kewlpc posted:

He's talking about 2D sidescrolling terrain with destruction, a la Worms, not 3D terrain.

The question was how to do pixel-perfect terrain destruction like in Worms, where a bomb "eats" the terrain, then the terrain collapses. That was answered already.

But I think now he's wondering how to actually draw it. Tiling alone isn't enough, since you'd need a tile for each possible way each piece of terrain could be destroyed, which would require a huge amount of video memory, defeating the whole point of tiling in the first place.

Honestly, the easiest way is to forgo using the 3D hardware and just do it all via software blitting. Then you can store your whole level as one big image in memory and destroy it as you go. But then you don't get to have pretty explosions, free alpha blending, etc.

What I'd do is decide if having the terrain collapse after the bomb eats away at it is necessary. If not, you can still use the 3D hardware as a fast 2D blitter:

1)When an explosion occurs, eat away the terrain in the destruction bitmap. Use the destruction bitmap for collision detection.

2)Save the center point and radius of the explosion in a list.

3)Draw your background

4)Draw explosions (even ones that have already happened) into the stencil buffer. Just draw a circle, using the center point and radius from your list.

5)Draw the terrain using tiling, but with the stencil buffer check turned on. Wherever an explosion has taken place, the terrain won't get drawn.

You should probably prune the explosion list periodically, looking for things like one explosion that completely overlaps another, to reduce overdraw in the stencil buffer.