Hi, everyone! I teach Intro to Houdini, and last fall I taught my students how to create fiery smoke trails in an explosion, using the Secondary Fire option in XPU Pyro Preview material. It was super-easy, since it relied on a separate trail_temperature attribute, and the resulting glowing tips existed separately from the main explosion's temperature field, and did not get covered in smoke - not even when the "fire mask" option was engaged. (This was in H19.5)

I'm trying to teach the same procedure now, using H20, but the Secondary Fireis now missing from all the pyro-shading materials. (Karma Pyro Material, Karma Pyro Shader, Karma Explosion Pyro Material etc.

(I suppose I can assign those little glowing tips a regular temperature attribute, so that they will get shaded fiery along with the main explosion fire, but then they get completely covered whenever I engage the Fire Masking option)

Halp?

Update: Apparently Secondary Fire option is still alive and well inside a Pyro Advanced Shader - AND Pyro Advanced Shader appears to work with Karma. But only Karma CPU. NOT Karma XPU.

Well then...

Atilla explains the new Pyro Shader here https://youtu.be/lXzkxlnQErQ?t=2906 [youtu.be]
starts at 48:26 and at 49:13 he explains the decision why Secondary Fire was removed and what to use instead (49:51)

essentially use the new Karma Fire Emission node to do your secondary, tertiary, etc fire emission

Hi Tomas and big thanks for the explanation link!

My fire trails are now appropriately fiery :-) I only ran into one trouble: when I tried to bind trail_temperature to the color volume/intensity volume inside the Karma Fire Emission node, the drop-down selection menu wouldn't let me select trail_temperature (it didn't show up as one of the options). However, I typed trail_temperature in the selection field manually, and somehow, it worked :-p!

(I needed to separate the trail_temperature from the overall temperature in order to mask the main explosion fire, but leave the fiery trail heads unmasked!)

Hopefully I understood everything correctly! Thank you again for your help!

Inna