[dx12] Increase max RTV allocations (or make it configurable).

[dati91]

gfx/src/backend/dx12/src/lib.rs

Line 497 in 281e798

let max_rtvs = 256; // TODO

To run our test suite, we need more rtv allocated. Currently it is (a constant) 256.

[msiglreith]

We need a way to handle these cpu descriptors in the longer term:

1. (Currently used in rostkatze): Having a vector of fixed size cpu descriptor heads which will be filled up.
   Pro: Easy to implement
   Cons: Requires synchronization, additional work required to quickly check for free spaces

2. Dynamically allocate cpu descriptor heaps on demand, motivated by the fact that cpu descriptor heaps are basically just designed to mirror the gpu heaps (nicer design). In particular, interesting for RTV and DSV as they are only needed for framebuffers, so have a fixed scope and can be batched together in case of multiple attachments. Only other use case for RTV and DSV would be depth clearing images outside of renderpasses, where we only specify an image and subresource range. This requires creating a RTV/DSV on the fly, but one might argue that these functions are slow-path.

[zakorgy]

Could we temporary bump the max_rtvs value to 2048 and max_dsv to 128, until the proper solution is shipped? These are the minimum limits we need to run all the wrench tests without fail.

[kvark]

@zakorgy we certainly should, yeah

[msiglreith]

dEQP-VK.texture.filtering.cube.formats.a1r5g5b5_unorm.nearest_mipmap_linear fails due to running out of samplers.