GPUParticles3D: Translate inactive particles to -INF

[ecmjohnson]

Resolves #72650 by translating inactive particles to negative infinity. This solution was proposed by @Calinou in this comment. Note that this is an alternate to #75090 and only one is needed.

[QbieShay]

Thank you for the PR! Could you test with trails enabled?

[Calinou]

Thank you for the PR! Could you test with trails enabled?

Trails will most likely exhibit the issue where they appear to go towards negative infinity (this already occurs with Hide on Contact collision). This needs a special case to avoid connecting the trail somehow, but I don't know how this could be done.

[ecmjohnson]

I tried to setup a scene with trails enabled:

1. create a new GPUParticles3D node in the scene
2. under Trails check Enabled
3. add a TubeTrailMesh (the caution symbol seemed to want this or RibbonTrailMesh) under Pass 1
4. give it a new StandardMaterial3D
5. under Billboard change Mode to Enabled
6. under Transform check Use Particle Trails
7. add a new ParticleProcessMaterial

Results before this change:

Results after this change:

It doesn't appear that they are connecting to negative infinity or the origin, but I'm not totally sure what I'm seeing or if I've set them up properly. I'm not too familiar with the particles trails feature, or particles as a whole tbh. @QbieShay do you have a scene I can use for regression or point me to more information on GPUParticles3D trails?

[ecmjohnson]

Is it expected that billboarding and trails features work together? They don't seem to behave as I would expect.

For an example trail particle system, with billboarding disabled:

Becomes the following when billboard mode is set to Particle Billboard:

It seems they aren't billboarding to face the camera:

[QbieShay]

There's an extra trail property in the drawing tab of the particle system. Additionally trails need a skinned mesh. Setting them up is a bit complicated right now.

[clayjohn]

Looks good! The same change is needed for the OpenGL renderer here:

godot/drivers/gles3/shaders/particles_copy.glsl

Line 48 in d4dad2b

mat4 txform = mat4(vec4(0.0), vec4(0.0), vec4(0.0), vec4(0.0)); // zero scale, becomes invisible.

I think once the fix is added to OpenGL we can go ahead and merge. I am not 100% sure this will fix the issue on all devices as -1.0 / 0.0 is not guaranteed to be inf it is simply undefined.

If we have issues with this fix we can switch to using #define FLT_MAX 3.402823466e+38 instead

[ecmjohnson]

I actually did some research on the correctness of this method of generating an infinity before using it and it is correct for the GLSL #version 450 specified according to this answer; however, the change for GLES3 cannot use it reliably so for that I used the FLT_MAX approach instead. I verified that the GLES3 change resolved #72650 for the "Compatibility" renderer

[clayjohn]

Looks good!

[akien-mga]

Thanks! And congrats for your first merged Godot contribution 🎉

[YuriSizov]

Cherry-picked for 4.0.3.