Home » Implementing a 2D destructible landscape (like Worms)

Implementing a 2D destructible landscape (like Worms)

Solutons:


I don’t know how the landscape in worms was implemented exactly, but I’m pretty sure they used a bitmap for the landscape (at least in the older games of the series).

A very basic approach would be a bitmap image (B/W) where black pixels represent air and white pixels represent ground. Destruction of the landscape can be done easily using pixel operations. So if a rocket hits the ground, paint a black circle with radius = blastRadius at the point of impact.

You can then render your world (or just a portion of it) using that bitmap. For better performance I suggest you implement it in a way, that you can update/render just a portion of the “world”. Eg. if some parts of the landscape are destroyed by a rocket, just re-render the affected areas, not the whole world.

Instead of a B/W image as your “collision-map”, you could also use a 24bit image where you use two channels to store the surface-normal (x,y) per pixel and one channel to store the actual “collision-map”. Having the surface-normal at hand will greatly help you to calculate bouncing grenades, or to determine if a character can move in a given direction.

One possibility off the top of my head:

Use a vector graphics path representation for storing the outline of the destructible “land”. When a destruction event occurs (e.g., a grenade goes off), the blast area, represented as a circle, would be removed from the the land path via a boolean subtraction operation. The resulting path represents the new “land” for ground collision detection, and also possibly a mask for drawing the land.

Use constructive solid geometry

I wrote a proof of concept that used constructive solid geometry to handle destructible terrain. I used the GLU Tessellator to perform the boolean operations. The documentation explains how, search for “CSG Uses for Winding Rules”.

I fed the triangle output of the tessellator as static polygons into Box2D. The PoC worked quite well. I was able to arbitrarily subtract and add terrain in real-time and the terrain continued to behaved appropriately with Box2D. The only real hiccup was that the GLU tessellator can produce degenerate triangles which Box2D doesn’t like, so I had to filter those out by hand.

The next step in the PoC (which I never got around to) was to use the SCC algorithm from the boost graph library to detect when a piece of the terrain had been severed (cut the top off a mountain). The severed terrain would still be destructible but now represented by a dynamic(non-static) Box2D body with the triangles attached as shapes. I had the design worked out but lost interest once I started digging into the boost documentation. I “plan” to revisit the idea when I make a scorched earth/Worms game someday.

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