Bug in sdl

SDL Development
1

I think I’e found a bug in SDL.
If i switch from fullscreen to windowed mode and runs
SDL_WM_GrabInput(SDL_GRAB_ON) the mouse pointer get stuck in the upper left
corner of the screen. The bug doesn’t appear if I’ve never set fullscreen
before windowed or if I run
SDL_QuitSubSystem(SDL_INIT_VIDEO); SDL_InitSubSystem(SDL_INIT_VIDEO); before
setting the windowed screenmode.
I should probably say that i’ve only tested this under Win98 and WinXP, both
with directx.
Below are some sources to demonstrate the problem.

#include <SDL.h>

int main(int argc, char **argv) {
SDL_Event event;

SDL_Init(SDL_INIT_VIDEO);
SDL_SetVideoMode(640, 480, 32, SDL_SWSURFACE | SDL_FULLSCREEN);

while(1) {
    SDL_WaitEvent(&event);
     if (event.type == SDL_KEYDOWN)
        break;
 }

//SDL_QuitSubSystem(SDL_INIT_VIDEO);
//SDL_InitSubSystem(SDL_INIT_VIDEO);
SDL_SetVideoMode(640, 480, 32, SDL_SWSURFACE);
SDL_WM_GrabInput(SDL_GRAB_ON);

while(1) {
    SDL_WaitEvent(&event);
    if (event.type == SDL_KEYDOWN)
        break;
}

SDL_Quit();
return 0;

}

2

Hi,

yep, I can reproduce the problem on Win98SE. It only seems to
happen using ‘directx’.

I think most people go for the ‘fix’ you are using of quitting
the video subsystem and then re-initialising it.

However, I had a look at the SDL code that does a grab and found this
in ‘wincommon/SDL_syswm.c’:

SDL_GrabMode WIN_GrabInput(_THIS, SDL_GrabMode mode)
{
if ( mode == SDL_GRAB_OFF ) {
ClipCursor(NULL);
…
} else {
ClipCursor(&SDL_bounds);
…
}
}

In your test program, when ClipCursor() is executed, SDL_bounds
is invalid (something like [3,22,3,22]) which has zero width and height.

SDL_bounds is (only) set by the WM_MOVE message in
’wincommon/SDL_sysevents.c’:

case WM_MOVE: {
SDL_VideoDevice *this = current_video;

GetClientRect(SDL_Window, &SDL_bounds);
ClientToScreen(SDL_Window, (LPPOINT)&SDL_bounds);
ClientToScreen(SDL_Window, (LPPOINT)&SDL_bounds+1);
if ( this->input_grab != SDL_GRAB_OFF ) {
ClipCursor(&SDL_bounds);
}
}
break;

and yes, this is producing the invalid rectangle.

Changing WM_MOVE: into WM_WINDOWPOSCHANGED: fixes the problem by
calculating SDL_bounds and executing ClipCursor() when the window
position OR size is changed (and a few other things, but that probably
doesn’t matter),

cheers,
John.> ----- Original Message -----

From: cartwright@linux.nu (Anders A)
To:
Sent: Sunday, June 30, 2002 9:49 AM
Subject: [SDL] bug in sdl

I think I’e found a bug in SDL.
If i switch from fullscreen to windowed mode and runs
SDL_WM_GrabInput(SDL_GRAB_ON) the mouse pointer get stuck in the upper
left
corner of the screen. The bug doesn’t appear if I’ve never set fullscreen
before windowed or if I run
SDL_QuitSubSystem(SDL_INIT_VIDEO); SDL_InitSubSystem(SDL_INIT_VIDEO);
before
setting the windowed screenmode.
I should probably say that i’ve only tested this under Win98 and WinXP,
both
with directx.
Below are some sources to demonstrate the problem.

#include <SDL.h>

int main(int argc, char **argv) {
SDL_Event event;

SDL_Init(SDL_INIT_VIDEO);
SDL_SetVideoMode(640, 480, 32, SDL_SWSURFACE | SDL_FULLSCREEN);

while(1) {
    SDL_WaitEvent(&event);
     if (event.type == SDL_KEYDOWN)
        break;
 }

//SDL_QuitSubSystem(SDL_INIT_VIDEO);
//SDL_InitSubSystem(SDL_INIT_VIDEO);
SDL_SetVideoMode(640, 480, 32, SDL_SWSURFACE);
SDL_WM_GrabInput(SDL_GRAB_ON);

while(1) {
    SDL_WaitEvent(&event);
    if (event.type == SDL_KEYDOWN)
        break;
}

SDL_Quit();
return 0;

}

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