Bi-directional Path Tracing


Bi-directional Path Tracing

Bi-directional path tracing traces eye and light paths independently and connects the subpaths. This gives a number of different ways to construct the same path. Weighting (cfr. E. Veach, Siggraph 95) ensures an unbiased (and good) solution. Good for caustics and strong indirect light. The use of regular expressions gives a flexible framework for dissecting parts of the light transport  (good for didactical purposes and advanced multi-pass methods...)


Bi-directional Path Tracing Control Panel


Pixel Sampling

Path Length Configuration

These options control lengths of eye-and light paths separately, which can be used to choose different algorithms. The names of the options speak for themselves. Path length is the number of segments (rays) in a path.

Maximum combined path length: controls the number of interreflections. Connections between eye and light sub-paths will never result in a path longer than specified  here.

Example uses (see also presets):

Max Eye Path: 7
Max Light Path: 7   => Real bidirectional path tracing

Max Eye Path: 7
Max Light Path: 1   => Path tracing with direct light sampling

Max Eye Path: 7
Max Light Path: 0   => Path tracing without direct light sampling (You don't want to do that...)

Max Eye Path: 1
Max Light Path: 7   => Light or particle tracing with direct connection to the eye (cfr Ph. Dutre Ph.D.)

Max Eye Path: 0
Max Light Path: 7   => Not possible, this image would be black as we use a point camera.

Light source importance sampling:

Use an importance criterion to compute (some) direct light (eye sub-path connected with single light point) (cfr. stochastic ray tracing). If not on, power based sampling is used.

Regular Expressions

Regular expressions allow you to compute only some parts of the light transport. The part to be computed is specified by a simple regular expression. Each path is evaluated taking into account the expressions.

A precomputed radiosity solution can also be incorporated when using regular expressions. Note that currently ONLY THE GALERKIN
method can be used for this.

Presets (see below) allow to set expressions for some useful cases.

Options:

Regular expression syntax

Presets

Some presets are provided to set options for some interesting cases. Most preset names are self-explanatory. See Frank Suykens, 'Combining Bi-directional Path Tracing with Multi-pass Rendering', WSCG '99 for more information or 'Weighted Multi-pass Methods', Eurographics '99 for some interesting extensions of this framework. These paper are available online on our publications web page.
 

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Last update: October 31, 2000