Following on from yesterday's fixed point maths routines, here's a little demo which builds on that. It's another oldie, again from around 2002/3, which I've used in a more advanced form on quite a few projects. It's a very simple texture mapper, visually in the style of the SNES's famed mode 7. Given a 2D map, it presents the image as a horizontal texture mapped surface. It's primitive stuff but can be used to quite nice effect, and with it being entirely software based it doesn't require any additional APIs on the phone.
Grab the source and take a look at Renderer.java. Most of the work is done in renderFloor(), which simply works out a pixel offset for each scanline and fills the buffer accordingly. I've taken out some of the optimisations so it's easier to read, but even still it's no slouch!