Fake screen resolutions in kkapture

(September 27, 2011)

(Disclaimer: This posting is likely of no interest to people outside of the demoscene :)
The small tool kkapture by ryg of Farbrausch is the only sane way to get a video dump of demos, intros and similar stuff. By grabbing all video and audio output directly from their respective APIs (OpenGL/Direct3D and WinMM/DirectSound) and simulating a fixed time base for the client application, it produces perfect-quality smooth video files suitable for Blu-ray Discs, for example. kkapture doesn’t alter the demos in any other way, though – in particular, the screen setup code from the demos is left untouched, with the result that it’s not possible to kkapture most demos in resolutions higher than the display currently attached to the computer. I did a little modification to kkapture’s code that changes this and allows things like 8-megapixel kkaptures.

But why is high-resolution kkapturing a problem anyway? The first and foremost reason is that modern demos have a resolution selector that lets the user choose from the resolutions supported by the graphics chip and monitor, as reported by Windows’ EnumDisplaySettings API. For obvious reasons, a mode like 1920×1080 is missing from the list if a 1600×1200 display is connected.

But since kkapture is already in the business of hijacking API calls for its audio/video dumping and synchronization functionality anyway, altering the output of EnumDisplaySettings isn’t a big deal either. So that’s what I did: I added code (and a UI) for appending one additional mode to the list returned by that API and voilĂ , that mode appears just nicely in most demos.
However, some additional bases had to be covered to make demos actually run in this mode: First, fullscreen mode isn’t possible, because the demo would then request a display mode the display driver doesn’t know of. For OpenGL demos, I circumvent this by neutering the ChangeDisplaySettings API call, which means that the demo runs in a borderless window instead of fullscreen. In Direct3D, things are a bit different though. Since I don’t know enough about that API, I did not implement a similar hack, meaning that Direct3D fullscreen mode does not work with custom resolutions, period. But that’s usually not a big deal, because most demos offer an option to run in windowed mode anyway. The modified kkapture version also makes sure that the demo can actually create a window that is larger than the screen. (Normally, Windows limits the client area of application windows to the screen size; this is worked around by intercepting DefWindowProc and making sure that WM_GETMINMAXINFO returns sufficiently high values for ptMaxTrackSize.)


Here’s a modified version of kkapture:

kkapture_mod.zip (185k) (obsolete, see update below)

It has a new option to fake an additional screen resolution. When using it, make sure that you run the demo in windowed mode, otherwise weirdness may ensue.

Included in the archive is a .diff file showing the changes relative to the current (as of 2011-09-27) Git version of kkapture. In addition to the fake video mode changes, it contains two minor fixes to make kkapture compile on Visual C++ Express 2010, but these shouldn’t break stuff for other VS versions either.

Update [2012-08-21]: The feature discussed in this article has now been integrated into the upstream version of kkapture, so please get a current binary (or sources) directly from the official kkapture page.

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