Deferred Lighting

Deferred lighting will help us overcome performance issues with large numbers of lights in a scene, and will also allow us to implement normal mapping, specular highlights, The description at http://www.infinity-universe.com/Infinity/index.php?option=com_content&task=view &id=105&Itemid=27 is a useful reference, as is the Panda3D Fireflies tutorial.

Buffer Layout

The G-Buffers (generic buffers) we'll be using are as follows:

	Red channel	Green channel	Blue channel	Alpha channel
Buffer 1	Basic lighting R	Basic lighting G	Basic lighting B	Depth
Buffer 2	Diffuse color R	Diffuse color G	Diffuse color B	Self-illumination
Buffer 3	Normal X	Normal Y	Velocity X	Velocity Y
Buffer 4	Extinction	?	Specular amount	Material ID

Basic lighting

Filled by a standard forward lighting pass

Depth

Filled with the contents of the depth buffer from the forward lighting pass

Diffuse color

The diffuse reflection color of the material at each pixel

Self-illumination

The self-illumination amount for the material at each pixel (illumination is performed by multiplying this by the diffuse color)

Normal

The X and Y components of the normal vector of the surface at each pixel (the Z component is calculated using sqrt(1 - X**2 - Y**2))

Velocity

The difference between the view-space coordinate of this pixel from last frame and the view-space coordinate of this pixel in the current frame (only X and Y components) - used for motion blur

Extinction

The atmospheric extinction value for this pixel (TODO: How is this determined? What does it depend on? How is it used?)

Specular amount

The amount of specular reflection of the surface at this pixel
Material ID: Used to determine which material to use for this pixel (this can change which BRDF equation is used, how the above fields are interpreted, etc)

If possible, all channels should be 16-bit floats.

A possible use for the remaining channel is to split the Extinction value into a red and blue component, generating the green component by averaging the two. That could possibly give us more accurate atmospheric scattering, but we'd have to look at what usual values for color extinction are.

Issues

There are several issues with using deferred lighting, listed below. Creative solutions welcomed.

Transparency

According to all the documentation I've been able to find, deferred lighting is incompatible with rendering transparent objects; they suggest rendering all transparent objects over top of the scene in a final pass, and using standard direct lighting on them. We may be able to make this slightly better by applying the nearest n lights (where n is the maximum number of lights the OpenGL implementation allows; generally rather small) to each transparent object when rendering.

Antialiasing

Deferred lighting is also incompatible with FSAA, or multisampling in general, according to everything I've found. This causes major visual glitches for things like power lines. The only proposed solution so far is to use edge detection and a blur filter as a post-processing step, but that won't fix missing pixels for very thin objects. (like power lines)