Animation using pure C/Win32

[DelphiCoder]

As part of familiarizing myself with the Win32 API, I wrote a simple animation program in C. The program has a struct for each bitmap, holding information such as its location, visibility, mask (for transparency), etc. Then I have a separate thread running that has a WHILE loop that looks like this:

WHILE (TRUE)
{
   /* update all structs (bitmap locations, etc) */
   SleepEx(iSpeed, FALSE);
   InvalidateRect(hwnd, lpRect, TRUE);  
}
 

In my WM_PAINT case in the window procedure, I'm simply drawing all my bitmaps based on their updated attributes.

The animation on my home computer seemed smooth and reasonable (it looked good), but then I copied the EXE to my work computer, and when I tried it at work, it seems to run in slow motion. It's still smooth, not skipping 'frames' and not showing any graphical problems, but it runs in slow motion. I do notice that every now and then the animation speeds up to its normal pace for a few seconds, but then it slows down again.

I know the problem is not with my work computer. I've run simple games on it before and their animation speeds are normal.

Any advice?

[Savage]

@DelphiCoder
Probably has to do something with iSpeed, how do you calculate it?

[DelphiCoder]

I discovered the problem was with SleepEx(). I ran a diagnostics program that I wrote. It takes 157 ms to execute a loop containing 100 ms worth of SleepEx() calls on my work computer. On my home computer, it's exactly 100 ms.

[JosAH]

@DelphiCoder
Timers aren't very accurate on a Microsoft Windows PC. It is not a real time operating system by far.

kind regards,

Jos

[DelphiCoder]

@Savage
I don't. It's a constant.

[DelphiCoder]

@JosAH
So how do they make games that run on Windows?

[Savage]

@DelphiCoder
They don't use WM_PAINT event, in fact whole message loop has to be improved.

Read http://www.mvps.org/directx/articles..._game_loop.htm

[DelphiCoder]

@Savage

Thanks so much! This is a great article. I will rewrite my app accordingly.

[Banfa]

@DelphiCoder
Also you don't use Sleep (or SleepEx) which only has ms resolution if that (DOS and therefore Windows 2.xxx and 3 and 95 had a maximum timer resolution of 50ms IIRC).

Use wait-able timers which are OS objects with much better resolution and accuracy.