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Next: 1.18 Sampling Algorithms Up: 1. Functionality Previous: 1.16 Animation

# 1.17 Motion Blur

There are two different motion blur algorithms. One is completely general and computes motion blur of highlights, textures, shadows, reflections, refractions, transparency, and intersecting objects. The other algorithm is much faster, but cannot handle reflections and refractions (and shadows have to be approximated with shadow maps). However, motion blur of highlights, textures, transparency, and intersecting objects still work with the faster algorithm. The faster algorithm is used for scanline samples (first-generation non-raytraced).

The movement of objects is specified by associating linear motion vectors with polygon vertices and surface control points. These vectors give the direction and distance that the vertex or control point moves during one time unit. If a motion vector is not specified, the vertex is assumed to be stationary. Motion blurring computations may be expensive, but note that these computations are only done for those polygons in a scene which include motion information.

A shutter speed may be given for the camera with the `-shutter` option on the command line or `shutter` in the options statement, with the default speed of zero turning motion blurring off. The shutter opens instantaneously at time zero and closes after the shutter speed time has elapsed.