from SDL to Qt: the underwater effect

Doing a real underwater after effect would involve creating a believable water caustics plus some vertex shader incantations, both are far away from my expertise and it would even have taken more than an hour I would like to spend on the rainy Sunday morning preparing an example for this week's Graphics Dojo corner. Instead, I just cheated and ported my previous SDL version of Quake-like underwater effect to use QImage, and that became the example. Since this is an animation effect, the still photo below could not really depict the idea. So, just grab the code, build it, drag-and-drop your favorite photo and stare at the result for few seconds.