CS 445: Topics for Oct 2/4/6, 2017

• Exam 1 is Wednesday. We will review on Monday. See review sheet

• Lab:

  • Complete: Lab 4: Navigation
  • Begin: Lab 5: Lighting and Shading

• Phong Lighting

  • Resources: Phong Lighting, Ray Tracing Notes (pdf), and see other handouts.
  • What properties do we need to calculate the lighting:
    • Lighting properties (color, intensity, location)
    • Material properties: color, specularity, coefficients of reflection (ambient, diffuse, specular)
    • Surface normals for all geometric shapes.
      • Note, if you have the equation of your surface f(x,y,z), the normal is the gradient of f: normal to f = ∇ f = ( ∂ f/ ∂x, ∂ f/ ∂y, ∂ f/ ∂z)

      • How do Normals transform? When do we need to be careful?

    • The halfway vector, H, is used to approximate the specular product V dot R. You can read about the halfway vector.

  • For an entertaining lecture on lighting, see Knoll's Computer Class, episode 1

• In WebGL

  • We use attribute and uniform variables to store the normals, lighting and material properties.
  • Lighting calculations are done in the shaders:
    • Gouraud Shading: Phong lighting calculations done (per vertex) in the vertex shader and interpolated over fragments
    • Phong Shading: Phong lighting calculations done (per fragment) in the fragment shader.

• Recall: Shaders in the Rendering Pipeline:

  

• Look at Lab 5 code to see how this is all done.

• Setting the light position takes thought:

  • The Vertex Shader assumes the light position is in Camera (Eye) Coordinates.
  • Relative to Camera: Do you want the light position to be relative to the camera (i.e. Eye Coordinates)? If so, the position you set in the application should be interpreted as being relative to the camera. As such, you don't need to transform light position in application, rather just send it along as is to the shader via the uniform variable.
  • Relative to World: Do you want the light position to be relative world (World Coordinates)? If so, the position you set in the application should be interpreted as being relative to the World. You therefore need to transform light position in application from World to Eye Coordinates before sending to along to shader via the uniform variable.

• Normal vectors do not generally transform the same way that vertices transform. When do we need to be careful?

• Setting Up Shaders in Application - see Lab 5 code

• Shader Language (GLSL)

  • Quick Reference Card (GLSL is on pp 3-4, setting up shaders is on left column of p 2 ).
  • See handouts.

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