master 76d79e1576: Prevent some NoExpose events from being generated

[Po Lu]

branch: master
commit 76d79e1576956eb0c07eb830fd75f7b7c4192efe
Author: Po Lu <luangruo@yahoo.com>
Commit: Po Lu <luangruo@yahoo.com>

    Prevent some NoExpose events from being generated
    
    * src/xterm.c (x_scroll_run): Use the rendering extension if
    available to avoid NoExpose events.
---
 src/xterm.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/src/xterm.c b/src/xterm.c
index 948afa5680..89ec43b470 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -6037,12 +6037,24 @@ x_scroll_run (struct window *w, struct run *run)
     }
   else
 #endif /* USE_CAIRO */
-    XCopyArea (FRAME_X_DISPLAY (f),
-              FRAME_X_DRAWABLE (f), FRAME_X_DRAWABLE (f),
-              f->output_data.x->normal_gc,
-              x, from_y,
-              width, height,
-              x, to_y);
+    {
+#ifdef HAVE_XRENDER
+      /* Avoid useless NoExpose events.  This way, we only get regular
+        exposure events when there is actually something to
+        expose.  */
+      if (FRAME_X_PICTURE (f) != None)
+       XRenderComposite (FRAME_X_DISPLAY (f), PictOpSrc, FRAME_X_PICTURE (f),
+                         None, FRAME_X_PICTURE (f), x, from_y, 0, 0, x, to_y,
+                         width, height);
+      else
+#endif
+       XCopyArea (FRAME_X_DISPLAY (f),
+                  FRAME_X_DRAWABLE (f), FRAME_X_DRAWABLE (f),
+                  f->output_data.x->normal_gc,
+                  x, from_y,
+                  width, height,
+                  x, to_y);
+    }
 
   unblock_input ();
 }