penberg / godoom Goto Github PK

Enemies, obstacles, and other things in Doom are rendered as sprites. In the WAD file, things have a position, angle, type, and options. The sprite is determined by the type, with mapping hardcoded to DOOM.EXE, apparently. Options specify what difficulty level a thing appears in, for example.

Doom uses an esoteric concept of "visplanes" to render flats, i.e., floors and ceiling. However, the approach is not useful when rendering with OpenGL, which is why the iPhone port tessellates floors and ceilings from sectors with the libtess library, as discussed in Fabian Sanglard's blog post. Unfortunately, there does not seem to be such library available for Go.

One possible solution is to follow the approach Rust Doom takes. We can triangulate subsector sector vertices as a triangle fan because the vertices are guaranteed to be convex because of the BSP partitioning. The only complication here is that we also need to include any subsector intersection points with the BSP partitioning segment. We need to do this to ensure we fill the whole subsector because there are no guarantees that the subsector has segments covering the edges of the subsector.