Skewed output when changing resolution of new headless_renderer example

[cxreiff]

Bevy version

main
v0.14.0-dev
f91fd32

Relevant system information

rustc/cargo 1.78.0

`SystemInfo { os: "MacOS 14.4.1 ", kernel: "23.4.0", cpu: "Apple M2 Max", core_count: "12", memory: "96.0 GiB" }`
`AdapterInfo { name: "Apple M2 Max", vendor: 0, device: 0, device_type: IntegratedGpu, driver: "", driver_info: "", backend: Metal }`

What you did

Hello all - I am taking a look at the new headless_renderer example in the repo: https://github.com/bevyengine/bevy/blob/main/examples/app/headless_renderer.rs
#13006

I have a use case where I would need to set the dimensions of the output image based on something outside of bevy. So I ran the example after changing the configured dimensions (on line 69 in the AppConfig struct).

What went wrong

I expected the output image to be properly formatted at the indicated resolution. However, just changing the width by 1 or a few results in output that is skewed/misaligned (examples attached).

I sort of suspected that this had to do with bevy's default output, which doesn't match the resolution in the example but does have the same aspect ratio. So I changed the primary_window in WindowPlugin from None to a window with the config-defined dimensions:

primary_window: Some(Window {
  resolution: WindowResolution::new(config.width as f32, config.height as f32),
  ..default()
}),

...but it didn't change the output at all (and in fact no window appears, I assume because the camera's target is still set to a texture).

Additional information

I assume its most likely some kind of bit alignment issue where the resolution needs to be a certain aspect ratio or along certain increments, but I tried changing the width by increments of 4, 8, etc, and had no luck.

Thank you.

[cxreiff]

The AppConfig struct is where I started, I just decreased the width by one, e.g. on line 68-72:

let config = AppConfig {
        width: 1919,
        height: 1080,
        single_image: true,
};

...which results in the 45° skewed image (second screenshot). I also tried adding 4, 8, 16, and 32 to the width to see if that worked, and it didn't- but just now I tried adding 64 (1952x1080) and it worked! So it seems that the width has to be multiples of 64. It wouldn't be a problem for most fixed resolutions but for my use case a user might resize it to anything.

[bugsweeper]

If found the root of problem. That is in copying from image to buffer, because copy_texture_to_buffer can copy image only by rows aligned wgpu::COPY_BYTES_PER_ROW_ALIGNMENT. That is why image in buffer can be little bit wider. I will fix copying from buffer to resulting image.

[cxreiff]

Oh great! I tried digging but wgpu calls are a bit beyond me at the moment. Thanks for your help!

[bugsweeper]

@cxreiff Done