From 28c6fa192ace58f705f1b88d32a2a8a7587875a7 Mon Sep 17 00:00:00 2001
From: Sam Lantinga <slouken@libsdl.org>
Date: Mon, 11 Feb 2013 17:02:13 -0800
Subject: [PATCH]        Workaround for NVIDIA bug in glXSwapIntervalEXT.

       This works around a bug in NVIDIA's implementation of
       glXSwapIntervalEXT, where it ignores updates to what it *thinks* is the
       current value, even though glXQueryDrawable returns a different value.

       Bug reported to NVIDIA and will hopefully be a part of 319.xx.

       Also a fix for invalidly treating glXSwapIntervalEXT as having an int
       return value (it's void).
---
 build-scripts/ltmain.sh       |  0
 src/video/x11/SDL_x11opengl.c | 24 +++++++++++++++++-------
 src/video/x11/SDL_x11opengl.h |  2 +-
 3 files changed, 18 insertions(+), 8 deletions(-)
 mode change 100644 => 100755 build-scripts/ltmain.sh

diff --git a/build-scripts/ltmain.sh b/build-scripts/ltmain.sh
old mode 100644
new mode 100755
diff --git a/src/video/x11/SDL_x11opengl.c b/src/video/x11/SDL_x11opengl.c
index 9e80d0cbf..f9d4b5005 100644
--- a/src/video/x11/SDL_x11opengl.c
+++ b/src/video/x11/SDL_x11opengl.c
@@ -332,7 +332,7 @@ X11_GL_InitExtensions(_THIS)
     _this->gl_data->HAS_GLX_EXT_swap_control_tear = SDL_FALSE;
     if (HasExtension("GLX_EXT_swap_control", extensions)) {
         _this->gl_data->glXSwapIntervalEXT =
-            (int (*)(Display*,GLXDrawable,int))
+            (void (*)(Display*,GLXDrawable,int))
                 X11_GL_GetProcAddress(_this, "glXSwapIntervalEXT");
         if (HasExtension("GLX_EXT_swap_control_tear", extensions)) {
             _this->gl_data->HAS_GLX_EXT_swap_control_tear = SDL_TRUE;
@@ -667,13 +667,23 @@ X11_GL_SetSwapInterval(_THIS, int interval)
         Display *display = ((SDL_VideoData *) _this->driverdata)->display;
         const SDL_WindowData *windowdata = (SDL_WindowData *)
             _this->current_glwin->driverdata;
+
         Window drawable = windowdata->xwindow;
-        status = _this->gl_data->glXSwapIntervalEXT(display,drawable,interval);
-        if (status != 0) {
-            SDL_SetError("glxSwapIntervalEXT failed");
-        } else {
-            swapinterval = interval;
-        }
+
+        /*
+         * This is a workaround for a bug in NVIDIA drivers. Bug has been reported
+         * and will be fixed in a future release (probably 319.xx).
+         *
+         * There's a bug where glXSetSwapIntervalEXT ignores updates because
+         * it has the wrong value cached. To work around it, we just run a no-op
+         * update to the current value.
+         */
+        int currentInterval = _this, X11_GL_GetSwapInterval(_this);
+        _this->gl_data->glXSwapIntervalEXT(display, drawable, currentInterval);
+        _this->gl_data->glXSwapIntervalEXT(display, drawable, interval);
+
+        status = 0;
+        swapinterval = interval;
     } else if (_this->gl_data->glXSwapIntervalMESA) {
         status = _this->gl_data->glXSwapIntervalMESA(interval);
         if (status != 0) {
diff --git a/src/video/x11/SDL_x11opengl.h b/src/video/x11/SDL_x11opengl.h
index a786b773e..2b4780208 100644
--- a/src/video/x11/SDL_x11opengl.h
+++ b/src/video/x11/SDL_x11opengl.h
@@ -40,7 +40,7 @@ struct SDL_GLDriverData
     Bool(*glXMakeCurrent) (Display*,GLXDrawable,GLXContext);
     void (*glXSwapBuffers) (Display*, GLXDrawable);
     void (*glXQueryDrawable) (Display*,GLXDrawable,int,unsigned int*);
-    int (*glXSwapIntervalEXT) (Display*,GLXDrawable,int);
+    void (*glXSwapIntervalEXT) (Display*,GLXDrawable,int);
     int (*glXSwapIntervalSGI) (int);
     int (*glXSwapIntervalMESA) (int);
     int (*glXGetSwapIntervalMESA) (void);