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Whenever I lose focus from my game window, I go from ~60FPS to 6000+, then when the window gains focus again, I go back to around 60 frames per second. And yes, this happens every time I run my game, including Release mode.

Here is an example log output from my game:

[INFO] [10/01/2013 22:37:42.355] Window Gained Focus!
[INFO] [10/01/2013 22:37:45.365] Frames Per Second: 60.0439
[INFO] [10/01/2013 22:37:45.365] Frame Counter: 60
[INFO] [10/01/2013 22:37:46.365] Frames Per Second: 60.0324
[INFO] [10/01/2013 22:37:46.365] Frame Counter: 60
[INFO] [10/01/2013 22:37:47.381] Frames Per Second: 59.4341
[INFO] [10/01/2013 22:37:47.382] Frame Counter: 58
[INFO] [10/01/2013 22:37:49.669] Window Lost Focus!
[INFO] [10/01/2013 22:37:50.383] Frames Per Second: 1240.02
[INFO] [10/01/2013 22:37:50.383] Frame Counter: 9561
[INFO] [10/01/2013 22:37:51.384] Frames Per Second: 1839.02
[INFO] [10/01/2013 22:37:51.384] Frame Counter: 6662
[INFO] [10/01/2013 22:37:52.77] Window Gained Focus!
[INFO] [10/01/2013 22:37:52.400] Frames Per Second: 1656.77
[INFO] [10/01/2013 22:37:52.400] Frame Counter: 34
[INFO] [10/01/2013 22:37:53.400] Frames Per Second: 1512.46
[INFO] [10/01/2013 22:37:53.400] Frame Counter: 60
[INFO] [10/01/2013 22:37:54.401] Frames Per Second: 1391.89
[INFO] [10/01/2013 22:37:54.402] Frame Counter: 60
[INFO] [10/01/2013 22:37:55.402] Frames Per Second: 1289.78
[INFO] [10/01/2013 22:37:55.402] Frame Counter: 58
[INFO] [10/01/2013 22:37:55.876] Quitting with error code: 0

The frame counter is just a simple integer that I increment every loop in the game, and then reset (and print it out) every second. Here is the implementation of my game loop, (inside the run() function), based off of this article.

Is this a problem with my loop, or is this a problem with SDL? I'm not sure why my frame rate is rocketing up.

share|improve this question
Is your update function paired with the render function? Does it get called less if you focus away? – Vaughan Hilts Jan 10 '13 at 12:26
@VaughanHilts My update function gets called ~100 times per frame, regardless of the game's FPS (and regardless of losing focus). However, my drawing is done per-frame, therefore it is getting called 6000+ (when I lose focus) times per second. (I don't actually have any rendering code being called though) – miguel.martin Jan 10 '13 at 12:30
The loop here is fairly irrelevant - all the real work, including any SDL specific stuff, is being done in functions we can't see. – Kylotan Jan 10 '13 at 13:07
up vote 6 down vote accepted

60 fps in focus mode is very suspicious, it must be vsync.

Why vsync is turned off when the app loses focus is not a question I can answer though.

share|improve this answer
Sure seems like it, I stop flipping opengl's buffer in my render function and the FPS was at 13000+ even when focused. – miguel.martin Jan 10 '13 at 13:31

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