Geometry Shader - for subd of dyn mesh

[JeffGillin]

Describe the project you are working on

Any game with lots of dynamic mesh generation.

Describe the problem or limitation you are having in your project.

Subdivision of dynamic mesh (subdivision would be too slow if cpu bound).

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

Geometry shaders to subd a mesh within shader instead of godot code

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

Another shader function named "geometry()" that would allow you to add/remove mesh data.

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

Could probably be worked around with gpu compute, but then dealing with 2 passes to gpu (one to compute subd, and one to render). Geometry shader wouldn't require second call.

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

Yeah, part of the shader language ...

[fire]

The game graphics industry consensus is that you create tessellation using compute shaders and not tessellation stages and definitely not geometry shaders. I can go into more detail. Its related to the fact you can not create new geometry.

[SIsilicon]

@fire Please go into more detail. I'd like to know more.

[fire]

Have to do things but here is a article. http://www.joshbarczak.com/blog/?p=667

[clayjohn]

Most GPUs offload the geometry shader stage to the CPU which creates huge CPU and bandwidth bottlenecks on anything but the simplest demo projects. For that reason, we have decided in the past not to add support for them.

[Calinou]

See also #784.

[Chaosus]

There was even the implementation by me godotengine/godot#28237. If you really need them you can rebase this PR and recompile the engine.

This proposal has no way to realize. @reduz said the points of why:

• Geometry shaders are being deprecated in modern API versions. They are inefficient and can be better replaced with Compute.
• Geometry shaders are not well supported in modern hardware. They remain there for compatibility but they are not very efficient.
• Godot uses OpenGL ES 3.0, which does not support them, so they won't work on mobile.
• There is not high demand for the feature.

[Calinou]

Closing, as geometry shaders will not be implemented in 4.0 or later given they are deprecated and not present in Vulkan. See also #2075 (comment).