Houdini 20.5 Mantra materials

RIS

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Overview

RenderMan’s RIS is a rendering mode designed for efficient global illumination. You can use this mode by turning on the RIS Mode checkbox on the RenderMan node.

This rendering mode utilizes BxDF shaders, which are implemented as C++ plugins. They are represented in Houdini as digital asset nodes that can be placed inside the RIS shading network. In addition to BxDF shaders, which are assigned to geometry (much like surface shaders), there are also integrator shaders that can be referenced in the Integrator parameter of the RenderMan node. There are also various pattern and utility shaders that serve as inputs to the BxDF shaders for dynamic calculation of the main shader parameters, and to create shading groups and layers.

In addition to RIS shaders, the RIS shading network also allows OSL shaders. The OSL shader can be defined with an OSL shader node or, if it’s compiled as .oso file, with a digital asset, similar to RIS shaders. The only difference is the Render Mask that should be set to OSL for OSL shaders (and RIB for RIS shaders). OSL shaders are used the same way as RIS pattern shaders.

For more information about RIS, please refer to the RenderMan for Houdini (RfH) or RenderMan Wiki documentation.

How to

To...Do this

Define a new BxDF, integrator, or a pattern shader node for a corresponding custom C++ plugin

  1. In the main menu, choose File ▸ New Operator Type…

  2. Specify the name and label for the new node type.

  3. Choose VEX Builder Type as the operator style, and Accept.

  4. In the properties dialog that pops up, go to the Input/Output tab and turn on the External or Procedural Shader.

  5. In the Node tab, specify the C++ plugin name as Shader Name.

  6. Choose an appropriate Shader Type from the drop down menu (eg, BSDF Shader).

  7. Specify RIB as Render Mask for the shader to be available to RenderMan .

  8. Specify risnet as VopNet Mask for the node to appear in the Tab menu inside the RIS shading network.

    Tip

    Click Apply for the render mask to get committed, so that the parameters show the RMan Type option in the next step.

  9. In Parameters tab define shader’s parameters. Be sure to specify RMan Type as well.

  10. In the Input/Output optionally define inputs and outputs.

    You can click Create Inputs from Parameters to automatically generate the inputs.

Create an OSL shader

  1. In RIS shading network press Tab to open Tab menu and create OSL Shader.

  2. Dive inside the OSL shader and define the its logic.

  3. Use Parameter VOP to define shader input parameter.

  4. Set Export parameter on the Parameter VOP to When Input is Connected to make it an input-output shader parameter.

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