CG Basics - An Introduction to Computer Graphics for Artists - page 19

Table 2.3 Snap modes

Snaps Snaps to

Grid Grid line intersections

Curve Curves

Vertex Single vertex

Edge Center of edge

Face Center of face

Object Center of object

Fig. 2.13 Backface culling removes the display of edges that are blocked by other objects.
The cube on the left is drawn with occlusion culling turned on. The cube on the right is drawn
without occlusion culling

2.3.9 Draw Modes

In your application, look for a tool or a button that will allow you to create a cube.
Invoke the command and a cube will appear on your screen, drawn in wireframe.
Wireframe is a way to represent an object in line only. It draws vertices and then
connects them with straight lines. Because these are drawn in real-time, they are
usually drawn at very low quality (Bærentzen et al. 2008 ). Some programs allow
you to turn backfacing on or off. This option allows you to turn off the display of
faces that are behind other faces. This is called occlusion culling because faces that
are blocked, or are facing away from the camera, are not drawn (Fig. 2.13 ). The
term backface culling is similar, but only refers to faces that are oriented away from
the camera. In practice, the backface culling option will also cull occluded faces,
even if they are not turned away from the camera but are blocked by other objects.
The result is that many extraneous edges are removed from the scene. This reduces
visual confusion that would have resulted from seeing both sides of your objects
at the same time, or many layers of overlapping objects (Yoon et al. 2004 ; Laine
and Karras 2011 ).