Particle Shader Descriptions

[emirljuca]

Your Godot version:
4.1

Issue description:

Particle Shaders descriptions are not substantial enough. For example, the TRANSFORM description is: "Particle transform." I have no idea really what this means but looking online there is some information about the rotation, position, sheer and size but the documentation does not talk about this at all.

However, what I really need documentation on is the emit_subparticle. Could the creators expand on, what the inputs are, xform, and custom does not give any information. "Forces to emit a particle from a sub-emitter." Does that mean just a single particle? How can we emit GPU particles where the GpuParticles.Amount > 1?

URL to the documentation page (if already existing):
https://docs.godotengine.org/en/stable/tutorials/shaders/shader_reference/particle_shader.html#process-functions

[Calinou]

Could the creators expand on, what the inputs are, xform, and custom does not give any information. "Forces to emit a particle from a sub-emitter."

In programming, "xform" is a common shorthand form that means "transform". In this context, a transform is a 3D transform which is a 3×4 matrix that specifies the position (as the origin) and the orientation (as the basis). The GLSL type we use for transforms is mat4: https://docs.godotengine.org/en/stable/tutorials/shaders/shader_reference/shading_language.html#uniforms

When a Transform3D is used, the w Vector is set to the identity.

The custom data field can be used to specify additional per-data information the shader can make use of. You can leave this empty if you don't need it.

Does that mean just a single particle? How can we emit GPU particles where the GpuParticles.Amount > 1?

You should be able to call emit_subparticle() several times per process() call using a for loop.

[emirljuca]

That makes a lot of sense, thank you! However, I think this description you made should be in the particle shader document to clarify what each inputs are and how to use the emit_subparticle more effectively. I was also wondering, if I use the FLAG_EMIT_VELOCITY, does that overwrite the velocity of the sub particle during the start step? I have found that this does seem to be the case..