank->window);
                 PixmapPtr old_pixmap = screen->GetWindowPixmap(window);
 
@@ -518,7 +524,6 @@ present_wnmd_execute(present_vblank_ptr vblank, uint64_t ust, uint64_t crtc_msc)
               */
             window_priv->flip_pending = NULL;
             vblank->flip = FALSE;
-            vblank->exec_msc = vblank->target_msc;
         }
         DebugPresent(("\tc %p %" PRIu64 ": %08" PRIx32 " -> %08" PRIx32 "\n",
                       vblank, crtc_msc, vblank->pixmap->drawable.id, vblank->window->drawable.id));
@@ -526,9 +531,12 @@ present_wnmd_execute(present_vblank_ptr vblank, uint64_t ust, uint64_t crtc_msc)
         present_wnmd_cancel_flip(window);
 
         present_execute_copy(vblank, crtc_msc);
+        assert(!vblank->queued);
 
-        if (vblank->queued) {
-            xorg_list_add(&vblank->event_queue, &window_priv->exec_queue);
+        if (present_wnmd_queue_vblank(screen, window, vblank->crtc,
+                                      vblank->event_id, crtc_msc + 1)
+            == Success) {
+            xorg_list_add(&vblank->event_queue, &window_priv->idle_queue);
             xorg_list_append(&vblank->window_list, &window_priv->vblank);
 
             return;
@@ -651,8 +659,10 @@ present_wnmd_pixmap(WindowPtr window,
     if (!vblank)
         return BadAlloc;
 
-    if (vblank->flip && vblank->sync_flip)
-        vblank->exec_msc--;
+    /* WNMD presentations always complete (at least) one frame after they
+     * are executed
+     */
+    vblank->exec_msc = vblank->target_msc - 1;
 
     xorg_list_append(&vblank->event_queue, &window_priv->exec_queue);
     vblank->queued = TRUE;