3D Graphics Programming with QuickDraw 3D 1.5.4

Types of Pick Objects

A pick object is of type TQ3PickObject , which is one of the basic types of QuickDraw 3D objects. QuickDraw 3D defines several subtypes of pick objects, which are distinguished from one another by the pick geometry.

QuickDraw 3D provides two types of screen-space pick objects: window-point pick objects and window-rectangle pick objects. These pick objects test for closeness between the pick geometry (a point or rectangle in a window) and the screen projections of the objects in the model. In general, you'll use one of these two screen-space pick objects when using picking as the basis of user interaction.

There are many optimizations that can be used to determine whether an object in a model is suitably close to a pick geometry without having to perform all the projections that otherwise would be required. QuickDraw 3D uses these optimizations whenever appropriate.