Delux mapping

1. What

The bumpmapping commonly used in real time applications requires a pass per light source in the scene (In the best case).  This works well as long as there aren't much light sources in the scene and you can model the light in the scene using directional or point lights.
This is often the case for dark indoor areas with low ambient levels, but outdoor areas require a lot of point light sources to simulate the "radiosity" in those scenes.
At first we used normal lightmapping to model the ambient light in Tenebrae.  This works fine but the disadvantage is that art that looks good with per pixel lighting looks flat and boring since there is no hard coded shading in them.  Adding hard coded shading on the other hand takes away some of the bumpmapping quality.
Or new solution is to use bumpmapping on the ambient lighting too. This is what we call delux mapping.

Hard coded lighting	Flat, for use with normal map

2. The Idea

Delux mapping works by adding an extra precalculated map (besides the lightmap) to the level file.  Just like the light map this map has unique information for every surface in the world.  Instead of storing a color it stores an (range compressed) vector that points to the incident light on that surface.
When you render the ambient pass of the surface instead of modulating the lightmap with the color map we use the following equation
((delux . normalmap ) * 0.5 + 0.5) * lightmap * color

No delux	With delux	Delux map

3. How to calculate the delux maps

Delux maps are calculated at the same time the light maps are calculated.  For every light that shines on the luxel we update the delux map.  This is done by averaging the tolight vector with a scale factor that is the brightness of the light's contribution on that luxel.
This light doesn't have to come from an actual light source.  It can be light bounced back into the scene by the walls, a surface that is emmitting light,...
Notes:

• What with surfaces that receive no light:
  We use the surface normal at that point but it should never be used anyway. (as the light map is black at that point)

4. How to render them

The delux maps store their vector in world space.  The biggest "problem" when rendering them is converting the world space vector to tangent space (to dot it with the normal map).  Normally we can convert to tangent space at the vertex level and then use a renormalization cube map or similar to renormalize them.  With delux maps this has to be done using per pixel math.  This makes it impossible to use on Geforce2 level hardware and makes it a 2 pass algorithm for Geforce4 level hardware.  On modern hardware (Radeon9500+ and Geforce Fx) this can easily be done in one pass.
Once the delux map is converted into tangent space we render it very similar to ordinary bumpmaps.

5. Problems and ideas

• De delux maps only offer an approximation for the tolight vector.  If multiple lights shine on the same surface they are incorrect. (but look much better than lightmapping)  This can be clearly seen in the shots below, when two lights shine on the same surface you get light from 2 sides which gives a very "deep" effect, with delux mapping you only have one shadowed side (away from whatever the tolight direction is at that point)
  This "shadow on one side" problem is countered by the dot *0.5 + 0.5 we use when we render the delux map, the downside of this  is that the bumps look flatter even if there is an very distinct tolight vector available (only one light or all the lights come from the same direction).  An addition would be to store the "force" term in the deluxmap's alpha channel.  This would somehow encode how much of the incident light on the surface comes from the delux direction and how much comes from the other directions (and should thus light the "shadowed" parts too)
• Delux maps are not limited to diffuse lighting only, you can calculate the half angle vector per pixel and do specular mapping too.
• Delux mapping can only be used for static geometry.  (Which you have light maps for)

Delux	Lightmap	Delux & Light	"Real" bumps

6. Contact

Charles Hollemeersch  (Questions on the engine side of things)
ydnar(Randy Reddig)  (Questions on the compiler side of things)

Thanks to
Willi Hammes (for the level textures)
James Hastings-Trew (for the "gargoyle" textures)