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Fixed bug 3015 - grab mouse inconsistent state
Martin Gerhardy

Not sure - but I think there might be a logic flaw in SDL_SetWindowGrab.

The problem here is that this modifies the window flags and e.g. sets
SDL_WINDOW_INPUT_GRABBED - but the _this->grabbed_window pointer is not
yet set.

Then in SDL_UpdateWindowGrab the _this->grabbed_window pointer is only
set if the function pointer _this->SetWindowGrab is not NULL. But if
this is NULL, the _this->grabbed_window pointer is never set, but every
future call to any of the grab functions include an assert for:
SDL_assert(!_this->grabbed_window || ((_this->grabbed_window->flags &
SDL_WINDOW_INPUT_GRABBED) != 0));

That means the first call works, the second always fails and triggers
the assert.
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slouken committed Jun 16, 2015
1 parent ccc12a3 commit 59d34bc35dbe9d23e78f137c08e47fecddcc93a4
Showing with 19 additions and 17 deletions.
  1. +19 −17 src/video/SDL_video.c
@@ -2122,28 +2122,30 @@ SDL_GetWindowGammaRamp(SDL_Window * window, Uint16 * red,
void
SDL_UpdateWindowGrab(SDL_Window * window)
{
if (_this->SetWindowGrab) {
SDL_Window *grabbed_window;
SDL_bool grabbed;
if ((SDL_GetMouse()->relative_mode || (window->flags & SDL_WINDOW_INPUT_GRABBED)) &&
(window->flags & SDL_WINDOW_INPUT_FOCUS)) {
grabbed = SDL_TRUE;
} else {
grabbed = SDL_FALSE;
}
SDL_Window *grabbed_window;
SDL_bool grabbed;
if ((SDL_GetMouse()->relative_mode || (window->flags & SDL_WINDOW_INPUT_GRABBED)) &&
(window->flags & SDL_WINDOW_INPUT_FOCUS)) {
grabbed = SDL_TRUE;
} else {
grabbed = SDL_FALSE;
}

grabbed_window = _this->grabbed_window;
if (grabbed) {
if (grabbed_window && (grabbed_window != window)) {
/* stealing a grab from another window! */
grabbed_window->flags &= ~SDL_WINDOW_INPUT_GRABBED;
grabbed_window = _this->grabbed_window;
if (grabbed) {
if (grabbed_window && (grabbed_window != window)) {
/* stealing a grab from another window! */
grabbed_window->flags &= ~SDL_WINDOW_INPUT_GRABBED;
if (_this->SetWindowGrab) {
_this->SetWindowGrab(_this, grabbed_window, SDL_FALSE);
}
_this->grabbed_window = window;
} else if (grabbed_window == window) {
_this->grabbed_window = NULL; /* ungrabbing. */
}
_this->grabbed_window = window;
} else if (grabbed_window == window) {
_this->grabbed_window = NULL; /* ungrabbing. */
}

if (_this->SetWindowGrab) {
_this->SetWindowGrab(_this, window, grabbed);
}
}

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