10/4/2023 0 Comments Translucent objects![]() Very large self-shadowing particle systems will get reduced shadowmap resolution, since the shadowmap is stretched to cover the system bounds. The easiest way to set this up is to author your particle movement, then right-click on the 'show bounds' button on the Cascade toolbar, which will pop up a dialog that allows you to generate fixed bounds. Translucent self-shadowing uses per-object shadows, which means that it needs user specified fixed particle system bounds and they need to be correct. Directional lights also have subsurface shading for lit materials using the subsurface shading model. Directional lights however do translucent self shadowing per-pixel, and get much higher quality. ![]() Translucency self shadowing goes through the lighting volume for point and spot lights, so it is often not visible due to low resolution unless the effect is very large and dense. This is implemented with Fourier Opacity maps, which do a great job for shadowing from blobby volumes, but have severe ringing artifacts with more opaque translucent surfaces. ![]() Translucency can cast shadows onto the opaque world and onto itself and other lit translucency Actors. Volumetric effects Casting Shadows & Self-Shadowing The left sphere is lit translucency using the Indirect Lighting Cache, the right sphere is opaque with baked lighting from Lightmass. The indirect lighting interpolates over time if the bounds center changes, so it does not pop. There is only one sample taken for the whole object, even if it is a large particle system. Only one lighting sample is interpolated, at the center of the object's bounds. Translucent materials receive diffuse GI from the Indirect Lighting Cache. Light functions are also taken into account. Shadowed direct lighting from all movable light types is injected into the translucency lighting volume. Raising this increases lighting volume coverage but reduces effective resolution. R.TranslucencyLightingVolumeOuterDistance, which defaults to 5000. R.TranslucencyLightingVolumeInnerDistance, which defaults to 1500. Raising this by a factor of 2 increases the cost to light volume by a factor of 8. R.TranslucencyLightingVolumeDim, which defaults to 64. The volume is configured through cvars that can be set differently based on the scalability level: This allows lighting to be known in a single forward pass for any point inside the volumes, but has the downside that the volume texture is fairly low resolution, and can only cover a limited depth range from the viewer. Lit translucency gets most of its lighting through a series of cascaded volume textures oriented around the view frustum. Different lighting techniques are needed for each of these, so a material must specify the Translucency Lighting Mode that should be used. Translucent effects generally fall into a few categories: volumetric, volumetric but dense enough to have normal information, and surfaces.
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