Color, Projections, and Viewports

Tom Kelliher, CS 320

Feb. 23, 2009

Administrivia

Announcements

Project 1 due Wednesday.

Assignment

Read Chapter 3.1-3.3, 3.6.

From Last Time

2-D OpenGL lab.

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:

$$(x, y, z) \rightarrow (x, y, 0)$$

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

Viewports

What happens when the aspect ratio 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.)

Tom Kelliher