To render particles in Arnold for Houdini, Geometry Properties must be added on an OBJ containing points or particles. The properties relevant to point rendering are on the Shapes tab. Particles can be rendered as disks, spheres, quads or volumes.

SSS will not work with particles (it is currently only supported for polymeshes). This is due to be fixed in a future release.

Particles As Surfaces

When rendered as disks, spheres or quads, you can set the default radius of the particles. 

For quads, you can also set the default aspect ratio and rotation.

Particles As Volumes

When the Volume Step Size is set to a value above 0, the particle will be rendered as constant density volume spheres. You also need to connect a volume shader to OBJ to render properly. 



The radius of the particle will become a sphere filled with density.

Particle Attributes

Radius, Scale and Rotation properties can be overridden with attributes to provide more control or randomization of particles.

For example, use an attribcreate node (Tab > Attribute > AttribCreate) to create the attributes.

 

You can use the following float point attributes to set per particle parameters. Both Arnold and Houdini names can be used but Arnold takes priority if both are present.

 Arnold Houdini
ar_radiuspscale 
ar_rotation spriterot 
ar_aspectspritescale* 

spritescale is a float[3] vector attribute, whereas ar_aspect which is just a float attribute.

Points rendered as Quads with random radius, rotation, and aspect