st/xlib: Notify the context when the front/back buffers are swapped.

The current context should be notified when the the front/back buffers
of the current drawable are swapped.  The notification was skipped when
xmesa_strict_invalidate is false (the default).

This fixes fdo bug #29774.

src/gallium/state_trackers/glx/xlib/xm_api.c

@@ -1086,20 +1086,30 @@ XMesaDestroyBuffer(XMesaBuffer b)
 }
 
 
+/**
+ * Notify the binding context to validate the buffer.
+ */
+void
+xmesa_notify_invalid_buffer(XMesaBuffer b)
+{
+   XMesaContext xmctx = XMesaGetCurrentContext();
+
+   if (xmctx && xmctx->xm_buffer == b)
+      xmctx->st->notify_invalid_framebuffer(xmctx->st, b->stfb);
+}
+
+
 /**
  * Query the current drawable size and notify the binding context.
  */
 void
 xmesa_check_buffer_size(XMesaBuffer b)
 {
-   XMesaContext xmctx = XMesaGetCurrentContext();
-
    if (b->type == PBUFFER)
       return;
 
    xmesa_get_window_size(b->xm_visual->display, b, &b->width, &b->height);
-   if (xmctx && xmctx->xm_buffer == b)
-      xmctx->st->notify_invalid_framebuffer(xmctx->st, b->stfb);
+   xmesa_notify_invalid_buffer(b);
 }
 
 

src/gallium/state_trackers/glx/xlib/xm_api.h

@@ -360,6 +360,9 @@ extern void
 xmesa_get_window_size(Display *dpy, XMesaBuffer b,
                       GLuint *width, GLuint *height);
 
+extern void
+xmesa_notify_invalid_buffer(XMesaBuffer b);
+
 extern void
 xmesa_check_buffer_size(XMesaBuffer b);
 

src/gallium/state_trackers/glx/xlib/xm_st.c

@@ -339,6 +339,10 @@ xmesa_swap_st_framebuffer(struct st_framebuffer_iface *stfbi)
          tmp = *front;
          *front = *back;
          *back = tmp;
+
+         /* the current context should validate the buffer after swapping */
+         if (!xmesa_strict_invalidate)
+            xmesa_notify_invalid_buffer(xstfb->buffer);
       }
 
       if (xmesa_strict_invalidate)