dix: force a minimum of 0 for screen coordinates.

Currently the root coordinates may fall into ]-1..0] if the subpixel
remainder is less than 0. Screen coordinates mustn't go below 0, so use
miPointerSetPosition to cap off the remainder if the coordinates are below
0.

This is cheating a bit, a more comprehensive solution to deal with subpixels
correctly when crossing screens is needed. For now, this'll do.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Acked-by: Simon Thum <simon.thum@gmx.de>

1 files changed, 13 insertions, 0 deletions

diff --git a/dix/getevents.c b/dix/getevents.c
index 5224d31eb..2df32e8f5 100644
--- a/dix/getevents.c
+++ b/dix/getevents.c
@@ -783,2 +783,15 @@ positionSprite(DeviceIntPtr dev, int *x, int *y, float x_frac, float y_frac,
 
+    /* Hit the left screen edge? */
+    if (*screenx <= 0 && *screenx_frac < 0.0f)
+    {
+        *screenx_frac = 0.0f;
+        x_frac = 0.0f;
+    }
+    if (*screeny <= 0 && *screeny_frac < 0.0f)
+    {
+        *screeny_frac = 0.0f;
+        y_frac = 0.0f;
+    }
+
+
     old_screenx = *screenx;