[Graphic Science] Chapter 8.7.2 Liang Youdong-barsky segment clipping algorithm

This section simply introduces the principle of Liang Youdong-barsky clipping algorithm, only the conclusion and no process, read http://blog.csdn.net/daisy__ben/article/details/51941608 This article, probably have a new understanding.

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The necessary and sufficient conditions for the existence of a common part (visible part) of the p1p2 and the Blue clipping window w1w2 (between the blue lines) are x1,x2,w1,w2 for the point p1p2w1w2, respectively:

Max (min (x1,x2), Min (w1,w2)) ≤min (Max (X1,X2), Max (W1,W2)) that is, the small person in the <= right end of the so-called left end.The points on the segment meet Y=x1+u (X2-X1) = x1 + u* x.　　Which 0<=u<=1. U1 determines the left point of the segment within the clipping area, and U2 determines the point to the right in the cropping area.　　Left point yl = x1 + u1 * x, right point yr = x1 + U2 * x, and must meet 0 <= U1 <= U2 <= 1. At this point, the solution of U1 and U2 is the purpose of the Liang Youdong-barsky segment clipping algorithm, (8.18) (8.19) for the formula in the book (8.18), the equation, that is, the intersection of the line segment and 4 boundaries U value. " R is not equal to 0, for the above four inequalities, when RK < 0 o'clock, U >= qk/rk, when rk>0 u <= qk/rk, then point P can be located within the cropping window. Similarly, if p already falls within the clipping window, you must be greater than or equal to the maximum value of the UK for all rk<0, and less than the UK minimum value corresponding to all rk>0. The code therefore has the function Glint cliptest (glfloat p, glfloat q, Glfloat * U1, Glfloat * U2). When p<0, to obtain the corresponding U, if the u>u2, then discard; if U<u2 and u>u1, then U1=u. If p>0, if the u<u1 is discarded, if u<u2, then u2=u. The incoming p,q are determined by the formula (8.19), respectively. This is calculated up to 4 times to obtain U1 and U2.

1#include <GLUT/GLUT.h>2#include <iostream>3#include"lineliangbarsk.h"4#include"Linebres.h"5 6Glint Cliptest (glfloat p, glfloat q, Glfloat * U1, Glfloat *U2)7 {8 glfloat R;9Glint returnvalue =true;Ten      One     if(P <0.0) A     { -R = Q/p; -         if(R > *U2) the         { -ReturnValue =false; -         } -         Else +         { -             if(R > *U1) +             { A*U1 =R; at             } -         } -     } -     Else -     { -         if(P >0.0) in         { -R = Q/p; to             if(R < *U1) +             { -ReturnValue =false; the             } *             Else $             {Panax Notoginseng                 if(R < *U2) -                 { the*U2 =R; +                 } A             } the         } +         Else -         { $             if(Q <0.0) $             { -ReturnValue =false; -             } the         } -     }Wuyi     returnreturnvalue; the } -  Wu voidLineclipliangbarsk (wcpt2d winmin, wcpt2d Winmax, wcpt2d p1, wcpt2d p2) - { AboutGlfloat u1 =0.0, U2 =1.0, dx = P2.getx ()-p1.getx (), DY; $      -     if(Cliptest (-DX, P1.getx ()-Winmin.getx (), &AMP;U1, &U2)) -     { -         if(Cliptest (DX, Winmax.getx ()-P1.getx (), &AMP;U1, &U2)) A         { +DY = p2.gety ()-p1.gety (); the             if(Cliptest (-dy, P1.gety ()-winmin.gety (), &AMP;U1, &U2)) -             { $                 if(Cliptest (Dy, winmax.gety ()-p1.gety (), &AMP;U1, &U2)) the                 { the                     if(U2 <1.0) the                     { theP2.setcoords (P1.getx () + U2 * dx, p1.gety () + U2 *dy); -                     } in                     if(U1 >0.0) the                     { theP1.setcoords (P1.getx () + u1 * dx, p1.gety () + u1 *dy); About                     } the Linebres (Round (P1.getx ()), round (P1.gety ()), round ( p2.getx ()), round (P2.gety ())); theStd::cout <<"Liangbarsk:"<< U1 <<","<< U2 <<Std::endl; theStd::cout <<"Liangbarsk:"<< P1.getx () <<","<< p1.gety () <<","<< P2.getx () <<","<< p2.gety () <<Std::endl; +                 } -             } the         }Bayi     } the}

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Reference: http://blog.csdn.net/daisy__ben/article/details/51941608

[Graphic Science] Chapter 8.7.2 Liang Youdong-barsky segment clipping algorithm