mental ray Architectural and Design Visualization Shader Library

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42 2 Architectural Material2.5.10.3 The new behavior of refractions added in mental ray 3.8In mental ray 3.8 the behavior of running out of the refractive trace depth has changed.Prior to version 3.9, running out of refractive trace depth would return a black refraction.Most other transparency/glass shaders return the environment, which can create very oddresults when rendering an indoor rendering with an extremely bright outdoor environment,and bright areas appear in glass objects in dark cupboards that suddenly refract some sky.But returning black, as was done in previous versions, while less damaging, isn’t the idealchoice either. One does not want to see large swatches of black suddenly pop up in a glassinstallation. Having to manually tune trace depth is cumbersome and error prone.Ideally, one wants the glass to always refract its surroundings, no matter what, leaving thechoice of how deep to trace to the renderer.Trace depth limits like refl depth exist to prohibit rays from bouncing indefinitely to createlarge render times. But only rays that change direction (such as reflections and refractions) canbounce around indefinitely - straight (transparency) rays cannot. These rays will eventuallyeither escape the scene, or hit an opaque object. And the mia material utilises importancepropagation, which will automatically cull any rays whos contribution to the final pixel goesthe refl cutoff value.For these reason, the mia material in mental ray 3.8 will willingly and by design ignorerefractive trace depth, and will not stop tracing rays when the refractive trade depth is reache.Instead, it will switch from refractive rays to plain straight transparency rays. Since these raysare guaranteed to escape the object (as mentioned above), they will always return a reasonablecolor for deep refractions, be it the sky, or a surrounding opaque object.The new behavior relieves the user from having to think about refractive trace depth - deeprefractions will always look reasonable, even though perhaps not technically correct.If the old behavior (returning black) is required, setting refl depth to -1 will switch it backon. Rays that hit the scene global refractive trace depth will then be black.
2.5 Detailed Description of Material Parameters 43The new refractive trace depth behaviorThe above figure shows in the first row the result of using a legacy shader - Dielectric - (whichreturned the environment, and hence did not look correct indoors), in the second row the premental ray 3.8 mia material (which returned black, and hence did not look correct outdoors)and in the third row the new mia material which looks correct in both cases.
Page 1 and 2: mental ray Architectural and Design
Page 3 and 4: Table of Contents1 Introduction 11.
Page 5: Table of Contentsix3.8.3 Examples .
Page 9 and 10: Chapter 2Architectural Material2.1
Page 11 and 12: 2.2 Fundamentals 52.2.1.1 A Note on
Page 13 and 14: 2.3 Features 7Hence, when using GI:
Page 15 and 16: 2.3 Features 9The rules are as foll
Page 17 and 18: 2.3 Features 11In the real world
Page 19 and 20: 2.3 Features 13Used alone, an AO sh
Page 21 and 22: 2.3 Features 152.3.7 Performance Fe
Page 23 and 24: 2.4 Quick Guide to the Material Par
Page 25 and 26: 2.5 Detailed Description of Materia
Page 47: 2.5 Detailed Description of Materia
Page 55 and 56: 2.6 Tips and Tricks 49• For extre
Page 57 and 58: 2.6 Tips and Tricks 51Diagram for g
Page 59 and 60: 2.6 Tips and Tricks 53There is one
Page 61 and 62: 2.6 Tips and Tricks 55• Glass-Liq
Page 63 and 64: 2.6 Tips and Tricks 57Enjoy the tro
Page 65 and 66: 2.6 Tips and Tricks 59Many small ad
Page 67 and 68: Chapter 3Sun and Sky3.1 Introductio
Page 69 and 70: 3.4 Common Parameters 633.3 Importa
Page 71 and 72: 3.5 Sun Parameters 65• saturation
Page 73 and 74: 3.6 Sky Parameters 67light"sun",# T
Page 75 and 76: 3.6 Sky Parameters 69• sun direct
Page 77 and 78: 3.8 Sky- and Environment Portals 71
Page 89 and 90: 3.9 Photometric Lights 833.9 Photom
Page 91: 3.9 Photometric Lights 85• When i
Page 94 and 95: 88 4 Camera- and Exposure EffectsAl
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92 4 Camera- and Exposure Effects1,
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94 4 Camera- and Exposure EffectsTh
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96 4 Camera- and Exposure Effectscr
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98 4 Camera- and Exposure EffectsEv
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100 4 Camera- and Exposure EffectsS
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Chapter 5General Utility Shaders5.1
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5.2 Environment Blur 105replaced by
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5.2 Environment Blur 107But what is
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5.2 Environment Blur 109Glossiness
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5.3 Light Surface 111An example of
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5.3 Light Surface 113the other two
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5.3 Light Surface 115Complex geomet
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5.3 Light Surface 117Another exampl
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mental ray Architectural and Design Visualization Shader Library

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