Rendering only fire in pyro2 with pyro shader

[cloudfx]

I was generating only the fire and there is only het and temperature field tht i am using for fire tab od pyro shader. Turned off 'emit smoke' so there is no data in density channel. With that setting, it renders nothing.

[lukeiamyourfather]

By default the opacity is linked to the density if I remember correctly (don't have it in front of me to check). You can link the opacity to the temperature instead so the hotter areas are more opaque.

[Scratch]

Pyro needs Density in order to simulate, even if you are not interested in smoke.

EDIT: not so sure about that anymore.

This is how you get fire without smoke (serveral possibilities):

1) You solve the problem within the shader:

Simulate smoke AND fire, and then go to the pyro shader. There, move to the the Smoke Tab and go to Density. Now you have 2 Options. You can go to fit to range -> target range, and set both values to 0. This means that all the incoming density values will be remapped to be between zero and zero...which makes them...well...zero. And zero density menas no smoke gets rendered (even if it is there in the simulation.) The second method is - if you are using the ramp (which is on by default) - to lower the second ramp keyframe to zero, which does the same thing as explained above (control the mapping of the density), but gives you more control (e.g you could have a specific curve to tell houdini how the mapping should happen.) Using the above option will allways interpolate linearly. A zero to zero curve will again lead to zero density, which is no smoke in the render.

2) You solve the prolbem using image planes and compositing

The pyro shader comes with serveral image-planes already built in for you. The only downside is, this is not documented You have to know that they exist. Go to the shop-Network and dive into the pyro shaders network. There you will see some export parameters which are your preexisting available image planes. You have: fire mask, fire, smoke mask, smoke. Fire and smoke are type vector image planes (color information), and the masks are type float image planes (black and white information). Now all you need to know is the name of the vex-variable to use in the render node in order to output the imageplanes for the fire. Here is an example what that will give you (forget about the odd colors, in the video, he just colored the black and white mask passes) vimeo.com/38406595#at=0 When you rendered out your sim, you can use the mask passes in compositing to just get the information what you want (cutting away all the rest = smoke). Advantage: If you decide that you afterall need the smoke, you have it (just need to blend it in / unmask it)

Check my screenshots for further information.

I hope that helps! Pyro is one of the most complex topics I encountered learning Houdini. All the best to you!

EDIT: I found something in addition. When you go to the pyro shelf, there is a "smokeless fire" button. Create a sim using this shelf tool. You will see in the pyro solver that "emit smoke" is turned off, and that they (in the shader) use the heat-field for density-shading instead of density. This works as well!

Edited October 15, 2012 by Scratch