CSE 681 Reflection

1
CSE 681Reflection
2
Mirror Reflection

• Shiny Objects
• Perfect mirror in the extreme case
• Assume this for now mathematics easy for this
  nice case
• Reflect the view vector about the normal and cast
  a reflection ray

3
Reflection Ray

• Reflect the view vector about the normal, call it
  R
• We already know how to solve this

4
Raytracing With Reflection
secondary ray
L1
N1
primary ray
5
Raytracing With Reflection
Keep track of the depth of the ray tree

• Color shade( ray, recursionDepth )
• c background color
• intersectFlag FALSE
• for each object
• intersectFlag intersect ( ray, p )
• if intersectFlag is TRUE
• c ambient
• for each light source
• compute reflective ray R (or H)
• c diffuse
• c specular components
• if ( recursionDepth lt MAXRECURSION)
• if (object is shiny)
• compute reflection of the ray, R1
• c shininess shade( R1,
  recursionDepth 1 )
• return c

First illuminate the point
Dont spawn reflection ray past the pre-chosen
tree depth
R1 reflects the view vector Add the returned
color with a shininess factor
6
Reflection Problem

• Something should rub you the wrong way
• Oh yeah, that pesky precision problem again!
• How shall we perturb the intersection point?
• In the direction of the reflection vector

No epsilon
With epsilon
7
Improved Reflection

• Our shininess constant attenuates the returned
  color based on the objects shininess
• Not a great approximation
• Light is partially reflected and refracted
• Refractive Index ? sin f / sin ?
• Depends on the object material

8
Fresnel Equation

• The reflectance F of a perfectly smooth surface
  in terms of refractive index ? of the material
  and the angle of incidence ?
• F0 ( ? - 1 )2 / ( ? 1 )2, for ? 0
• Depends on the material
• For example, burnished copper has roughly
• F0,blue 0.1, F0,green 0.2, F0,red 0.5
• F? F0 ( 1 - cos ? )5 ( 1 - F0 ), for 0 lt ? lt
  90
• As ? increases, F? increases
• F90 1, the light is tangential to the surface

Also called Schlicks Approximation
9
Fresnel Equation

• Dielectric clear material that refracts light

metal
glass (dielectric)
10
Fresnel Reflectance

• Lafortune et al.