Color, Projections, and Viewports

Tom Kelliher, CS 320

Feb. 24, 2003

Administrivia

Announcements

Assignment

Read 3.1--3, 3.9.

From Last Time

Project day.

Outline

1. Color.

2. Projections.

3. Viewports.

4. Lab.

Coming Up

Interactive techniques.

Color

Additive color. Tristimulus values vs. continuous frequency of light.

Two color models:

1. RGB color.

   The color cube.

2. Indexed color.
   1. What is it? Why use it?

   2. Where is it used?

      In 8-bit mode, which 256 colors get displayed? Color map clashes in X Window system.

Orthographic Projection

Now we see the mapping:

glOrtho(GLdouble left, GLdouble right,
        GLdouble bottom, GLdouble top,
        GLdouble zNear, GLdouble zFar);

Viewports

What happens when the aspect ration of the clipping region doesn't match that of the window?

How can we fix that:

• Use a viewport (sub-window) on the window:

  glViewport(GLint x, GLint y, GLsizei width, GLsizei height);
  

  We have a call-back whose parameters are the size of the resized window.

  This essentially adjusts the window's aspect ratio to match the clipping region.

• Adjust the clipping region to match the window. Again, read the current window dimensions.

• Re-adjust the window size from the program. (Kinda obnoxious.)