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# 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.
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