gdi32: Track ticks since draw start per window_surface.

Track ticks since draw start per window_surface, instead of per DC as is currently the case. This change helps reduce visual glitches caused by badly timed flushes when drawing to the same window_surface from multiple DCs (e.g., for child windows). This approach is a better fit for the current heuristic for forcing flushing, which consults the shared window_surface bounds to decide whether this is the start of a draw in order to reset the (currently per DC) draw start time. The problem in the current implementation occurs when a drawing to a DC begins with an already damaged window_surface, e.g., due to draws from other DCs targeting that window_surface. In such a case, the DC draw start time is not reset and refers to the start of some previous draw sequence using this DC, thus increasing the chances that the 50ms time flush limit will be eventually exceeded in the middle of the current draw sequence. In other words, the state of the (shared) window_surface damage is not a reliable indicator of the beginning (or not) of a draw to a DC. An example, assuming DC1 and DC2 target the same window_surface: DC1.start_ticks = 0 DC2.start_ticks = 0 FLUSH_PERIOD = 50 0 flush 1 draw to DC1 -> DC1.start_ticks = 1 ... [no flush] ... 2 draw to DC2 -> DC2.start_ticks remains 0 since surface is damaged ... 50 flush 51 draw to DC1 -> DC1.start_ticks = 51 ... [no flush] ... 52 draw to DC2 -> DC2.start_ticks remains 0 since surface is damaged, current - DC2.start_ticks > FLUSH_PERIOD so we are forced to flush in the middle of the drawing sequence => potential glitch Tracking the draw start per window_surface ameliorates the problem because the beginning of a draw on a DC targeting an undamaged window_surface resets the start time for all DCs targeting that window_surface: ... 50 flush 51 draw to DC1 -> surface.draw_ticks = 51 ... [no flush] ... 52 draw to DC2 -> surface.draw_ticks remains 51 since surface is damaged, but current - surface.draw_ticks < FLUSH_PERIOD, so we do not flush Signed-off-by: Alexandros Frantzis <alexandros.frantzis@collabora.com>

gdi32: Track ticks since draw start per window_surface.
aa72d7d4 · Alexandros Frantzis · Alexandre Julliard · c9285f32 · aa72d7d4 · aa72d7d4
Commit aa72d7d4 authored Feb 16, 2023 by Alexandros Frantzis Committed by Alexandre Julliard Feb 21, 2023
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dc.c dlls/win32u/dibdrv/dc.c +3 -3

gdi_driver.h include/wine/gdi_driver.h +1 -0

No files found.
--- a/dlls/win32u/dibdrv/dc.c
+++ b/dlls/win32u/dibdrv/dc.c
@@ -731,7 +731,6 @@ struct windrv_physdev
    struct gdi_physdev     dev;
    struct dibdrv_physdev *dibdrv;
    struct window_surface *surface;
-    DWORD                  start_ticks;
 };

 static const struct gdi_dc_funcs window_driver;
@@ -745,13 +744,14 @@ static inline void lock_surface( struct windrv_physdev *dev )
 {
    /* gdi_lock should not be locked */
    dev->surface->funcs->lock( dev->surface );
-    if (IsRectEmpty( dev->dibdrv->bounds )) dev->start_ticks = NtGetTickCount();
+    if (IsRectEmpty( dev->dibdrv->bounds )) dev->surface->draw_start_ticks = NtGetTickCount();
 }

 static inline void unlock_surface( struct windrv_physdev *dev )
 {
+    BOOL should_flush = NtGetTickCount() - dev->surface->draw_start_ticks > FLUSH_PERIOD;
    dev->surface->funcs->unlock( dev->surface );
-    if (NtGetTickCount() - dev->start_ticks > FLUSH_PERIOD) dev->surface->funcs->flush( dev->surface );
+    if (should_flush) dev->surface->funcs->flush( dev->surface );
 }

 static void CDECL unlock_bits_surface( struct gdi_image_bits *bits )

--- a/include/wine/gdi_driver.h
+++ b/include/wine/gdi_driver.h
@@ -217,6 +217,7 @@ struct window_surface
    struct list                        entry; /* entry in global list managed by user32 */
    LONG                               ref;   /* reference count */
    RECT                               rect;  /* constant, no locking needed */
+    DWORD                              draw_start_ticks; /* start ticks of fresh draw */
    /* driver-specific fields here */
 };