Add support for asynchronous RenderingDevice.buffer_get_data() (hardware readbacks)

[nelstuff]

Describe the project you are working on

Voxel game mostly running on GPU using compute shaders.

Describe the problem or limitation you are having in your project

Every time I want to read something on the GPU from the CPU, it stalls the compute pipeline to have up to date data.
var output_bytes := rd.buffer_get_data(buffer)
The performance penalty is very high.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Asynchronous function to read data when it is ready (can be a few frames delayed), without stalling the pipeline. Unity uses this: https://docs.unity3d.com/ScriptReference/Rendering.AsyncGPUReadback.html

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

rd.buffer_get_data_async(gpu_buffer, cpu_readback)

func cpu_readback(read_bytes):
    # do somehitng with read_bytes

If this enhancement will not be used often, can it be worked around with a few lines of script?

Not that I know of

Is there a reason why this should be core and not an add-on in the asset library?

I don't believe you can write this in an addon?

[Calinou]

• Related to Implement threading to speed up video saving in Movie Maker mode #4751 and Add support for embedding the game window in the editor #7213.

[granitrocky]

Has anyone begun work on this? Is there somewhere I could contribute to? I would really like to see this added to Godot.