CMPT461 Final Project: Diffraction Shader

1
CMPT461 Final ProjectDiffraction Shader

• By Erif Setiadi

2
Iridescence

• An optical phenomenon characterized as the
  property of surfaces in which hue changes
  according to the angle from which surface is
  viewed Wikipedia, Iridescence
• Dispersion
• Diffraction
• Interference

3

• Diffraction

• One of the Iridescence phenomena that can occurs
  due to light wave travels into an arperture
  smaller than wavelength.
• Case of monochromatic lights -gt
• Case of polychromatic lights -gt Iridescence
  effect in CD
• Interference ! diffraction
• Interference caused by light wave traversing
  thin media of different indices of refraction

4

• Diffraction Shader

• Taken mainly from Jos Stams paper Diffraction
  Shaders
• (SIGGRAPH99)
• BRDF for periodic like surface (CD)
• Hard to be understood

• Simplified model for HLSL
• http//www.dgp.toronto.edu/stam/reality/Resear
  ch/Diffraction/vp.html
• No Fresnel term or environment mapping

5

• GLSL Implementation

• Vertex Shader
• Compute the anisotropy and diffracted ray light,
  as well as Fresnel factor
• Anisotropy
• Diffraction

6

• GLSL Implementation

• Vertex Shader
• Fresnel
• Conductor
• Dielectric
• Schlicks approximation

7

• GLSL Implementation

• Fragment Shader
• Compute the Phong Shading / Environment Mapping
• Phong Shading
• Environment Mapping
• Cube Mapping

8

• GLSL Implementation

• Fragment Shader
• Final output
• gl_FragColor vec4(color, 1.0) diffcolor

9

• Problems Founded

• CD Model
• Wrong diffraction direction -gt Remodel the CD

10

• Problems Founded

• Fresnel
• Fresnel term return a very high value at certain
  extreme angle
• Base BRDF
• Ward BRDF doesnt give high enough Illumination

11

• GLSL Implementation

• Pro
• GLSL Implementation easily adjusted parameters
• Environment map and Fresnel for realistic
  reflection
• Cons
• Limited temporary register.
• Phong BRDF -gt doesnt preserve conservation of
  energy

12

• DEMO

DEMO