st/dri: update dri2 drawables when viewport is changed

Fixes gnome-shell on nouveau, as well as window resize with various
other applications.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

src/gallium/include/pipe/p_screen.h

@@ -266,6 +266,11 @@ struct pipe_screen {
 
    void (*video_surface_destroy)( struct pipe_video_surface *vsfc );
 
+   /**
+    * Do any special operations to ensure buffer size is correct
+    */
+   void (*update_buffer)( struct pipe_screen *ws,
+                          void *context_private );
 
    /**
     * Do any special operations to ensure frontbuffer contents are

src/gallium/state_trackers/dri/dri_drawable.c

@@ -267,6 +267,14 @@ void dri2_set_tex_buffer(__DRIcontext *pDRICtx, GLint target,
    dri2_set_tex_buffer2(pDRICtx, target, GLX_TEXTURE_FORMAT_RGBA_EXT, dPriv);
 }
 
+void
+dri_update_buffer(struct pipe_screen *screen, void *context_private)
+{
+   struct dri_context *ctx = (struct dri_context *)context_private;
+
+   dri_get_buffers(ctx->dPriv);
+}
+
 void
 dri_flush_frontbuffer(struct pipe_screen *screen,
 		      struct pipe_surface *surf, void *context_private)

src/gallium/state_trackers/dri/dri_drawable.h

@@ -80,6 +80,9 @@ dri_create_buffer(__DRIscreen * sPriv,
 		  __DRIdrawable * dPriv,
 		  const __GLcontextModes * visual, boolean isPixmap);
 
+void
+dri_update_buffer(struct pipe_screen *screen, void *context_private);
+
 void
 dri_flush_frontbuffer(struct pipe_screen *screen,
 		      struct pipe_surface *surf, void *context_private);

src/gallium/state_trackers/dri/dri_screen.c

@@ -308,6 +308,7 @@ dri_init_screen2(__DRIscreen * sPriv)
    }
 
    /* We need to hook in here */
+   screen->pipe_screen->update_buffer = dri_update_buffer;
    screen->pipe_screen->flush_frontbuffer = dri_flush_frontbuffer;
 
    driParseOptionInfo(&screen->optionCache,

src/mesa/state_tracker/st_cb_viewport.c

@@ -42,8 +42,8 @@ static void st_viewport(GLcontext * ctx, GLint x, GLint y,
 {
    struct st_context *st = ctx->st;
 
-   if (st->pipe->winsys && st->pipe->winsys->update_buffer)
-      st->pipe->winsys->update_buffer( st->pipe->winsys,
+   if (st->pipe->screen && st->pipe->screen->update_buffer)
+      st->pipe->screen->update_buffer( st->pipe->screen,
                                        st->pipe->priv );
 }