# Lighting

## Forward

```
for each triangle:
    for each pixel:
        for each light:
            shade(pixel, light)
```

- Overdraw penalty.
- Client must specify all lights (for the object) up front.

## Deferred

### Forward Pass

The forward pass generates:
- Depth
- Texture ID
- Texture coordinates

Sampling of textures is deferred to avoid overdraw penalty.

### Pixel-centric Shading

```
for each pixel:
    for each light:
        shade(pixel, light)
```

- Need a pixel-in-volume test.
- Inefficient if most pixels are not affected by a light.
  - Ok:  ambient, directional.
  - Bad: point, area.

### Light-centric Shading

```
for each light:
    volume <- project light volume
    for each pixel in volume:
        shade(pixel, light)
```

- Need to project the light volume.
- Shades only the pixels that are covered by the volume.
- For ambient and directional, the volume is all space.

## Clustered

### Cluster Generation

```
for each light:
    volume <- project light volume to NDC
    for each cluster:
        test(cluster, volume)
```

- Need a volume-AABB test (the cluster is an AABB in NDC space.)
- Lighting then proceeds as in deferred.