xmesa: set back-buffer's drawable field

Fixes back-buffer rendering when MESA_BACK_BUFFER=pixmap

diff --git a/src/mesa/drivers/x11/xm_buffer.c b/src/mesa/drivers/x11/xm_buffer.c
index 7ad67bc34dae15b7001aec578ebda0243b06ada4..821e2a8e082e42198d0655836f2e080192865708 100644 (file)
--- a/src/mesa/drivers/x11/xm_buffer.c
+++ b/src/mesa/drivers/x11/xm_buffer.c
@@ -229,6 +229,7 @@ alloc_back_buffer(XMesaBuffer b, GLuint width, GLuint height)
       }
 
       b->backxrb->ximage = NULL;
+      b->backxrb->drawable = b->backxrb->pixmap;
    }
 }