Piecewise volumetric path tracer (volpath)

Parameter	Type	Description	Flags
max_depth	integer	Specifies the longest path depth in the generated output image (where -1 corresponds to \(\infty\)). A value of 1 will only render directly visible light sources. 2 will lead to single-bounce (direct-only) illumination, and so on. (Default: -1)
rr_depth	integer	Specifies the minimum path depth, after which the implementation will start to use the russian roulette path termination criterion. (Default: 5)
hide_emitters	boolean	Hide directly visible emitters. (Default: no, i.e. false)

This plugin provides a piecewise volumetric path tracer that can be used to compute approximate solutions of the radiative transfer equation for plane parallel geometry. Its implementation makes use of multiple importance sampling to combine BSDF and phase function sampling with direct illumination sampling strategies. On surfaces, it behaves exactly like the standard path tracer.

This integrator only works with piecewise media. It uses assumptions on the medium’s geometry to accelerate the sampling and transmission calculations.

This integrator has special support for index-matched transmission events (i.e. surface scattering events that do not change the direction of light). As a consequence, participating media enclosed by a stencil shape are rendered considerably more efficiently when this shape has a null or thin dielectric BSDF assigned to it (as compared to, say, a dielectric or roughdielectric BSDF).

Note

This integrator does not implement good sampling strategies to render participating media with a spectrally varying extinction coefficient. For these cases, it is better to use the more advanced volumetric path tracer with spectral MIS, which will produce in a significantly less noisy rendered image.

Warning

This integrator does not support forward-mode differentiation.