Fire Color RGB

[tommygdawg]

Hey all

Is it possible to color the fire/flames from Phoenix with the RGB from a PHX Source? Following that, is it possible to change the color of the fire based on some kind of scene trigger?

Thank you!

[georgi.zhekov]

Hey,

Absolutely, you can use the RGB channel for the color of the fire. You just need to set the Based on option for the Fire to the RGB channel in the Rendering rollout of the Simulator > Volumetric Options > Fire settings.
Just make sure that the RGB channel is enabled in the Output rollout of the Simulator before running the simulation.

The next thing you need to do is set the Fire opacity mode in the Volumetric Options to either Fully Visible or Use Smoke opacity.

A note that when using the RGB channel for the Fire color - the GPU preview in the viewport won't show anything - support for that is still in the to do list. It will render correctly though.

As for more control you can check this video here that covers how to use the Voxel Tuner - https://youtu.be/mGAyh3uR89U?si=qtUiQAczwG4jMBVA&t=850

Cheers!

[tommygdawg]

Thank you Georgi! thought this was the case, but when I set the fire color to RGB, it no longer renders. What am I doing wrong?

[zdravko_pavlov1]

Are you using Vray GPU? Does it render with the CPU?

[georgi.zhekov]

Could it be that it's too weak - maybe you need a higher fire multiplier? Do you have any lights in the scene besides the fire?

[tommygdawg]

I do have lights in the scene. I've also tried GPU and CPU both to no avail. I've also increased the fire multiplier to ridiculous numbers like 100. Could it be that I'm using a Phoenix nightly build since I'm on Max 2025?

[georgi.zhekov]

It should be working fine in Max 2025. How about if you switch the Fire Opacity mode to Use Smoke Opacity and for the Smoke Opacity you use the Temperature channel?

Can you send over the scene so that we can take a look?

You can attach it here as a zip file or send it via support.chaos.com (submit a request at top right).

[tommygdawg]

Further updates. I've made a blank simple scene with a sphere emitter only just to make life easier. That's also not working. But I discovered that emitting smoking makes a huge difference in the RGB channel preview in the simulator. This is what the RGB channel looks like without smoke:

And with:


Okay cool. So RGB follows smoke. Neat! However when I set fire to RGB now, it works, but it simply looks like smoke instead of flames (this is with the fully visible option):



I can set it to smoke opacity, and then set the smoke to temperature. But then, what would I do if I wanted to also render smoke with the smoke channel?

[georgi.zhekov]

Yes, with the Fully Visible mode you won't be able to control the curve. Use Smoke opacity will give you more control.

In case you want to render smoke as well - you can create a Voxel Shader, pick the simulator in it and from the Volumetric Rendering options, disable the Fire rendering (as it already comes from the simulator itself) and dial in your Smoke options as needed.
You can find more about the Voxel Shader here - https://docs.chaos.com/display/PHX4MAX/Voxel+Shader