Chapter 11. Picking and Selecting

GL provides two related mechanisms for returning information about where primitives are being drawn:

• List of GL Picking and Selecting Subroutines
• Picking
• Selecting

Picking returns all primitives that are currently being drawn in the vicinity of the cursor. Selecting returns all primitives that are being drawn into a 3-D rectilinear volume in world space. Both methods return the same type of data and use the same general mechanism for their operation. They differ in the way that the picking region or selecting volume is specified.

There are three concepts behind picking/selecting:

• The picking/selecting region is the area of the screen (for picking) or of world space (for selecting) that is sensitized.
• The format of the returned data is controlled by the name stack and the routines that manipulate the name stack.
• The method of structuring a program to make use of picking/selecting.