Page 147 - DCAP504_Computer Graphics

Computer Graphics

Figure 9.8: Line Clipping

Consider the above two lines AD and EI. Clip the above two lines such that the line
segment DC and HG are visible. You need to show the clipping process using (a)
Cohen Sutherland algorithm and (b) Midpoint Subdivision algorithm.

9.4 Summary
• Clipping is used to display the images within the window frame.

• Clipping algorithm is the procedure used to determine whether the portion of the object lies
within or outside the window frame.
• Point clipping and line clipping are the two most common types of clipping.
• Point clipping removes the points that lie outside the window.

• Line clipping determines whether the line lies within or outside the clipping window and removes
the line segments that lie outside the window.
• Line clipping includes three algorithms used to determine the line visibility, namely Cohen
Sutherland Algorithm, Midpoint Subdivision Algorithm and Liang-Barsky Algorithm.

• Cohen Sutherland Algorithm determines whether the line is visible, invisible or clipping
candidate.
• If the line is clipping candidates then Cohen Sutherland algorithm performs calculation of the
intersection of the line with the window edge.
• Midpoint Subdivision Algorithm avoids the calculation involved Cohen Sutherland algorithm by
simply subdividing the line at its midpoint until the line segment is completely visible or
completely invisible.
• Liang-Barsky Algorithm based on analysis of the parametric line equations.

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