http://denvish.net/u..40901254_terrain.php
Click to asplode, shift-click to grow
Arrow keys to move, spacebar to jump (sorry forgot to switch jump to the up button)
How it works is that the map is a bitmap data. When you click it makes a black circle appear and grow. The black circle is made visible, drawn to the bitmap data, then made invisible each frame. All the black pixels on the bitmap data are made invisible with color threshold.
Building stuff works in a similar way, except there are now black pixels. Quality has to be low, or else the anti-alias edges do get removed.
This is just a demo engine