winemac: Force swap interval to 0 for single-buffered contexts to avoid vsync'ed flushes.

dlls/winemac.drv/opengl.c

@@ -2901,7 +2901,9 @@ static BOOL macdrv_wglSwapIntervalEXT(int interval)
         return FALSE;
     }
 
-    if (interval > 1)
+    if (!pixel_formats[context->format - 1].double_buffer)
+        interval = 0;
+    else if (interval > 1)
         interval = 1;
 
     value = interval;
@@ -3238,8 +3240,14 @@ static BOOL create_context(struct wgl_context *context, CGLContextObj share)
     }
 
     /* According to the WGL_EXT_swap_control docs, the default swap interval for
-       a context is 1.  CGL contexts default to 0, so we need to set it. */
-    swap_interval = 1;
+       a context is 1.  CGL contexts default to 0, so we need to set it.  This
+       only make sense for double-buffered contexts, though.  In theory, for
+       single-buffered contexts, there's no such thing as a swap.  But OS X
+       will synchronize flushes of single-buffered contexts if this is set. */
+    if (pf->double_buffer)
+        swap_interval = 1;
+    else
+        swap_interval = 0;
     err = CGLSetParameter(context->cglcontext, kCGLCPSwapInterval, (GLint*)&swap_interval);
     if (err != kCGLNoError)
         WARN("CGLSetParameter(kCGLCPSwapInterval) failed with error %d %s; leaving un-vsynced\n", err, CGLErrorString(err));