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Bug 2405

Summary: SDL_SetRelativeMouseMode is slow
Product: SDL Reporter: Guillaume Payet <payetguillaume2008>
Component: eventsAssignee: Sam Lantinga <slouken>
Status: RESOLVED INVALID QA Contact: Sam Lantinga <slouken>
Severity: normal    
Priority: P2 CC: gabomdq
Version: 2.0.1   
Hardware: x86_64   
OS: Windows 8   

Description Guillaume Payet 2014-02-19 00:45:26 UTC 
When I set SDL_SetRelativeMouseMode(SDL_TRUE), The events lag behind (as if the event queue was not processed fast enought or the events take time to be generated).
I removed all kinds of processing in my main loop to test the performance but it still lags.
Also, if I use SDL_PollEvent (instead of SDL_WaitEvent), I keep receiving relative mouse motion events of 1px when I stop moving the mouse (the events sort of "drift").
Comment 1 Gabriel Jacobo 2014-02-19 13:58:29 UTC 
Can you show us what your main loop looks like?
Comment 2 Guillaume Payet 2014-02-19 20:33:22 UTC 
If I comment out all drawings and processing, the minimal loop where I can still experience lag is:

do
{
    SDL_PollEvent(event);

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glFlush();

    SDL_GL_SwapWindow(SDL_GL_GetCurrentWindow());
}
while (event->type == SDL_KEYDOWN && event->key.keysym.sym == SDLK_ESCAPE);
Comment 3 Gabriel Jacobo 2014-02-19 20:37:37 UTC 
You should poll all events until the queue is empty, then run your render code (specially SDL_GL_SwapWindow, since it can get "stuck" waiting for the vertical retrace).
If after making this change you still get laggy behavior, feel free to reopen.
Comment 4 Guillaume Payet 2014-02-19 20:43:35 UTC 
It works. Thanks