Line clipping
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The document discusses the Cohen-Sutherland line clipping algorithm. It describes how the algorithm performs initial tests on a line to determine if intersection calculations are needed by checking for trivial acceptance or rejection of line segments. If a line cannot be fully accepted or rejected, it is divided at a clip edge and the process is repeated iteratively until the line is fully processed. An example of applying the algorithm to clip a line against a rectangle is also provided.
Line clipping
- 1. Computer Graphics Line Clipping • Cohen Sutherland Algorithm (Line)
- 2. ( x min , y min ) ( x max , y max ) x = x min x = x max y = y min y = y max ( x 1 , y 1 ) clip rectangle maxmin maxmin yyy xxx ≤≤ ≤≤ For a pointFor a point ((x,yx,y)) to be inside the clip rectangleto be inside the clip rectangle:: Point Clipping
- 3. clip rectangle ( x a , y a )( x b , y b ) ( x c , y c ) ( x d , y d ) ( x 0 , y 0 ) ( x 1 , y 1 ) ( x , y ) clip rectangle ( x a , y a )( x b , y b ) ( x c , y c ) ( x d , y d ) ( x 0 , y 0 ) ( x 1 , y 1 ) ( x , y ) ( ) ( ) 1 1 1 1 1 1 1 1 1 : , 0, : ( ) , 1 : , 0, : ( ) , T L B R Top x x y y m Left y m x x y m m Bottom x x y y m Right y m x x y m m = + − ≠ = − + ≠∞ = + − ≠ = − + ≠∞ Line Clipping
- 4. 0000 1000 0100 1001 1010 0001 0010 0101 0110 clip rectangle Region outcodesRegion outcodes min max yy yy < > :1bit :0bit min max xx xx < > :3bit :2bit Cohen-Sutherland Algorithm
- 5. The Cohen-Sutherland Line-Clipping Algorithm performs initial tests on a line to determine whether intersection calculations can be avoided. 1. First, end-point pairs are checked for trivial Acceptance. 2. If the line cannot be trivially accepted, region checks are done for Trivial Rejection. 3. If the line segment can be neither trivially accepted or rejected, it is divided into two segments at a clip edge, so that one segment can be trivially rejected. These three steps are performed iteratively until what remains can be trivially accepted or rejected. Cohen-Sutherland Algorithm
- 6. Cohen-Sutherland Algorithm Algorithm 1-Compute the codes for the Two end points 2-Enter in loop, check if both region codes are zero(0000 and 0000) put line in display file for display and exit loop, return 3-If both region codes are not zero then take logical AND of both codes, check result for nonzero if so reject line exit loop, return 4-If result is zero then subdivide the line from intersection point of line and clipping boundary and repeat step 2,3,4. 5. Special Case when test 4 fails.
- 10. An ExampleAn Example clip rectangle B C Cohen-Sutherland Algorithm
- 11. Q1. Use Cohen Sutherland Algorithm to clip line p1(70,20) and P2 (100,10) against window lower left hand corner (50,10) and upper right hand corner (80,40). Q2. Given a clipping window A(20,20), B(60,20), C(60,40), D(20,40). Using sutherland cohen algorithm find the visible portion of line segment joining the points p(40,80),Q(120,30).
- 12. Thank You