Hi there

I have a setup with a fire simulation and have added a volume light to emit light from the resulting geometry.

It does work fine so far, although I have not found out how to control the intensity of the emission. As far as I have understood from the docs, the intensity is driven by the emission from the pyro object, but i'm not sure exactly which parameter is meant by that…

Any ideas?

Regards,
michael

Assuming you used the Volume Light shelf tool along with the pyro shelf tools to set things up, there are two areas where you can control the emission of the light from the pyro object containing the various fields:

The Pyro Shader's Emit Brightness parameter
or
The Volume Light's Intensity parameter

Use the Volume Light Intensity parameter as it doesn't force you to re-calculate the point cloud if you wish to cache these to disk or if using ipr and not working with invalid point clouds causing you to hit the Render button to rewrite the point cloud each time you tweak the Emit Brightness on the Pyro shader (or any emission control affecting Ce export).

—-

The Volume Light set up from the shelf (which is just a standard Houdini Light object) when you select the import_pyro _build object is set up to generate a point cloud from the input geometry (the density volume which is the smoke to be lit among other objects) when you hit render.

The Volume Light Shelf Tool also sets the shader path on the light object set up to geometry rendering (H12.5) to the Pyro shader itself. This means that if that shader exports to a vector colour variable called “Ce” for Colour emission then this will be used to determine the colour of the light which the Pyro shader certainly does. The value written to Ce is multiplied by Emit Brightness giving you a control over the emission intensity.

The Pyro shader sets the fire component to the vector export “Ce” so that the fire is used to colour the scattered points which in turn cause the geometry light to emit this light.

Wrapping things back up to the beginning, it now makes sense that you can control the emission intensity either by reducing the Ce export and re-calculating the point cloud with that Ce emission colour value or you simply change the intensity of the Light object set up to generate the point cloud referencing the Pyro material.

Hope this helps.

Hi Jeff

First of all, many thanks for the elaborate reply. It did help.

I found that only the “Emit Brightness” parameter of the shader had an effect on the brightness of the emitted light.

Changing “Light Intensity” did not have any visible effect (I tried values from 1 to 5000). Does this work differently for you?

Also, I have taken a look at the shader network and found the Ce attribute, but I'm not yet sure how to tweak that.

Best regards,
michael

Works for me.

I just run a pyro sim, select the Volume Light from the Light and Cam shelf, select the object with the volumes fetched from the sim and referenced to the Pyro shader.

This creates a new Houdini Light set up as a geometry type, referencing the object with the volumes and if that object has a shader assigned to it, also references this shader in to the Material field.

Now you can control the brightness either from the Pyro shader or the light brightness.

—-

A Parameter VOP with the Export flag set is used to export a variable called Ce which is the standard Color emission variable name. To change it, you need to change the data wired in to it. For example you can insert a Multiply VOP and wire in your own Parameter to scale the Ce export up or down.

See the attached file.

Hi Jeff

Thanks a bunch again - will have a go with your tips in the next few days.

Best regards,
Michael

Hi Jeff

Thanks a bunch again - will have a go with your tips in the next few days.

Best regards,
Michael