present: Make window MSC offset 0 initially

The MSC offset used by a window is adjusted as the window moves
between screens, and between shown/unshown. The value shouldn't
matter, but it's helpful for debugging to have window MSC values be
the same as the CRTC MSC at first.

This patch introduces a unique CRTC value so that Present can detect
the first time a window is a PresentPixmap destination and set the MSC
offset to zero, rather than using the fake MSC value as the previous
window MSC.

Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Eric Anholt <eric@anholt.net>

1 files changed, 11 insertions, 7 deletions

diff --git a/present/present.c b/present/present.c
index 3aea0d7c6..f624e5b7b 100644
--- a/present/present.c
+++ b/present/present.c
@@ -291,14 +291,18 @@ present_window_to_crtc_msc(WindowPtr window, RRCrtcPtr crtc, uint64_t window_msc
     if (crtc != window_priv->crtc) {
         uint64_t        old_ust, old_msc;
 
-        /* The old CRTC may have been turned off, in which case
-         * we'll just use whatever previous MSC we'd seen from this CRTC
-         */
+        if (window_priv->crtc == PresentCrtcNeverSet) {
+            window_priv->msc_offset = 0;
+        } else {
+            /* The old CRTC may have been turned off, in which case
+             * we'll just use whatever previous MSC we'd seen from this CRTC
+             */
 
-        if (present_get_ust_msc(window->drawable.pScreen, window_priv->crtc, &old_ust, &old_msc) != Success)
-            old_msc = window_priv->msc;
+            if (present_get_ust_msc(window->drawable.pScreen, window_priv->crtc, &old_ust, &old_msc) != Success)
+                old_msc = window_priv->msc;
 
-        window_priv->msc_offset += new_msc - old_msc;
+            window_priv->msc_offset += new_msc - old_msc;
+        }
         window_priv->crtc = crtc;
     }
 
@@ -725,7 +729,7 @@ present_pixmap(WindowPtr window,
         if (!pixmap)
             target_crtc = window_priv->crtc;
 
-        if (!target_crtc)
+        if (!target_crtc || target_crtc == PresentCrtcNeverSet)
             target_crtc = present_get_crtc(window);
     }