Cohen-Sutherland

The Cohen–Sutherland algorithm is a computer-graphics algorithm used for line clipping. The algorithm divides a two-dimensional space into 9 regions and then efficiently determines the lines and portions of lines that are visible in the central region of interest (the viewport).

The algorithm was developed in 1967 during flight-simulator work by Danny Cohen and Ivan Sutherland.

The algorithm includes, excludes or partially includes the line based on whether:

The numbers in the figure below are called outcodes. An outcode is computed for each of the two points in the line. The outcode will have 4 bits for two-dimensional clipping, or 6 bits in the three-dimensional case. The first bit is set to 1 if the point is above the viewport. The bits in the 2D outcode represent: top, bottom, right, left. For example, the outcode 1010 represents a point that is top-right of the viewport.

Note that the outcodes for endpoints must be recalculated on each iteration after the clipping occurs.

The Cohen–Sutherland algorithm can be used only on a rectangular clip window. For other convex polygon clipping windows, use the Cyrus–Beck algorithm.

Algorithms used for the same purpose:

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