# Objective
- The #7064 PR had poor performance on an M1 Max in MacOS due to significant overuse of registers resulting in 'register spilling' where data that would normally be stored in registers on the GPU is instead stored in VRAM. The latency to read from/write to VRAM instead of registers incurs a significant performance penalty.
- Use of registers is a limiting factor in shader performance. Assignment of a struct from memory to a local variable can incur copies. Passing a variable that has struct type as an argument to a function can also incur copies. As such, these two cases can incur increased register usage and decreased performance.
## Solution
- Remove/avoid a number of assignments of light struct type data to local variables.
- Remove/avoid a number of passing light struct type variables/data as value arguments to shader functions.
# Objective
add spotlight support
## Solution / Changelog
- add spotlight angles (inner, outer) to ``PointLight`` struct. emitted light is linearly attenuated from 100% to 0% as angle tends from inner to outer. Direction is taken from the existing transform rotation.
- add spotlight direction (vec3) and angles (f32,f32) to ``GpuPointLight`` struct (60 bytes -> 80 bytes) in ``pbr/render/lights.rs`` and ``mesh_view_bind_group.wgsl``
- reduce no-buffer-support max point light count to 204 due to above
- use spotlight data to attenuate light in ``pbr.wgsl``
- do additional cluster culling on spotlights to minimise cost in ``assign_lights_to_clusters``
- changed one of the lights in the lighting demo to a spotlight
- also added a ``spotlight`` demo - probably not justified but so reviewers can see it more easily
## notes
increasing the size of the GpuPointLight struct on my machine reduces the FPS of ``many_lights -- sphere`` from ~150fps to 140fps.
i thought this was a reasonable tradeoff, and felt better than handling spotlights separately which is possible but would mean introducing a new bind group, refactoring light-assignment code and adding new spotlight-specific code in pbr.wgsl. the FPS impact for smaller numbers of lights should be very small.
the cluster culling strategy reintroduces the cluster aabb code which was recently removed... sorry. the aabb is used to get a cluster bounding sphere, which can then be tested fairly efficiently using the strategy described at the end of https://bartwronski.com/2017/04/13/cull-that-cone/. this works well with roughly cubic clusters (where the cluster z size is close to the same as x/y size), less well for other cases like single Z slice / tiled forward rendering. In the worst case we will end up just keeping the culling of the equivalent point light.
Co-authored-by: François <mockersf@gmail.com>
# Objective
- Builds on top of #4901
- Separate out PBR lighting, shadows, clustered forward, and utils from `pbr.wgsl` as part of making the PBR code more reusable and extensible.
- See #3969 for details.
## Solution
- Add `bevy_pbr::utils`, `bevy_pbr::clustered_forward`, `bevy_pbr::lighting`, `bevy_pbr::shadows` shader imports exposing many shader functions for external use
- Split `PI`, `saturate()`, `hsv2rgb()`, and `random1D()` into `bevy_pbr::utils`
- Split clustered-forward-specific functions into `bevy_pbr::clustered_forward`, including moving the debug visualization code into a `cluster_debug_visualization()` function in that import
- Split PBR lighting functions into `bevy_pbr::lighting`
- Split shadow functions into `bevy_pbr::shadows`
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## Changelog
- Added: `bevy_pbr::utils`, `bevy_pbr::clustered_forward`, `bevy_pbr::lighting`, `bevy_pbr::shadows` shader imports exposing many shader functions for external use
- Split `PI`, `saturate()`, `hsv2rgb()`, and `random1D()` into `bevy_pbr::utils`
- Split clustered-forward-specific functions into `bevy_pbr::clustered_forward`, including moving the debug visualization code into a `cluster_debug_visualization()` function in that import
- Split PBR lighting functions into `bevy_pbr::lighting`
- Split shadow functions into `bevy_pbr::shadows`
