There is however one case where letting the direct light simply pass through the object can both look correct and save a lot of calculations, and that is when the object is a thin surface with consistent thickness like window glazing. if we tell the render-engine to just let direct light pass through the object we won’t get a correct realistic result, even if the light gets colored by the object’s transparency color. light is refracted through them, gets focused in some areas of their surroundings ( caustics) but can’t pass through them directly, so a shadow is created.Ī good example of this would be a glass ball, acting like a lens, focusing the light into a tiny area, and otherwise having a regular elliptical shadow. they don’t block light, they change its direction. It’s a common intuitive mistake, that transparent objects don’t cast shadows, but they actually do. Lensing, caustics and transparent shadows: Note that while for the monkey statue, the fast flat transparency settings produce an unrealistic result, the window glazing model loses very little of its look with the flat fast settings: In the comparison images below (rendered with Cycles), the images on the left were rendered with physically correct glass settings, 8192 samples + denoising,Īnd the images on the right were rendered with “flat” transparency settings and 1024 samples + denoising. In this short article we’ll cover the different methods for rendering transparency effects, the reasoning behind them and the way to configure these settings in different render-engines. However, for thin surfaces of even thickness, like window glazing and car windshields, these optical effects can be rendered in much cheaper (non physical) methods, with very little compromise on final image quality or look, and even have an easier setup in most cases.įor this reason most popular render engines have object (mesh) and material (shader) parameters that allow configuration of the way these transparency effects will be rendered.
In theory, all clear* refractive surfaces should have their shadow calculated using a refractive caustics calculation in-order to render the refractive lensing** effect correctly, have their transparency color calculated as volumetric absorption of light through the medium in-order to render the color correctly for areas of different thickness, and have not only external reflections, but also internal reflections calculated, in-order to render the interaction between light and the transparent body correctly.
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