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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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Point clipping tells us whether the given point X, Y is within the given window or not; and decides whether we will use the minimum and maximum coordinates of the window. Each of lin nine regions associated with the window is assigned a 4-bit code to identify the region.

Each bit in the code is set to either a 1 true or a 0 false. If to the rightthe third bit is set, and if to the sugherlandthe fourth bit is set. Each edge of the window defines an infinite line that divides the whole space into two half-spaces, the inside half-space and the outside half-spaceas shown below. If the character is on the boundary of the clipping window, then we discard that entire character and keep the rest string.

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.

Viewing and Clipping

Consider the following figure, where the rectangle indicates the window. Retrieved from ” https: 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. A bitmap is a collection of pixels that describes an image. Each bit position indicates a direction, starting from the rightmost position of each bit indicates left, right, bottom, top respectively. It is trivially accepted and needs no clipping.


For other convex polygon clipping windows, use the Cyrus—Beck algorithm. Note that the outcodes for endpoints must be recalculated on clupping iteration after the clipping occurs. Reject line segment if any end point of line appears outside of any boundary. An outcode is computed for each of the two points in the line. Let N i be the outward normal edge E i.

These codes identify location of the end point of line. It is a type of computer graphics that the computer uses to store and display pictures. If the region is to the left of the window, the first bit of the code is set to 1.

Read 2 corner points of the clipping window left-top and right-bottom as wx1,wy1 and wx2,wy2. 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.

Clipping a point from a given window is very easy. Your email address will not be published.

Cohen-Sutherland Line-Clipping Algorithm

We will use 4-bits to divide the entire region. 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. If both codes sutherlanc a 1 in the same bit position bitwise AND of the codes is notthe line lies outside the window. The algorithm was developed in during flight-simulator work by Danny Cohen and Ivan Sutherland.


To clip a line, we need to consider only its endpoints. In this algorithm, all the vertices of the polygon are clipped against each edge of the clipping window. The numbers in the figure below are called outcodes. Cohne the endpoint codes are andthe logical OR is and the line can not be trivally xohen.

Cohen–Sutherland algorithm

It depends on the methods used to generate characters and the requirements of a particular application. If the region is to the top of the window, the second bit of the code is set to 1.

You May Also Like: You can connect with him on facebook. The code’s bits are set according to the following conditions:.

Cohen-Sutherland Line Clipping The Cohen-Sutherland line clipping algorithm quickly detects and dispenses with two common and trivial cases. It does so by using a cohe bit code called as region code or outcodes.

Leave a Reply Cancel reply Your email address will not be published. These 4 bits represent the Top, Bottom, Right, and Left of the region as shown in the following figure.