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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To determine whether endpoints are inside or outside a window, the algorithm sets up a half-space code for each endpoint. For example, if an endpoint had a code of while the other suthherland had a code ofthe logical AND would be which indicates the line segment lies outside of the window.

For any endpoint xy of a line, the code can be determined that identifies which region the endpoint lies. On the other hand, if both endpoints of a line lie entirely to one side of the window, the line must lie entirely outside of the window.

The concept of line clipping is same as point clipping. This process is continued until the line is accepted. A polygon can also be clipped by specifying the clipping window. Line can be partially inside the window We will find intersection point and draw only that portion of line that is inside region. In this algorithm, all the vertices of the polygon are clipped against each edge of the clipping window.

To speed up the process this algorithm performs initial tests that reduce number of intersections that must be calculated. Various techniques are used cohwn provide text clipping in a computer graphics.

Cohen Sutherland Line Clipping Algorithm in C and C++

Learn how your comment data is processed. The primary use of clipping in computer graphics is to remove objects, lines, or line segments that are outside the viewing pane. It is trivially accepted and needs no clipping. Garphics the polygon is clipped against the left edge of the polygon window to get new vertices of the polygon. Retrieved from ” https: This clipping method is based on characters rather than the entire string. The bits in the 2D outcode represent: The 4 bits in the code then identify each of the nine regions as shown below.


The line segment’s endpoints are tested to see if the line can be trivally accepted or rejected. In line clipping, we will cut the portion of line which is outside of window and keep only the portion that is inside the window.

It is trivially rejected and needs algoritum be neither clipped nor displayed. As you proceed around the window, extending each edge and defining an inside half-space and an outside half-space, nine regions are created – the eight “outside” regions and the one “inside”region. By observing the original smiley face closely, we can see that there are two blue lines which are represented as B1, B2 and E1, E2 in the above figure.

If the region is to the top of the window, the second bit of the code is set to 1. It does so by using a 4 bit code called as region code or outcodes.

In this method if the string is entirely inside the clipping window, then we keep it.

Cohen-Sutherland Line-Clipping Algorithm

For example, if the endpoint codes are andthe logical OR is – the line can be trivally accepted. The first bit is set to 1 if the point is above the viewport.

This algorithm is more efficient than Cohen-Sutherland algorithm. 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.

On the other hand, if the endpoints had codes of andthe logical AND would beand the line could not be trivally rejected. If the character is on the boundary of the clipping window, then we discard only that portion of character that is outside of the clipping window.


Reject line segment if any end point of line appears outside of any boundary.

This site uses Akismet to reduce spam. The Cohen—Sutherland algorithm can be used only on a rectangular clip window. Sutherland Hodgeman polygon clipping algorithm is used for polygon clipping. Your email address will not be published. If the endpoint codes are andsktherland logical OR is and the line can not be trivally accepted. Leave a Reply Cancel reply Your email address will not be published.

This clipping method is based on characters rather than entire string. An outcode is computed for each of the two points in the line.

Each end point of the line segment is then assigned the code of the region in which it lies. This page was last edited on 7 Januaryat The algorithm was developed in during flight-simulator work by Danny Cohen and Ivan Sutherland. Consider the following figure, where the rectangle indicates the window. Once the codes for each endpoint of a line are determined, the logical AND operation of the codes determines if the line is completely outside of the window.

Line can be completely outside of the window This line will be completely removed from the region. Note that the outcodes for endpoints must be recalculated on each iteration after the clipping occurs. The Cohen-Sutherland algorithm uses a divide-and-conquer strategy. If the character is on the boundary of the clipping window, then we discard that entire character and keep the rest string.