Explain parameter usage in GPUParticles3D and GPUParticles2D

[thmasn]

extended the description to explain how the passed parameters are used by the default ParticleProcessMaterial.
should set correct expectations for issues like 85358

[thmasn]

how can this simple text change fail a check?
the brackets are used in other descriptions too, there are no special characters.
i assume the failed check for linux w/ mono has an external reason?
this is my first commit here, so i am unsure how this works.

[akien-mga]

@thmasn See the review comment by @AThousandShips above. There are spaces at the end of the line that should be removed (and she suggested adding a word too, though that part is not what causes the CI error, the trailing spaces are).

Note: Please make modifications by amending the commit, and force pushing the changes, so that it stays as a single commit (see PR workflow). While doing this, you should also amend the commit message to be more explicit (e.g. like the PR title).

Alternatively, a maintainer can also update your PR branch directly to do those improvements.

[thmasn]

i think i fixed it:

• trailing spaces are removed
• it is reduced to one commit with the correct title

[akien-mga]

There's a similar API in GPUParticles2D, so it sounds like the same changes should be made there?

Aside from my comment on the form, I can't really evaluate whether the actual content is accurate, would be good to get input from @QbieShay

As a side note, this custom parameter could now use Vector4 instead of Color. But that's outside the scope of this PR and probably not worth changing until Godot 5 to avoid unnecessarily breaking compatibility. But the use of Color as a container for 4 scalars predates the introduction of the Vector4 type.

[thmasn]

i modified the text to also use the code-tag. i would favor the "use" word over "map", as the properties stay inside the vector4, and are maintained in this form.
and true, the way i understand it, GPUParticles2D uses the same ProcessMaterial, so the comment is valid for both.

i again amended the commit to match these changes.

[QbieShay]

It will overwrite both custom and color

[thmasn]

It will overwrite both custom and color

yes, both are updated each frame in the processMaterial.

but, it seems to me like the intial parameters passed in custom still matter though: p.e. when you pass a lifetime of 0.0, or an age greater than the lifetime, the particle dies instantly.
on the other hand, the color that is beeing passed is instantly overriden, and therefore does not have any visible effect with the default processmaterial.

[QbieShay]

Oooh good catch!

[YuriSizov]

Thanks! And congrats on your first merged contribution to the engine!