Optimize dirty rectangle rendering.

Only push the video surface to a texture immediately when the app does SDL_Flip() or SDL_UpdateRect(0,0,0,0). If it looks like dirty rectangle rendering, only push when we're in a PumpEvents that's close to 60Hz, under the assumption that the app isn't in the middle of rendering if they're pumping the event queue, and that updates to the texture faster than the refresh rate aren't seen anyhow. This lets things that render a little in response to every mouse event, like TuxPaint, run at reasonable speeds and still look correct. This probably needs to not hardcode for 60Hz, but get the actual refresh rate from SDL2.
libsdl-org · Mar 6, 2019 · 5ee36c8 · 5ee36c8
1 parent 7c1b74c
commit 5ee36c8
Showing 1 changed file with 11 additions and 7 deletions.
diff --git a/src/SDL12_compat.c b/src/SDL12_compat.c
@@ -718,7 +718,8 @@ static SDL_Window *VideoWindow20 = NULL;
 static SDL_Renderer *VideoRenderer20 = NULL;
 static SDL_Texture *VideoTexture20 = NULL;
 static SDL12_Surface *VideoSurface12 = NULL;
-static SDL_bool VideoSurfaceUpdated = SDL_FALSE;
+static Uint32 VideoSurfacePresentTicks = 0;
+static Uint32 VideoSurfaceLastPresentTicks = 0;
 static SDL_Surface *VideoConvertSurface20 = NULL;
 static SDL_GLContext *VideoGLContext20 = NULL;
 static char *WindowTitle = NULL;
@@ -2855,7 +2856,8 @@ SDL_SetVideoMode(int width, int height, int bpp, Uint32 flags12)
 
     FIXME("setup screen saver");
 
-    VideoSurfaceUpdated = SDL_FALSE;
+    VideoSurfacePresentTicks = 0;
+    VideoSurfaceLastPresentTicks = 0;
 
     return VideoSurface12;
 }
@@ -3118,7 +3120,8 @@ PresentScreen(void)
     SDL20_UnlockTexture(VideoTexture20);
     SDL20_RenderCopy(VideoRenderer20, VideoTexture20, NULL, NULL);
     SDL20_RenderPresent(VideoRenderer20);
-    VideoSurfaceUpdated = SDL_FALSE;
+    VideoSurfaceLastPresentTicks = SDL20_GetTicks();
+    VideoSurfacePresentTicks = 0;
 }
 
 DECLSPEC void SDLCALL
@@ -3148,7 +3151,7 @@ SDL_UpdateRects(SDL12_Surface *surface12, int numrects, SDL12_Rect *rects12)
         if (whole_screen) {  
             PresentScreen();  // flip it now.
         } else {
-            VideoSurfaceUpdated = SDL_TRUE;  // flip it later.
+            VideoSurfacePresentTicks = VideoSurfaceLastPresentTicks + 15;  // flip it later.
         }
     }
 }
@@ -3184,9 +3187,10 @@ DECLSPEC void SDLCALL
 SDL_PumpEvents(void)
 {
     // If the app is doing dirty rectangles, we set a flag and present the
-    //  screen surface when they pump for new events, which we consider a
-    //  sign that they are done rendering for the current frame.
-    if (VideoSurfaceUpdated) {
+    //  screen surface when they pump for new events if we're close to 60Hz,
+    //  which we consider a sign that they are done rendering for the current
+    //  frame and it would make sense to send it to the screen.
+    if (VideoSurfacePresentTicks && SDL_TICKS_PASSED(SDL20_GetTicks(), VideoSurfacePresentTicks)) {
         PresentScreen();
     }
     SDL20_PumpEvents();