Commit b9567776d7ce15b2b5bb7b6eb0e124353fe42b44
2013-09-27T23:35:17
# User Darren Salt <devspam@moreofthesa.me.uk> # Date 1379621782 -3600 # Thu Sep 19 21:16:22 2013 +0100 Work around a false-positive in the X11 mouse wheel code This false positive occurs when one particular button on my mouse is pressed. The kernel which I'm using is patched to cause a release event to be synthesised immediately when the mouse says that this button is pressed because the mouse doesn't signal release until the button is next pressed. (Also documents a false negative, observed with the horizontal scroll wheel on the same mouse.)
diff --git a/src/video/x11/SDL_x11events.c b/src/video/x11/SDL_x11events.c
index 0b577ec..c260019 100644
--- a/src/video/x11/SDL_x11events.c
+++ b/src/video/x11/SDL_x11events.c
@@ -135,7 +135,9 @@ static Bool X11_IsWheelCheckIfEvent(Display *display, XEvent *chkev,
XPointer arg)
{
XEvent *event = (XEvent *) arg;
+ /* we only handle buttons 4 and 5 - false positive avoidance */
if (chkev->type == ButtonRelease &&
+ (event->xbutton.button == Button4 || event->xbutton.button == Button5) &&
chkev->xbutton.button == event->xbutton.button &&
chkev->xbutton.time == event->xbutton.time)
return True;
@@ -150,7 +152,12 @@ static SDL_bool X11_IsWheelEvent(Display * display,XEvent * event,int * ticks)
however, mouse wheel events trigger a button press and a button release
immediately. thus, checking if the same button was released at the same
time as it was pressed, should be an adequate hack to derive a mouse
- wheel event. */
+ wheel event.
+ However, there is broken and unusual hardware out there...
+ - False positive: a button for which a release event is
+ generated (or synthesised) immediately.
+ - False negative: a wheel which, when rolled, doesn't have
+ a release event generated immediately. */
if (XCheckIfEvent(display, &relevent, X11_IsWheelCheckIfEvent,
(XPointer) event)) {