This adds correct object bounds estimation.
This works by creating an occupancy texture where one
bit represents one froxel. A geometry pre-pass fill this
occupancy texture and doesn't do any shading. Each bit
set to 0 will not be considered occupied by the object
volume and will discard the material compute shader for
this froxel.
There is 2 method of computing the occupancy map:
- Atomic XOR: For each fragment we compute the amount of
froxels **center** in-front of it. We then convert that
into occupancy bitmask that we apply to the occupancy
texture using `imageAtomicXor`. This is straight forward
and works well for any manifold geometry.
- Hit List: For each fragment we write the fragment depth
in a list (contained in one array texture). This list
is then processed by a fullscreen pass (see
`eevee_occupancy_convert_frag.glsl`) that sorts and
converts all the hits to the occupancy bits. This
emulate Cycles behavior by considering only back-face
hits as exit events and front-face hits as entry events.
The result stores it to the occupancy texture using
bit-wise `OR` operation to compose it with other non-hit
list objects. This also decouple the hit-list evaluation
complexity from the material evaluation shader.
## Limitations
### Fast
- Non-manifolds geometry objects are rendered incorrectly.
- Non-manifolds geometry objects will affect other objects
in front of them.
### Accurate
- Limited to 16 hits per layer for now.
- Non-manifolds geometry objects will affect other objects
in front of them.
Pull Request: https://projects.blender.org/blender/blender/pulls/113731
f79b86553a