The documentation on SDL_RenderPresent function states that
"the backbuffer should be considered invalidated after each present",
so copy the entire texture on each redraw.
On the other hand, SDL_UpdateTexture function is described as
"fairly slow function", so restrict it to just the changed pixels.
Also added SDL_RenderClear call, as suggested in the documentation
page on SDL_RenderPresent.
Signed-off-by: Anatoly Trosinenko <anatoly.trosinenko@gmail.com>
---
I managed to reproduce some flicker when using SDL 2D UI (and #if 1)
and it disappeared after this patch. I don't know the original
testcase, though. Hope I correctly calculated the offset. :)
Meanwhile, is it correct to calculate surface_data_offset before assert,
is everything always initialized enough at this point even if assert fails?
ui/sdl2-2d.c | 23 +++++++----------------
1 file changed, 7 insertions(+), 16 deletions(-)
diff --git a/ui/sdl2-2d.c b/ui/sdl2-2d.c
index 8ab68d67b9..1f34817bae 100644
--- a/ui/sdl2-2d.c
+++ b/ui/sdl2-2d.c
@@ -36,6 +36,8 @@ void sdl2_2d_update(DisplayChangeListener *dcl,
struct sdl2_console *scon = container_of(dcl, struct sdl2_console, dcl);
DisplaySurface *surf = qemu_console_surface(dcl->con);
SDL_Rect rect;
+ size_t surface_data_offset = surface_bytes_per_pixel(surf) * x +
+ surface_stride(surf) * y;
assert(!scon->opengl);
@@ -46,27 +48,16 @@ void sdl2_2d_update(DisplayChangeListener *dcl,
return;
}
- /*
- * SDL2 seems to do some double-buffering, and trying to only
- * update the changed areas results in only one of the two buffers
- * being updated. Which flickers alot. So lets not try to be
- * clever do a full update every time ...
- */
-#if 0
rect.x = x;
rect.y = y;
rect.w = w;
rect.h = h;
-#else
- rect.x = 0;
- rect.y = 0;
- rect.w = surface_width(surf);
- rect.h = surface_height(surf);
-#endif
-
- SDL_UpdateTexture(scon->texture, NULL, surface_data(surf),
+
+ SDL_UpdateTexture(scon->texture, &rect,
+ surface_data(surf) + surface_data_offset,
surface_stride(surf));
- SDL_RenderCopy(scon->real_renderer, scon->texture, &rect, &rect);
+ SDL_RenderClear(scon->real_renderer);
+ SDL_RenderCopy(scon->real_renderer, scon->texture, NULL, NULL);
SDL_RenderPresent(scon->real_renderer);
}
--
2.14.1
Ping. Patchwork link: http://patchwork.ozlabs.org/patch/869283/ 2018-02-05 16:32 GMT+03:00 Anatoly Trosinenko <anatoly.trosinenko@gmail.com> : > The documentation on SDL_RenderPresent function states that > "the backbuffer should be considered invalidated after each present", > so copy the entire texture on each redraw. > > On the other hand, SDL_UpdateTexture function is described as > "fairly slow function", so restrict it to just the changed pixels. > > Also added SDL_RenderClear call, as suggested in the documentation > page on SDL_RenderPresent. > > Signed-off-by: Anatoly Trosinenko <anatoly.trosinenko@gmail.com> > --- > I managed to reproduce some flicker when using SDL 2D UI (and #if 1) > and it disappeared after this patch. I don't know the original > testcase, though. Hope I correctly calculated the offset. :) > > Meanwhile, is it correct to calculate surface_data_offset before assert, > is everything always initialized enough at this point even if assert fails? > > ui/sdl2-2d.c | 23 +++++++---------------- > 1 file changed, 7 insertions(+), 16 deletions(-) > > diff --git a/ui/sdl2-2d.c b/ui/sdl2-2d.c > index 8ab68d67b9..1f34817bae 100644 > --- a/ui/sdl2-2d.c > +++ b/ui/sdl2-2d.c > @@ -36,6 +36,8 @@ void sdl2_2d_update(DisplayChangeListener *dcl, > struct sdl2_console *scon = container_of(dcl, struct sdl2_console, > dcl); > DisplaySurface *surf = qemu_console_surface(dcl->con); > SDL_Rect rect; > + size_t surface_data_offset = surface_bytes_per_pixel(surf) * x + > + surface_stride(surf) * y; > > assert(!scon->opengl); > > @@ -46,27 +48,16 @@ void sdl2_2d_update(DisplayChangeListener *dcl, > return; > } > > - /* > - * SDL2 seems to do some double-buffering, and trying to only > - * update the changed areas results in only one of the two buffers > - * being updated. Which flickers alot. So lets not try to be > - * clever do a full update every time ... > - */ > -#if 0 > rect.x = x; > rect.y = y; > rect.w = w; > rect.h = h; > -#else > - rect.x = 0; > - rect.y = 0; > - rect.w = surface_width(surf); > - rect.h = surface_height(surf); > -#endif > - > - SDL_UpdateTexture(scon->texture, NULL, surface_data(surf), > + > + SDL_UpdateTexture(scon->texture, &rect, > + surface_data(surf) + surface_data_offset, > surface_stride(surf)); > - SDL_RenderCopy(scon->real_renderer, scon->texture, &rect, &rect); > + SDL_RenderClear(scon->real_renderer); > + SDL_RenderCopy(scon->real_renderer, scon->texture, NULL, NULL); > SDL_RenderPresent(scon->real_renderer); > } > > -- > 2.14.1 > > -- С уважением, Анатолий Тросиненко e-mail: anatoly.trosinenko@gmail.com
On Wed, Feb 14, 2018 at 09:47:19PM +0300, Anatoly Trosinenko wrote: > Ping. > Patchwork link: http://patchwork.ozlabs.org/patch/869283/ No review comments, patch is perfect ;) Sorry for the delay, was busy with other stuff. Preparing new UI pull request atm, queued the patch. thanks, Gerd
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