CS 468 Cg Texture Mapping

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CS 468Cg Texture Mapping

• Jon Moon
• Spring 2004
• Computer Science
• Cornell University

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Agenda

• NVIDIAs Cg Browser effects
• Bump Mapping
• Reflection Mapping
• Thin Film
• Bump Horizon Mapping
• Car Paint
• Bumpy Shiny Patch
• Watch demo, understand the shaders

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Cg Commands

• saturate(x) same as clamp(x,0,1)
• lerp(a,b,f) (1-f)a bf
• lit(ndotl, ndoth, m) returns Blinn model
  ambient, diffuse, specular,1
• length(x), distance(x1,x2), pow(x,y), etc.

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Simple fp20 Bump Mapping

• Goal Bumpy Earth
• What should the FP do?
• Vertex inputs?
• Uniform Parameters?
• Outputs?
• Code?

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Simple fp20 Bump Mapping

• Goal Bumpy Earth
• What should the VP do?
• Inputs?
• Uniform Parameters?
• Textures?
• Code?

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Texture reads in Cg

• Need uniform parameter for the texture itself
  sampler2d, sampler3d, etc.
• Need to call appropriate texture read function,
  with appr. Params tex2d(my2dTexture, myCoords)

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Simple fp20 Bump Mapping

• Texture read code (out of context)
• float2 decalCoords TEXCOORD0
• uniform sampler2D decal, etc.
• float3 decalColor tex2D(decal,
  IN.decalCoords).rgb
• OpenGL side will be covered next week!

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Bump Reflection Mapping

• Goal Achieve reflection using normal map,
  environment map
• What kind of textures will we use?

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Bump Reflection Mapping

• float4 normal tex2D(NormalMap)
• Color texCUBE_reflect_dp3x3(EnvironmentMap,
  TangentToCubeSpace0, TangentToCubeSpace1,
  normal)
• transforms the normal, computes the reflected
  vector, and uses that to lookup into cubemap.

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Thin Film Interference

• Goal
• produce thin film color patterns (think oil or
  soap bubbles)
• Plan
• calculate the depth of film on the surface of
  object, based on view/normal angle
• Use depth as lookup and get color, use that to
  modify specular component

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Bump Horizon Mapping

• Goal bump mapping with self-shadowing
• Theory create horizon maps that store the
  elevation angle needed in a particular direction
  at each point
• Use the horizon maps nearest the light direction
  to find elevation, compare to light vector

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Bump Horizon Mapping

• Can encode 4 horizon maps in one texture, with 1
  elevation in each RGBA value.
• Thus horizon maps for 8 cardinal directions (N,
  NE, etc.) can be encoded nicely in 2 textures

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Car Paint

• Goal Make realistic car paint
• Fresnel effect
• Flecks in paint
• Wavy normals
• Reflection
• Fancy paint BRDF
• Plan Use a ton of textures

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Bumpy Shiny Patch

• Goal (go watch it!)
• What mapping effects are being used?

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Other possibilities?

• Iridescence color is view dependent
• Gloss mapping reflectivity differs over object
• Height field, offset bump maps
• Be creative! Be clever!

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Resources

• Cg User Manual
• http//developer.nvidia.com/object/cg_users_manual
  .html
• Also in Cg Toolkit folder
• Cg Browser download
• http//developer.nvidia.com/object/cg_toolkit.html
  
• Part of the Cg Toolkit (100 MB)