CS488 - Introduction to Computer Graphics - Lecture 26

Comments and Questions


Review

  1. Distribution Ray Tracing
  2. Bi-directional ray tracing
  3. Office hours

Lighting

Participating Media

What is fog?

What is beer?

What they have in common is

What happens to the light that doesn't make it through?

Shadows

What is a shadow?

Shadows come `for free' in the ray tracer.

Yes. The methods, in increasing order of cost.

  1. Projective shadows

    Notice that we know a lot about how to project.

  2. Shadow maps

    How does this interact with scan conversion?

    What if the light is inside the view frustrum?

  3. Shadow volumes

Comment on global illumination. If you are doing a walk-through, you can calculate the illumination on each polygon once, then re-project the scene from different viewpoints as the user moves around.

Light Fields

This is a way to avoid even the need to re-project.

Let's turn our attention away from the surfaces of objects and onto the volume between objects

At every point in this volume there is a light density

This quantity L(P, theta, lambda ) is the light field. If we knew it we could

The evaluation is, in fact, just a projective transformation of the light field.

How do we get the light field?

  1. by measurement
  2. by calculation

How is the light field used in 2007?

But tomorrow!!

Radiosity


Surface Properties

Texture Mapping

  1. Basic
    1. Start with a 2D image: pixellated or procedural
    2. Map 2D image onto primitive using a 2D affine transformation
      • Simple if the surface of the primitive is flat
      • otherwise, ...
      • Texture pixels normally do not match display pixels, so some image processing may be needed.
    3. Backwards map intersection point with ray into the image to get the surface properties
  2. Normal Mapping (Bump mapping)
    1. Start with a difference surface, defined with respect to the surface
    2. Calculate the normals to the difference surface and map them onto the surface of the primitive
    3. Use the mapped surface models for lighting
    4. No occlusion, shadows are wrong, silhouettes are wrong, nobody notices!
  3. Solid Textures
    1. Solution to mapping texture onto curved surfaces
    2. Usually procedural

(Un)natural Phenomena

Refraction

Subsurface Scattering


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