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Cohen-Sutherland Line Clipping Algorithm: When drawing a 2D line on screen, it might happen that one or both of the endpoints are outside. The primary use of clipping in computer graphics is to remove objects, lines, or line This algorithm is more efficient than Cohen-Sutherland algorithm. Department of Computing Science, Umeå University. Computer Graphics & Visualization. Overview. Clipping. ▫ Cohen-Sutherland line clipping algorithm.

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The bits in the 2D outcode represent: To determine whether endpoints are inside or outside a window, the algorithm sets up a half-space code for each endpoint. These 4 bits represent the Top, Bottom, Right, and Left of the region as shown in the following figure.

It depends on the methods used to generate characters and the requirements of a particular application. Line can be completely outside of the window This line will be completely removed from the region. For other convex polygon clipping windows, use the Cyrus—Beck algorithm.

Cohen Sutherland Line Clipping Algorithm in C and C++ – The Crazy Programmer

For better understanding let us consider the following example where we draw a smiley face using bit-map graphics. The code’s bits are set cliping to the following conditions:. For example, if an endpoint had a code of while the other endpoint had a code ofthe logical AND would be which indicates the line segment lies outside of the window.


The primary use of clipping in computer graphics is to remove objects, lines, or line segments that are outside the viewing pane. Views Read Edit View history.

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.

Once we establish region codes for both the endpoints of a line we determine whether the endpoint is visible, partially visible or invisible with the help of ANDing of the region codes.

Viewing & Clipping

By using this site, you agree to the Terms of Use and Privacy Policy. If both endpoints of a line lie inside the window, the entire line lies inside the window. We will use 4-bits to divide the entire region.

If both codes arebitwise OR of the codes yields line lies completely inside the window: First the polygon is clipped against the left edge of the polygon window to get new vertices of the polygon. A bitmap is a collection of pixels that describes an image. If the character is on the boundary of the clipping window, then we discard that entire character and cclipping the rest string.

It can be trivially rejected. While processing an edge of a polygon with clipping window, an intersection point is found if edge is not completely inside clipping window and the a partial edge from the intersection point to the outside edge is clipped.

The Cohen—Sutherland algorithm can be used only on a rectangular clip window. This is one of the oldest and most popular line clipping algorithm. To speed up the process this algorithm performs initial tests that reduce number of intersections that must be calculated. Various techniques are used to provide text clipping in a computer graphics.


An outcode is computed for each of the two points in the line. If it is partially outside the window, then. The Cohen-Sutherland algorithm uses a divide-and-conquer strategy. To perform the trivial acceptance and rejection tests, we extend the edges of the window to divide the plane of the window into the nine regions. In this method if the string is entirely inside the clipping window, then we keep it.

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

Cohen Sutherland Line Clipping Algorithm in C and C++

If the region is to the top of the window, the second bit of the code is set to 1. This algorithm uses the clipping window as shown in the following figure.

If both codes have a 1 in the same bit position bitwise AND of the codes is notthe line lies outside the window.