COHEN SUTHERLAND LINE CLIPPING ALGORITHM IN COMPUTER GRAPHICS PDF

The algorithm divides a 2D space into 9 regions, of which only the middle part viewport is visible. In , flight-simulation work by Danny Cohen led to the development of the Cohen—Sutherland computer graphics two- and three-dimensional line clipping algorithms, created with Ivan Sutherland. Main article: Liang—Barsky algorithm The Liang—Barsky algorithm uses the parametric equation of a line and inequalities describing the range of the clipping box to determine the intersections between the line and the clipping box. With these intersections it knows which portion of the line should be drawn.

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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. It does so by using a 4 bit code called as region code or outcodes. These codes identify location of the end point of line.

Each bit position indicates a direction, starting from the rightmost position of each bit indicates left, right, bottom, top respectively. 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.

There arises 3 cases which are explained in the algorithm below in step 4. Algorithm 1. Read 2 end points of line as p1 x1,y1 and p2 x2,y2 2. Read 2 corner points of the clipping window left-top and right-bottom as wx1,wy1 and wx2,wy2 3. Check for visibility of line If region codes for both endpoints are zero then line is completely visible. Draw the line go to step 9. If region codes for endpoints are not zero and logical ANDing of them is also nonzero then line is invisible.

Discard the line and move to step 9. If it does not satisfy 4. Divide the line segments considering intersection points. Reject line segment if any end point of line appears outside of any boundary.

Draw the clipped line segment.

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Viewing & Clipping

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. It does so by using a 4 bit code called as region code or outcodes. These codes identify location of the end point of line. Each bit position indicates a direction, starting from the rightmost position of each bit indicates left, right, bottom, top respectively. 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. There arises 3 cases which are explained in the algorithm below in step 4.

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Cohen Sutherland Line Clipping Algorithm in C and C++

Next Page The primary use of clipping in computer graphics is to remove objects, lines, or line segments that are outside the viewing pane. Point Clipping Clipping a point from a given window is very easy. Consider the following figure, where the rectangle indicates the window. 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.

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