Page 140 - DCAP504_Computer Graphics

Unit 9: Clipping I

In figure 9.3, the above three categories are clearly differentiated.

Figure 9.3: Line Categories

In figure 9.3, the line LM falls under category 1 (Visible). The lines OP and QR fall under category 2
(Invisible) and the lines ST and AB fall under category 3 (Clipping candidate).
The Cohen Sutherland algorithm provides an efficient way to determine the category of a line. The
algorithm divides the procedure into two steps:
1. Step 1: A 4-bit binary code called region code is assigned to each endpoint of the line. The
endpoints lie in any of the nine regions of the plane. Figure 9.4 shows the 4-bit region codes that
are assigned to every endpoint of the line depending on its position in 2-D space.

Figure 9.4 : Region Codes

Each bit of the code is set either true (1) or false (0) according to the following scheme.

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