Houdini 20.0 Shelf tools

Simple Fireball shelf tool

Creates a large rising and expanding explosion.

On this page
Pyro simulation in the viewport. Color space: ACES, Voxels Size: 0.05.
Pyro simulation rendered with Karma. Color space: ACES, Voxels Size: 0.05.


The videos above are color-corrected and use OCIO/ACES. You can read more about working with color spaces in Houdini on the Color management in Houdini page.


This shelf tool sets up a sparse pyro simulation of a medium-size explosion. Rather than building a DOP network, it uses the SOP-level tools to build a simple network to work with sparse pyro.

The explosion consists of an initial blast, followed by a rising fireball. As long as there are sufficient reactants (corresponding to the emissive flame field), the fireball will continuously emit soot and heat and continue to expand. These various outputs, as well as the time it takes the fireball to burn up, are controlled through parameters on the Flames tab of the Pyro Solver.

Using Simple Fireball

  1. Click the Simple Fireball tool on the Simple FX tab.

  2. Select the location of the fireball in the viewport.

Understanding Simple Fireball

  • If you have a Houdini FX License, you can dive inside the solver and edit the subnet with custom DOP forces. Otherwise, you can stay at the SOP level and use the exposed parameters on the node.

  • create_burn sets up the temperature and burn sources. Burn gets merged with the pyro flame field (to refresh the available reactants) and the divergence field (causing the initial outward explosion). Rates of the sourced values are animated through the Scale parameters of the Pyro Source node.

  • The shape of the base is determined by the geometry of the starting node in the chain, which is a sphere by default.

  • The parameters on the Pyro Solver SOP have the greatest influence on the motion and emergent shape of the fireball and its smoke.

  • If you dive inside the Pyro Bake Volume node, you can use the following controls on the Pyro Shader to do the following.

    To...Do this

    Change the color of the smoke based on density

    1. Change the menu next to Smoke Color from Constant to Use Ramp.

    2. Set the Density Range parameter to control the color of the smoke at given density values.

    3. Set the Smoke Color Ramp to change the color of the smoke based on Density Range.

    Change the color of the smoke based on how light scatters through the volume

    Change the Absorption Color. The value of 0.425 (red),0.36(green), 0.3(blue) could be a good starting point for more realistic looking smoke.

    Scale smoke density using an other volume

    1. Turn on the Use Control Volume checkbox.

    2. Set Density Control Volume on the Bindings tabs to the field that you want to use to affect the density. Usually temperature or flame are good choices for this purpose.


You can download a fully configured, production ready version of this shelf tool from the SideFX Content Library.

Shelf tools

Using the shelf

  • Customize the shelf

    How to change the look of the shelf, change and rearrange its contents, and create your own shelf tools.