I'm looking at making a game that works very differently to the ones I've made previously. Usually I just make tile-based games, but I want to experiment a bit more.

The game I want to make will have a terrain similar to what you've seen in the "worms" games (curved, weirdly shaped hilly type land) which would be predrawn and loaded as an image. I want to have the "bullets" bounce correctly when hitting the terrain.

From my searching it appears the best solution for the collision detection is to use a per-pixel approach. I've looked up some tutorials on it and will have to experiment (if anyone has some suggestions for tutorials on this I would be grateful).

What I'm not sure how to find though is what to use for calculating what angle the 'bullet' should bounce off in when it hits the terrain - or more specifically how to determine what angle the terrain is that it's hitting. I think that what I need to do is grab a square of pixels and somehow calculate what angle they are forming so I can calculate the continued trajectory.

Would this be the correct method or is there a better way to do this?

If I remember correctly, worms had strange bouncing and things didn't always reflect as you'd expect them to. It was probably done on a pixel basis. If the missile hits the corner of a pixel, the normal is at that 45 degree angle. If the missile hits the side of a pixel, the normal is at that 90 degree angle.

The way I would do it is to create a search radius ... maybe a square of 8x8 pixels, and calculate it's centre of mass (earth pixel = 0, air pixel = 1). Then calculate the vector from the centre of the square to the centre of mass, and normalise it.

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Thank you for your advice. Sounds perfect. I have a lot of reading up and testing to do now