# Objective
Upgrade to `wgpu` version `25.0`.
Depends on https://github.com/bevyengine/naga_oil/pull/121
## Solution
### Problem
The biggest issue we face upgrading is the following requirement:
> To facilitate this change, there was an additional validation rule put
in place: if there is a binding array in a bind group, you may not use
dynamic offset buffers or uniform buffers in that bind group. This
requirement comes from vulkan rules on UpdateAfterBind descriptors.
This is a major difficulty for us, as there are a number of binding
arrays that are used in the view bind group. Note, this requirement does
not affect merely uniform buffors that use dynamic offset but the use of
*any* uniform in a bind group that also has a binding array.
### Attempted fixes
The easiest fix would be to change uniforms to be storage buffers
whenever binding arrays are in use:
```wgsl
#ifdef BINDING_ARRAYS_ARE_USED
@group(0) @binding(0) var<uniform> view: View;
@group(0) @binding(1) var<uniform> lights: types::Lights;
#else
@group(0) @binding(0) var<storage> view: array<View>;
@group(0) @binding(1) var<storage> lights: array<types::Lights>;
#endif
```
This requires passing the view index to the shader so that we know where
to index into the buffer:
```wgsl
struct PushConstants {
view_index: u32,
}
var<push_constant> push_constants: PushConstants;
```
Using push constants is no problem because binding arrays are only
usable on native anyway.
However, this greatly complicates the ability to access `view` in
shaders. For example:
```wgsl
#ifdef BINDING_ARRAYS_ARE_USED
mesh_view_bindings::view.view_from_world[0].z
#else
mesh_view_bindings::view[mesh_view_bindings::view_index].view_from_world[0].z
#endif
```
Using this approach would work but would have the effect of polluting
our shaders with ifdef spam basically *everywhere*.
Why not use a function? Unfortunately, the following is not valid wgsl
as it returns a binding directly from a function in the uniform path.
```wgsl
fn get_view() -> View {
#if BINDING_ARRAYS_ARE_USED
let view_index = push_constants.view_index;
let view = views[view_index];
#endif
return view;
}
```
This also poses problems for things like lights where we want to return
a ptr to the light data. Returning ptrs from wgsl functions isn't
allowed even if both bindings were buffers.
The next attempt was to simply use indexed buffers everywhere, in both
the binding array and non binding array path. This would be viable if
push constants were available everywhere to pass the view index, but
unfortunately they are not available on webgpu. This means either
passing the view index in a storage buffer (not ideal for such a small
amount of state) or using push constants sometimes and uniform buffers
only on webgpu. However, this kind of conditional layout infects
absolutely everything.
Even if we were to accept just using storage buffer for the view index,
there's also the additional problem that some dynamic offsets aren't
actually per-view but per-use of a setting on a camera, which would
require passing that uniform data on *every* camera regardless of
whether that rendering feature is being used, which is also gross.
As such, although it's gross, the simplest solution just to bump binding
arrays into `@group(1)` and all other bindings up one bind group. This
should still bring us under the device limit of 4 for most users.
### Next steps / looking towards the future
I'd like to avoid needing split our view bind group into multiple parts.
In the future, if `wgpu` were to add `@builtin(draw_index)`, we could
build a list of draw state in gpu processing and avoid the need for any
kind of state change at all (see
https://github.com/gfx-rs/wgpu/issues/6823). This would also provide
significantly more flexibility to handle things like offsets into other
arrays that may not be per-view.
### Testing
Tested a number of examples, there are probably more that are still
broken.
---------
Co-authored-by: François Mockers <mockersf@gmail.com>
Co-authored-by: Elabajaba <Elabajaba@users.noreply.github.com>
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