mental ray Architectural and Design Visualization Shader Library

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54 2 Architectural MaterialFor lemonade in a glass, imagine a ray of light travelling through the air (IOR = 1.0) enterthe glass, and is refracted by the IOR of the glass (1.5). After travelling through the glass theray leaves the glass and enters the liquid, i.e. it passes an interface from one medium of IOR1.5 to another medium of IOR 1.33.One way to model this in computer graphics is to make the glass one separate closed surface,with the normals pointing towards the inside of the glass and an IOR of 1.5, and a second,closed surface for the beverage, with the normals pointing inwards and an IOR of 1.33, andleaving a small “air gap” between the container and the liquid.While this “works”, there is one problem with this approach: When light goes from a higherIOR to a lower there is a chance of an effect known as “Total Internal Reflection” (TIR). Thisis the effect one sees when diving in a swimming pool and looking up - the objects above thesurface can only be seen in a small circle straight above, anything below a certain angle onlyshows a reflection of the pool and things below the surface. The larger the difference in theIOR of the two media, the larger is the chance of TIR.So in our example, as the ray goes from glass (IOR=1.5) to air, there is a large chance of TIR.But in reality the ray would move from a medium of IOR=1.5 to one of IOR=1.33, which isa much smaller step with a much smaller chance of TIR. This will look different:Correct refraction (left) vs. the “air gap” method (right)The result on the left is the correct result, but how it is obtained?The solution to the problem is to rethink the modeling, and not think in terms of media,but in terms of interfaces. In our example, we have three different interfaces, where we canconsider the IOR as the ratio between the IOR’s of the outside and inside media:• Air-Glass interface (IOR = 1.5/1.0 = 1.5)• Air-Liquid interface (IOR = 1.33/1.0 = 1.33)
2.6 Tips and Tricks 55• Glass-Liquid interface (IOR=1.33/1.5=0.8)It is evident that in the most common case of an interface with air, the IOR to use is theIOR of the media (since the IOR of air is 1.0), whereas in an interface between two differentmedia, the situation is different.To correctly model this scenario, we then need three surfaces, each with a separatemia material applied:The three interfaces for a liquid in a glass• The Air-glass surface (blue), with normals pointing out of the glass, covering the areawhere air directly touches the glass, having an IOR of 1.5• The Air-liquid surface (green), with normals pointing out of the liquid, covering thearea where air directly touches the liquid, having an IOR of 1.33• The Glass-liquid surface (red), with normals pointing out of the liquid, covering thearea where the glass touches the liquid, having an IOR of 0.8By setting a suitable refr falloff dist and refr falloff color for the two liquid materials (toget a colored liquid), the image on the left in the comparison above is the result.2.6.2.7 The Ocean and Water SurfacesA water surface is a slightly different matter than a visibly transparent liquid.The ocean isn’t blue - it is reflective. Not much of the light that goes down under the surfaceof the ocean gets anywhere of interest. A little bit of it is scattered back up again doing alittle bit of very literal “sub surface scattering”.To make an ocean surface with the mia material do the following steps:
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mental ray Architectural and Design
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Table of Contents1 Introduction 11.
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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 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: 2.6 Tips and Tricks 53There is one
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
Page 96 and 97: 90 4 Camera- and Exposure Effects4.
Page 98 and 99: 92 4 Camera- and Exposure Effects1,
Page 100 and 101: 94 4 Camera- and Exposure EffectsTh
Page 102 and 103: 96 4 Camera- and Exposure Effectscr
Page 104 and 105: 98 4 Camera- and Exposure EffectsEv
Page 106 and 107: 100 4 Camera- and Exposure EffectsS
Page 109 and 110: Chapter 5General Utility Shaders5.1
Page 111 and 112:
5.2 Environment Blur 105replaced by
Page 113 and 114:
5.2 Environment Blur 107But what is
Page 115 and 116:
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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