Ability to produce geometry or passes from shaders/materials?

[Zylann]

Maybe the title is not clear enough, but I'll explain:

Multi-pass:
Coming from Unity, I saw it's possible to tell an object to render twice or more only from its shader. For example, it allows to implement 3D outlines easily (draw mesh a second time, but extrude along normals, reverse normals and put it on an opaque pass), perform fur shading by duplicating layers of geometry in parts needing that, or implementing other cool effects that cannot be done in another way.
In Godot, shaders don't go beyond being shaders in the strict term of it. They cannot tell how many passes it has to be rendered properly. Because of that, the node must be duplicated (and then processed twice), or a script has to be added, a self-contained material is not enough. Could such capability be considered in the future?

Geometry generation:
Going a bit further, possibly different area. I know it's possible today to generate geometry from shaders, and so not being forced to do it on the CPU, client-side towards the graphic card. For example, send a low-poly terrain on the graphic card, and subdivide it dynamically on the GPU (is tesselation the right word?). I know this is a fairly advanced topic and might not be supported by some graphic cards, but would it be possible to use it in Godot in the future?

[SuperUserNameMan]

about multipass shader, just for reference : #4084

[vnen]

Also about multipass: #862.

[bojidar-bg]

Would this be considered for 3.0?

[ghost]

First of all thank you for your report and sorry for the delay.

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[Zylann]

The part about geometry has a specific issue: #10817

Multipass miiight be solved by the next pass system in materials, however it's not available with ShaderMaterials for some reason.

[vnen]

It is available in ShaderMaterial (you have to set a shader before it appears):

[ghost]

@vnen that option disappears when loading shader from file. is it intentional?

Edit: apparently next_pass only works with spatial type ShaderMaterial. My shader file was canvas_item type.

[eon-s]

Canvas item shaders and materials seems to not allow multiple passes, I have no idea if is intentional or not.

[akien-mga]

Since geometry shaders are handled in #10817 and multi-pass is already supported, I think this issue can be closed. If other parts remain to be addressed, they're better served in a new issue opened against the master branch.