DX12 Push Constant out of bound

[abdo643-HULK]

Description
I think I found an issue with the current implementation of DX12 push constants. Currently if I try to use anything bigger than 64 bytes wgpu panics but from the docs and also the limits I should be able to use more. I think the problem is how the offset is currently used/calculated on this line.

wgpu/wgpu-hal/src/dx12/command.rs

Line 890 in e6314c4

self.pass.constant_data[(offset as usize)..(offset as usize + data.len())]

The offset is the one originally passed in from the renderpass and that's in bytes but root constants are expected to use 4 byte offsets.

I think a fix for the issue could look something like this:

self.pass.constant_data[((offset / 4) as usize)..((offset / 4) as usize + data.len())]
          .copy_from_slice(data);

Repro steps
This is the project where I able to produce the issue.
https://github.com/abdo643-HULK/Bachelor-Thesis/tree/main/source-code/app

Expected vs observed behavior
Expected: Just pass the offset in bytes like for the Vulkan backend.
Observed: DX12 uses incorrect size/offset.

Extra materials

Platform
OS: Windows 11 (build 22621.1778)
wgpu: 0.16.1

This is my first real bug report I hope this is helpful.

[initial-algebra]

Confirming that with wgpu 0.18 on Windows 11 (22621.2428) using the DX12 backend, setting push constants doesn't work correctly with a non-zero offset.

let width_bytes = self.width.to_le_bytes();
let height_bytes = self.height.to_le_bytes();
let push_constants_bytes = [
	width_bytes[0],
	width_bytes[1],
	width_bytes[2],
	width_bytes[3],
	height_bytes[0],
	height_bytes[1],
	height_bytes[2],
	height_bytes[3]
];
render_pass.set_push_constants(wgpu::ShaderStages::VERTEX_FRAGMENT, 0, &push_constants_bytes);

The preceding code works fine, but the following code works only with Vulkan.

render_pass.set_push_constants(wgpu::ShaderStages::VERTEX_FRAGMENT, 0, &self.width.to_le_bytes());
render_pass.set_push_constants(wgpu::ShaderStages::VERTEX_FRAGMENT, 4, &self.height.to_le_bytes()); // is read as 0 by the shader

However, I do not experience panicking or validation errors, even though the push constant size limit is set to 8 bytes.

[cwfitzgerald]

The offset problem is fixed by #4607 (found it while testing gl), I'm not sure about the out of bounds issue.

[cwfitzgerald]

The offset problem is fixed by #4607, I'm not sure about the out of bounds issue.

[cwfitzgerald]

I think they're the same problem