Realistic cloud with Phase Function 體積雲著色器

 

V-Ray's VRayVolumeGrid allows you to load AUR or VDB files as volumetric data. However, proper shading settings are essential for achieving realistic cloud appearance and natural light scattering.

In the Smoke Color rollout of VRayVolumeGrid, you can find the Phase Function parameter, which controls how light scatters as it travels through the volume. To enable the Phase Function, set Scattering to Ray-traced.

Let’s consider two scenarios. First, a front-lit setup, where the camera and the sun are positioned on the same side of the volume. As you can see, setting the Phase Function to a positive value of 0.7 (Forward Scattering) produces the most realistic result. The default value, 0.0 (Isotropic Scattering), also produces a reasonable result in this setup. However, a Phase Function of -0.7 (Backward Scattering) makes the volume appear unrealistically dense and overly thick.

Here is the second scenario: backlighting, where the light source is positioned behind the volume relative to the camera. Again, a positive value, which produces forward scattering, gives the most realistic result. In contrast, -0.7 produces stronger backscattering, making the clouds appear overly dense and unrealistic.

The diagram also suggests that, in a front-lit setup, positive values can render faster than negative ones. It also shows that the front-lit setup renders faster than the back-lit setup.

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