mental ray Architectural and Design Visualization Shader Library

106 5 General Utility ShadersIt is important to remember that mia envblur does a one time rasterization of theenvironment shader at start up time. This means that that shader must be constant acrossthe scene, and cannot be a complicated position-dependent blend of environment shaders. Theenvironment can still change over time, since the rasterization step is performed anew eachframe.5.2.2 Use CasesThe environment blur shader mia envblur is intended to increase quality and performance ofrenderings that are largely reflecting the mental ray environment (i.e. that do not primarilyreflect other objects).The shader is primarily useful in product visualization renderings that are surrounded by anHDRI environment map for reflections, and also for visual effects work where one wants tohelp integrate CG objects in a real scene with the help of HDRI reflections, and want a smoothyet fast lookup.The shader is not as useful for interior architectural renderings, since in those (enclosed)scenes, most reflection rays are bound to hit other objects; the purpose of this shader is tohelp reflection rays that do not hit other objects, i.e. the largest benefit is in an “open” scene 1 .Object reflecting an environment mapHere an example object is reflecting an environment map 2 with no glossiness (i.e. perfectmirror reflection). This looks fine, because there is no quasi-random sampling performed.1 It is also very useful combined with using refl falloff dist in mia material.2 The “Galileo’s tomb” probe from www.debevec.org, which contains many small bright areas that tend tobe troublesome in this context.