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You will noticed I have dropped the "Division Size" down and I have upped the "Size" of the simulation to 30 x 40 x 30. Change the Density Scale to 1 and Shadow Scale 1 in the Multi tab. I have also added a stock gasrepeatsolver node after the source_fuel_from_torus node to give the flame an extra boost. Set Minimum Pass to 1. Turn on Override Minimum with Data.
Finally I made a few modifications to the pyrosolver node as noted below:
You can increase the smoke amount Smoke Amount from 1 to 3 if you want the simulation to have more smoke.
One of the quick and easy steps for setting up RenderMan for use in Houdini is to use the RenderMan RIS shelf buttons. I next pressed the "RIS ROP" button on the shelf and that gives me a ROP (Render OPerator) and also places down a default path tracer intergrator and creates an RIS specific SHOP (RIS SHading OPerator network).
In order to help me gauge my lighting, I decided to drop a shiny sphere in scene for reference. I clicked in the scene view and hit TAB and typed "Sphere" to drop a sphere in the scene off to the left of the fireball. I then clicked into the "risnet1" SHOP network and hit tab and types "PxrDisney" to create a pxrdisney BXDF. I modified the paramaters of the PxrDisney shader to make it a shiny mirror ball as shown below:
To also give some nice shadows on the smoke of the fireball, I add a "Rect Light" (using the shelf button) off the the left side of the fireball. The parameters are as show below. Note I scaled the light up uniformly by a factor of 10.
We finally color correct the final values coming out of the pxrblend1 node and feed that into the Emit Color on the PxrVolume shader. Note we first change the exposure: Exposure to 5.
And we also alter the output range: Output Range.
We don't show a screen shot, but on the PxrVolume node, we set the Max Density parameter to 20, to give RenderMan hints that will help it converge faster. We also switched over to the sampling tab, and set Samples to 8 and set the Step Size to 0.1
Set the pyro_import's Material to /shop/risnet1/pxrvolume1 to assign the volume shader.
At this point, the scene can finally be rendered out. One can add a camera object by clicking on the Scene View, hitting TAB and typing "Camera". The cam1 node can then be selected with the yellow drop down in the upper right hand corner of the Scene View. By clicking the padlock icon, next to the camera selection menu, the camera can be interactively manipulated to frame the scene for rendering.
Once the camera has been setup, we can switch to the "Render View". There one can select the ris1 ROP and the cam1 camera, and hit the render button. Depending on how far along the volume simulation has advanced, Houdini will take some time generating the scene data before it starts to render, but eventually rendered buckets will start to appear and will continue to refine until the render is finished. It should converge fairly quickly like below.
Then we will select the "Gear Icon" next to the "Houdini H" icon. This icon will let us add new user interface elements to the RIS ROP node.
One the "Edit Rendering Parameters" has been selected, type "Sample Filter" in the Filter entry box in the lower left hand corner, then select "Pixar's RenderMan 21.0" and open up the Shaders section. Select both the "Display/Sample Filter" and the "Use Sample Filter" UI elements and DRAG them over to the Existing Parameters section of the RIS tab.
Now when rendering the volume, it will not look blown out, and the contrast in the explosion will look more appealing.