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X11: Simplified mousewheel event handling.

Under load, this would race and report an incorrect mouse button event instead
of a wheel event.

Fixes Bugzilla #2987.
  • Loading branch information
icculus committed Aug 13, 2015
1 parent da6f222 commit 874bf8650437ab7561b0a845d910abd947383160
Showing with 20 additions and 50 deletions.
  1. +20 −50 src/video/x11/SDL_x11events.c
@@ -167,54 +167,20 @@ static SDL_bool X11_KeyRepeat(Display *display, XEvent *event)
return d.found;
}

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 ||
event->xbutton.button == 6 || event->xbutton.button == 7) &&
chkev->xbutton.button == event->xbutton.button &&
chkev->xbutton.time == event->xbutton.time)
return True;
return False;
}

static SDL_bool X11_IsWheelEvent(Display * display,XEvent * event,int * xticks,int * yticks)
static SDL_bool
X11_IsWheelEvent(Display * display,XEvent * event,int * xticks,int * yticks)
{
XEvent relevent;
if (X11_XPending(display)) {
/* according to the xlib docs, no specific mouse wheel events exist.
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.
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 (X11_XCheckIfEvent(display, &relevent, X11_IsWheelCheckIfEvent,
(XPointer) event)) {

/* by default, X11 only knows 5 buttons. on most 3 button + wheel mouse,
Button4 maps to (vertical) wheel up, Button5 maps to wheel down.
Horizontal scrolling usually maps to 6 and 7 which have no name */
if (event->xbutton.button == Button4) {
*yticks = 1;
}
else if (event->xbutton.button == Button5) {
*yticks = -1;
}
else if (event->xbutton.button == 6) {
*xticks = 1;
}
else if (event->xbutton.button == 7) {
*xticks = -1;
}
return SDL_TRUE;
}
/* according to the xlib docs, no specific mouse wheel events exist.
However, the defacto standard is that the vertical wheel is X buttons
4 (up) and 5 (down) and a horizontal wheel is 6 (left) and 7 (right). */

/* Xlib defines "Button1" through 5, so we just use literals here. */
switch (event->xbutton.button) {
case 4: *yticks = 1; return SDL_TRUE;
case 5: *yticks = -1; return SDL_TRUE;
case 6: *xticks = 1; return SDL_TRUE;
case 7: *xticks = -1; return SDL_TRUE;
default: break;
}
return SDL_FALSE;
}
@@ -1056,9 +1022,13 @@ X11_DispatchEvent(_THIS)

case ButtonRelease:{
int button = xevent.xbutton.button;
if (button > 7) {
/* see explanation at case ButtonPress */
button -= (8-SDL_BUTTON_X1);
/* The X server sends a Release event for each Press for wheels. Ignore them. */
int xticks = 0, yticks = 0;
if (!X11_IsWheelEvent(display,&xevent,&xticks, &yticks)) {
if (button > 7) {
/* see explanation at case ButtonPress */
button -= (8-SDL_BUTTON_X1);
}
}
SDL_SendMouseButton(data->window, 0, SDL_RELEASED, button);
}

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