Method

The Pathtracer node simulates lighting of solid objects accurately with support for multiple bounces of specular and diffuse reflections and refractions with varying roughness and other material attributes.
This is achieved by casting lots and lots of rays, randomly distributed, and accumulating the results. The sum of all the random rays ends up with a smooth, converged image over time.
As such this node can be very slow and is not intended for real-time use.

Typically, only a very small number of rays per pixel can be cast per frame at real-time rates – but to produce a converged image, hundreds or thousands of rays must be accumulated per pixel. It is possible to use the “Samples” parameter to control how many rays are cast per pixel per frame at the cost of longer frame times. However, the more common solution is to use continuous refinement. This casts few or even only one ray per pixel per frame, varying that ray randomly each time and averaging the result, so the image converges from noisy to smooth. When anything in the scene changes or animation occurs, refinement resets. This allows you to work on your scene using a fast but noisy render as you edit it; then leave it to refine for a few seconds to see how it looks when converged.

A ray may be one of several types: diffuse, glossy (specular) or refraction. A ray is initially spawned from a surface based on the material and importance: a metallic surface will mainly spawn glossy rays, a flat diffuse surface will mainly spawn diffuse rays and so on. When a ray hits another surface and bounces, it may change type. The number of bounces is limited per ray type. Typically diffuse samples become less visible quickly through multiple bounces.

Attributes

Name Description
Denoiser Shader Loads denoiser shader.
Path Trace Shader Loads path trace shader.
Ray Generation Shader Loads ray generation shader.
Max. Diffuse Depth The maximum number of diffuse bounces per ray.
Max. Glossy Depth The maximum number of glossy bounces per ray.
Max. Refraction Depth The maximum number of refraction bounces per ray.
Ray Bias Biases the ray start position away from the spawning surface – to reduce fighting artefacts in exchange for less accuracy.
Sample Clamp The maximum brightness allowed for a given ray.
Diffuse Bounce Multiplier Change how effective the bounced rays are.
Kill Caustic Paths Turns of ray caustics from transparent objects.

Visualisation

Name Description
Show BVH (Debug View) Pathtracer rays are tested against box bounding box on each object and then geometry after that if its a hit.

Inputs

Name Description Typical Node Input
Object Nodes Only nodes input will be used for pathtraced. 3D Object
Field Allow a field to be refracted by the glass Field Root
Transform Modifier Links all transform properties to the input node. Null
Target Node Always faces the x-axis towards the inputs anchor point. Null
Local Transform Override Override the transformation values of the node, relative to its parent. Null

Outputs

All nodes connected to this node are treated as if flowing to the parent node, and inherits any transformation changes along the chain.