Houdini 20.5 Nodes Shader nodes

Mantra: Houdini Engine Procedural shader node

Invokes Houdini Engine for each point on the object’s geometry and instances the geometry output by the script at that point.

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Since 13.5

Overview

This shader lets you specify a SOP asset to generate instanced geometry at render time. For each point in the object this shader is applied to, mantra copies any point attributes onto identically named parameters on the SOP, and then cooks the SOP to generate the instanced geometry.

For example, you could set the shader to use the Platonic SOP, and add a point attribute named type on the source object. The point attribute will control which platonic solid is generated (since the Platonic node has a parameter with the internal name type which controls the type of solid).

Warning

To render a scene using this shader, you must start mantra using the -e basic|full command line option. See the help for -e.

Notes

  • If you don’t specify the bounding box, the shader uses the bounding box of this object’s geometry, increased by the predicted instance sizes.

  • If the SOP contains a SHOP network with SHOPs that are used, a non-displayed version of the SOP should be in your scene file. You should also set the output driver to have the SHOP References parameter set to Declare all SHOPS.

  • The procedural shader will pass its level of detail to a parameter named lod. If there is an attribute named lod, it will override the level of detail calculated by mantra.

Parameters

Main

SOP

Name of the SOP type. This is the name, not the label. Examples: box, platonic, sphere.

OTL Files

Filenames with paths of OTL libraries that hscript should otload prior to creating the SOP.

Basic Size

The estimated maximum size (as a radius in each direction) of each instance. Mantra uses this to compute the new bounding box for the object after instancing. If you underestimate how much space to add for the instances you can get rendering errors, while overestimating might slow the render down, so it’s better to overestimate.

Orient to Point

If turned on, it will try to orient to the points velocity, etc. Even if not set, a translation to the point’s space will be performed.

Defer Geometry Creation

Normally the procedural will generate all geometry when the procedural is rendered. This option defers creation of instances until each instance is rendered. For example, if you have scattered instances, but only render a few of them, this option may save memory since some geometry will never be created.

By deferring geometry creation, the engine procedural can no longer share geometry between different point instances.

SOP HDA Requires LOD

The engine procedural is able to compute an approximate level of detail and pass this to the SOP HDA using a parameter named lod. If the SOP HDA doesn’t cook differently for different levels of detail the engine procedural is able to be more efficient.

IFD Bounds

Bounding Box

The bounding box controls let you specify a bounding box for the referenced geometry. Only when this bounding box is “on screen” will mantra load the referenced geometry. You can set Bounding box to No bounding box required, in which case mantra will always load the references geometry regardless. You can also specify the bounding box by referencing the SOP’s bounding box in the SOP Bounds parameter.

SOP Bounds

The geometry whose bounding box you want to reference.

Min Bounds

The minimum bounding box dimensions, when setting explicit bounds.

Max Bounds

The maximum bounding box dimensions, when setting explicit bounds.

Shader nodes