3D graphics eBook - Course Materials Repository
3D graphics eBook - Course Materials Repository
3D graphics eBook - Course Materials Repository
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Viewing frustum 233<br />
Viewing frustum<br />
In <strong>3D</strong> computer <strong>graphics</strong>, the viewing frustum or view frustum is the<br />
region of space in the modeled world that may appear on the screen; it<br />
is the field of view of the notional camera. The exact shape of this<br />
region varies depending on what kind of camera lens is being<br />
simulated, but typically it is a frustum of a rectangular pyramid (hence<br />
the name). The planes that cut the frustum perpendicular to the viewing<br />
direction are called the near plane and the far plane. Objects closer to<br />
the camera than the near plane or beyond the far plane are not drawn.<br />
Often, the far plane is placed infinitely far away from the camera so all<br />
objects within the frustum are drawn regardless of their distance from<br />
the camera.<br />
Viewing frustum culling or view frustum culling is the process of<br />
removing objects that lie completely outside the viewing frustum from<br />
A View Frustum<br />
the rendering process. Rendering these objects would be a waste of time since they are not directly visible. To make<br />
culling fast, it is usually done using bounding volumes surrounding the objects rather than the objects themselves.<br />
Definitions<br />
VPN<br />
VUV<br />
VRP<br />
PRP<br />
VRC<br />
the view-plane normal – a normal to the view plane.<br />
the view-up vector – the vector on the view plane that indicates the upward direction.<br />
the viewing reference point – a point located on the view plane, and the origin of the VRC.<br />
the projection reference point – the point where the image is projected from, for parallel projection, the PRP is<br />
at infinity.<br />
the viewing-reference coordinate system.<br />
In OpenGL, the viewing frustum is commonly set with the gluPerspective() [1] (or glFrustum() [2] )utility<br />
function.<br />
The geometry is defined by a field of view angle (in the 'y' direction), as well as an aspect ratio. Further, a set of<br />
z-planes define the near and far bounds of the frustum.<br />
References<br />
[1] OpenGL SDK Documentation: gluPerspective( ) (http:/ / www. opengl. org/ sdk/ docs/ man/ xhtml/ gluPerspective. xml) -- Accessed 9 Nov<br />
2010<br />
[2] OpenGL Programming Guide (Red Book) (http:/ / fly. cc. fer. hr/ ~unreal/ theredbook/ appendixg. html) -- Accessed 4 Jan 2011
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