Headless rendering to images

[cart]

The RenderGraph should already be able to handle headless rendering scenarios. The only missing pieces are:

• Adapt WindowTextureNode to a TextureNode, which produces a texture output for configured dimensions instead of window dimensions
• Write code to copy texture data from the gpu to an image file so headless rendering can be verified

[rmsc]

It definitely does: https://github.com/mrk-its/bevy/tree/render_to_texture and https://github.com/rmsc/bevy/tree/render_to_file.

There are however a few open questions, namely:

• The Camera system expects a WindowId. Maybe change that to an enum to also support a TextureId?
• There is a Res<Windows> for WindowId-to-Window mapping, perhaps there should also be one for TextureId-to-Texture?
• To me it's not clear how to properly interface with the ECS to move the texture from the GPU to the CPU (possibly also related to Distinguish between "GPU textures" and "CPU textures" #1234)

[alice-i-cecile]

Complete! See #1927.

[mockersf]

Complete! See #1927.

Not really. It's not possible to render to an image file as the issue was saying

[DGriffin91]

I made a little example of this awhile back. If it would be helpful, I could update it.

Write code to copy texture data from the gpu to an image file so headless rendering can be verified

Are we looking for an example or a test here?

[mockersf]

Nice!

Ideally we would need to have a nice api in Bevy to:

• move data from gpu to cpu
• move data from render app to main app

It could maybe be a more "hardcoded" capture plugin as you have in your example, that could already be useful...

[hymm]

Fixed in #7163

[mockersf]

@hymm does it work in headless mode? this issue was kept for that

[hymm]

probably not. will reopen.

edit: saw this message #7163 (comment) and thought it was fixed.

[bes]

Hello! Would this also cover the case where a pure headless pipeline could be built by outputting to a OpenGL (or Vulkan) texture?

Specifically, I am looking to do something like

              -------
Texture  --> | Bevy | --> Texture
              -------

Where Texture is a native (OpenGL, Vulkan) texture that can be fed into Bevy and then I can get a native texture out of Bevy (I expect there to be some manual wgpu steps involved, too).

I guess wgpu needs to be able to handle native textures in / out (which I don't think it does currently).

So for the Bevy part I think what's most important is to be able to render to a texture (and not be limited to an image on file).

I already have custom, non-Bevy, pipeline doing this, but there are a lot of unsafe { gl::... calls going on 😅, so getting this all into bevy would be a dream come true.

[jeertmans]

Hello! Is there any update on this?
I would be super interested in being able to use bevy_image_export in headless more :-)

[DGriffin91]

@jeertmans #5550 runs without a window. It may or may not be a helpful reference.

[jeertmans]

Thanks, @DGriffin91! I'll take a look at it when I have some time :-)
I'm quite new to Bevy, so I might reach back to you for questions ^^'