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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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It does so by using a 4 bit code called as region code or outcodes.

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 bits in the 2D outcode represent: If the character is on the boundary of the clipping window, then we discard that entire character and keep the rest string. Read 2 corner points of the clipping window left-top and right-bottom as wx1,wy1 and wx2,wy2.

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. If it is partially outside the window, then. Note that the outcodes for endpoints must be recalculated on each iteration after the clipping occurs.

It employs parametric line representation and simple dot products.

For better understanding let us consider the following example where we draw a smiley face using bit-map graphics. If both codes have a 1 in the same bit position bitwise AND of the codes is notthe line lies outside the window. The line segment’s endpoints are tested to see if the line can be trivally accepted or rejected.

Retrieved from ” https: For any endpoint xy of a line, the code can be determined that identifies which region the endpoint lies. Each end point of the line segment is then assigned the code of the region in which it lies. To clip a line, we need to consider only its endpoints. The logical OR of the endpoint codes determines if the line is completely inside the window.


If the region is to the left of the window, the first bit of the code is set to 1.

Reject line segment if any end point of line appears outside of any boundary. By observing the original smiley face closely, we can see that there are two blue lines which suthedland represented as B1, B2 and E1, E2 in the above figure. It is trivially accepted and needs no clipping. This algorithm is more efficient than Cohen-Sutherland algorithm.

Leave a Reply Cancel reply Your email address will not be published. The code’s bits are set according to the following conditions:.

Cohen–Sutherland algorithm – Wikipedia

Clipping a point from a given window is very easy. It agorithm a type gaphics computer graphics that the computer uses to store and display pictures. Let N i be the outward normal edge E i. For example, the outcode represents a point that is top-right of the viewport. The Cohen-Sutherland algorithm uses a divide-and-conquer strategy.

These codes identify location of the end point of line. The numbers in the figure below are called outcodes. 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.

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.

Views Read Edit View history. Now pick any arbitrary point P Ei on edge E i then the dot product N i. The 4 bits in the algodithm then identify each of suthwrland nine regions as shown below. 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.


Cohen-Sutherland Line Clipping The Cohen-Sutherland line clipping sutherlanf quickly detects and dispenses with two common and trivial ustherland. 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 compiter. First the polygon is clipped against the left edge of the polygon window to get new vertices of the polygon.

To speed up the process this algorithm performs initial tests that reduce number of intersections that must be calculated. On the other hand, if the endpoints had codes of andthe logical AND would beand the line could not be trivally rejected. If to the rightthe third bit is set, and if to the bottomthe fourth bit is set. If the logical AND of the endpoint codes is not zerothe line can be trivally rejected. Cohfn 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.

Viewing & Clipping

If both endpoints of a line lie inside the window, the entire line lies inside the window. This algorithm uses the clipping window as shown in the following computee.

The algorithm was developed in during flight-simulator work by Danny Cohen and Ivan Sutherland. Line can be partially inside the window We will find intersection point and draw only that portion of line that is inside region. In all or none string clipping method, either we keep the entire string or we reject entire string based on the clipping window.

Consider the following figure, where the rectangle indicates the window. You May Also Like:


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