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7.1.3 *hidden*

scatter_secondary_anisotropy

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A phase function model with a mixture of two "Henyey-Greenstein" lobes. This provides a more realistic approximation to the physical phase function of scattering media such as clouds.

scatter_secondary_anisotropy_mix

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Controls the weight for scatter_secondary_anisotropy (0-1).

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The cloud on the left (anisotropy 0.5) generates a "silver lining" at the rim of strongly forward scattered light from the sun behind. The cloud on the right (anisotropy -0.3, mix weight 0.5) fills in the bulk of the cloud with back-scattered light while maintaining the silver lining.


The image below shows the full parameter space of the dual-phase function model (each cell shows the phase function shape for a given combination of lobe anisotropies, which varies as the lobe mix weight is animated). The blue curves correspond to the old single lobe model.

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emission_scaling

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This mode is most useful when mixing different types of volumes with varying scattering properties. It supports the scaling of volumetric emission in a more physically correct manner.

  • Opacity: emission scaling mode is based on density and transparency and scaled appropriately to the opacity of the resulting volume. This is physically accurate for blackbody if the scattering color is black.
  • Thermodynamic: emission scaling mode is the most physically correct as it also takes into account scattering color, since according to thermodynamics volumes with higher scattering albedo emit less blackbody radiation. For example, burning hydrogen produces steam but barely emits blackbody radiation while sooty smoke readily does.
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blackbody_intensity

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The blackbody_intensity control can be dialed above 1 for convenience.

blackbody_contrast

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The blackbody_contrast parameter (non-physically) reduces the brightness difference between parts of the volume at different temperatures, which can be useful for artistic purposes.  It reduces the disparity in brightness between parts of the volume at different temperatures, which tends to bring out the blackbody colors more vividly (though note that only value 1 is physically correct).

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