Assignment 4 hints

General

• Parameter files
  • Use them! Make any variable you could ever possibly want to change when experimenting a parameter.
  • You can implement several ways of doing something as separate shaders - *or* introduce an integer or string valued variable to make a choice between implementations inside a shader.
• Document everything. We'll need to know what variables you used so we can see what they do.
• Start early!

Surface shaders

• Bump mapping
  • Take a look in the textbook for some really good fomulas (pg. 744)
  • Use a paint program to design bump images. Start with a black canvas and paint white shapes on it. Then, view it with xv and blur it (alot... use a blur size of at least 7).
  • Or, write a function that given parameter values (u,v), it returns a height value or a gradiant value.
  • Think about including a bumpScale parameter that will allow you to increase or decrease the effect the bumps have on your normal to make them easier to see.

• Wood & Marble
  • Our silly noise example used the noise function to modulate a color between black and white - ie. color = noise*otherColor. Use a linear interpolation formula (like you used in assignments 1 & 2) to modulate between two colors. Even better - figure out a way to modulate between three colors (it would make Andrew happy).

• Real surface
  • Combine the effects of many simpler shaders. Think about: bumps, color modulations (perhaps with a noise function), response to incoming light (is it a shiny surface? a matte surface?), etc.

Light shaders

• Projected textures
  • Use the "direction", "up" and "right" parameters for a light to aim your light source and orient your stencil image. (Actually, you only need two of the three, if you remember back to the lectures on transformations).
  • Implement a simple perspective projection of the points onto the stencil plane - ala screenx = x/z for 3D perspective renderings - so your projected light behaves properly. (see the online example)