diff options
authorKeith Packard <>2010-08-20 10:01:48 -0700
committerJulien Cristau <>2010-08-21 20:41:37 +0100
commit7c544986656713b5bbdb936bb7c3cb5a83d9f833 (patch)
parentf43e105ee8741c8be49a602b08752f2390f094f7 (diff)
fb: make isClipped always reject negative coordinates (bug 11503)
A window with either dimension > 32767 can be positioned such that coordinates > 32767 are visible on the screen. Attempts to draw to those pixels will generate coordinates wrapped around to negative values. The optimized clipping macro, 'isClipped', in fbbits.h, computes clipping in window space rather than screen space using int16 values, and so it too has coordinates wrapped around to negative values and hence ends up accepting the wrapped drawing coordinates. Two possible fixes for this problem 1) Detect wrapped region coordinates and clip those to 32767. 2) Detect negative incoming coordinates and reject those This patch takes the second approach as it is much shorter, simply detecting when either X or Y incoming coordinate is negative, which can never be 'within' any drawable. Signed-off-by: Keith Packard <> Reviewed-by: Adam Jackson <> (cherry picked from commit 3e56efcfb63677cd8574e1e435e61d96f79ea536)
1 files changed, 1 insertions, 1 deletions
diff --git a/fb/fbbits.h b/fb/fbbits.h
index 44991f106..b8af78571 100644
--- a/fb/fbbits.h
+++ b/fb/fbbits.h
@@ -25,7 +25,7 @@
* underlying datatypes instead of masks
-#define isClipped(c,ul,lr) ((((c) - (ul)) | ((lr) - (c))) & 0x80008000)
+#define isClipped(c,ul,lr) (((c) | ((c) - (ul)) | ((lr) - (c))) & 0x80008000)
#include <dix-config.h>