Removed manual calling of glFlush and made glFinish optional

Actually neither glFlush nor glFinish need to be called manually [1].
However, the rendering pipeline is then free to queue up future frames
which can cause a lag which is especially noticable with mouse movement.

To avoid this lag, we call glFinish after SDL_GL_SwapBuffers. This makes
sure processing of the next frame does not start before the current
frame is being displayed.

[1] http://www.opengl.org/wiki/Common_Mistakes#glFinish_and_glFlush

Reviewed-by: Yohann Ferreira
Sounded-fine-to: Erik Schilling

1 files changed, 11 insertions, 0 deletions

diff --git a/src/openglgraphics.h b/src/openglgraphics.h
index a1d78e46..63c32261 100644
--- a/src/openglgraphics.h
+++ b/src/openglgraphics.h
@@ -43,6 +43,16 @@ class OpenGLGraphics : public Graphics
         void setSync(bool sync);
         bool getSync() const { return mSync; }
 
+        /**
+         * Sets whether input lag should be reduced.
+         *
+         * This means waiting until the graphics card has finished drawing and
+         * displaying the current frame until continuing towards the next,
+         * possibly at the cost of performance and CPU usage.
+         */
+        void setReduceInputLag(bool reduceInputLag);
+        bool getReduceInputLag() const { return mReduceInputLag; }
+
         bool setVideoMode(int w, int h, int bpp, bool fs, bool hwaccel);
 
         bool drawImage(Image *image,
@@ -114,6 +124,7 @@ class OpenGLGraphics : public Graphics
         bool mAlpha, mTexture;
         bool mColorAlpha;
         bool mSync;
+        bool mReduceInputLag;
 };
 #endif //USE_OPENGL