Quake 2 PVS, Realigned Lightmaps and Colour Lightmaps

Friday, 10th August 2007

Quake 2 stores its visibility lists differently to Quake 1 - as close leaves on the BSP tree will usually share the same visibility information, the lists are grouped into clusters (Quake 1 stored a visibility list for every leaf). Rather than go from the camera's leaf to find all of the other visible leaves directly, you need to use the leaf's cluster index to look up which other clusters are visible, then search through the other leaves to find out which reference that cluster too.

In a nutshell, I now use the visibility cluster information in the BSP to cull large quantities of hidden geometry, which has raised the framerate from 18FPS (base1.bsp) to about 90FPS.

I had a look at the lightmap code again. Some of the lightmaps appeared to be off-centre (most clearly visible when there's a small light bracket on a wall casting a sharp inverted V shadow on the wall underneath it, as the tip of the V drifted to one side). On a whim, I decided that if the size of the lightmap was rounded to the nearest 16 diffuse texture pixels, one could assume that the top-left corner was not at (0,0) but offset by 8 pixels to centre the texture. This is probably utter nonsense, but plugging in the offset results in almost completely smooth lightmaps, like the screenshot above.

   
Before and after - coloured lightmaps.

I quite like Quake 2's colour lightmaps, and I also quite like the chunky look of the software renderer. I've modified the pixel shader for the best of both worlds. I calculate the three components of the final colour individually, taking the brightness value for the colourmap from one of the three channels in the lightmap.

float4 Result = 1;

ColourMapIndex.y = 1 - tex2D(LightMapTextureSampler, vsout.LightMapTextureCoordinate).r;
Result.r = tex2D(ColourMapSampler, ColourMapIndex).r;

ColourMapIndex.y = 1 - tex2D(LightMapTextureSampler, vsout.LightMapTextureCoordinate).g;
Result.g = tex2D(ColourMapSampler, ColourMapIndex).g;

ColourMapIndex.y = 1 - tex2D(LightMapTextureSampler, vsout.LightMapTextureCoordinate).b;
Result.b = tex2D(ColourMapSampler, ColourMapIndex).b;

return Result;