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////  LineIntersect.h//  HungryBear////  Created by Bruce Yang on 12-3-12.//  Copyright (c) 2012年 EricGameStudio. All rights reserved.//#import 
     
      #import "Box2D.h"#define zero(x) (((x)>0?(x):-(x))
      
        b2_epsilon;}// 判两直线平行+(int) parallel:(b2Vec2)u1 u2:(b2Vec2)u2 v1:(b2Vec2)v1 v2:(b2Vec2)v2 {    return zero((u1.x-u2.x)*(v1.y-v2.y)-(v1.x-v2.x)*(u1.y-u2.y));}// 判三点共线+(int) dots_inline:(b2Vec2)p1 p2:(b2Vec2)p2 p3:(b2Vec2)p3 {    return zero([self xmult:p1 p2:p2 p3:p3]);}// 判两线段相交,包括端点和部分重合+(int) intersect_in:(b2Vec2)u1 u2:(b2Vec2)u2 v1:(b2Vec2)v1 v2:(b2Vec2)v2 {    if (![self dots_inline:u1 p2:u2 p3:v1] || ![self dots_inline:u1 p2:u2 p3:v2]) {        return ![self same_side:u1 p2:u2 l1:v1 l2:v2] && ![self same_side:v1 p2:v2 l1:u1 l2:u2];    } else {        return [self dot_online_in:u1 l1:v1 l2:v2] ||                 [self dot_online_in:u2 l1:v1 l2:v2] ||                 [self dot_online_in:v1 l1:u1 l2:u2] ||                 [self dot_online_in:v2 l1:u1 l2:u2];    } }// 计算两线段交点,请判线段是否相交(同时还是要判断是否平行!)+(b2Vec2) intersection:(b2Vec2)u1 u2:(b2Vec2)u2 v1:(b2Vec2)v1 v2:(b2Vec2)v2 {    b2Vec2 ret=u1;    double t=((u1.x-v1.x)*(v1.y-v2.y)-(u1.y-v1.y)*(v1.x-v2.x))    /((u1.x-u2.x)*(v1.y-v2.y)-(u1.y-u2.y)*(v1.x-v2.x));    ret.x+=(u2.x-u1.x)*t;    ret.y+=(u2.y-u1.y)*t;    return ret;}#pragma mark-#pragma mark 适用于 CGPoint 的版本~// 计算交叉乘积 (P1-P0)x(P2-P0)+(double) xmult2:(CGPoint)p1 p2:(CGPoint)p2 p3:(CGPoint)p0 {    return (p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y);}// 判点是否在线段上,包括端点+(int) dot_online_in2:(CGPoint)p l1:(CGPoint)l1 l2:(CGPoint)l2 {    return zero([self xmult2:p p2:l1 p3:l2]) &&     (l1.x-p.x)*(l2.x-p.x) < b2_epsilon &&     (l1.y-p.y)*(l2.y-p.y) < b2_epsilon;}// 判两点在线段同侧,点在线段上返回0+(int) same_side2:(CGPoint)p1 p2:(CGPoint)p2 l1:(CGPoint)l1 l2:(CGPoint)l2 {    return [self xmult2:l1 p2:p1 p3:l2] * [self xmult2:l1 p2:p2 p3:l2] > b2_epsilon;}// 判两直线平行+(int) parallel2:(CGPoint)u1 u2:(CGPoint)u2 v1:(CGPoint)v1 v2:(CGPoint)v2 {    return zero((u1.x-u2.x)*(v1.y-v2.y)-(v1.x-v2.x)*(u1.y-u2.y));}// 判三点共线+(int) dots_inline2:(CGPoint)p1 p2:(CGPoint)p2 p3:(CGPoint)p3 {    return zero([self xmult2:p1 p2:p2 p3:p3]);}+(int) intersect_in2:(CGPoint)u1 u2:(CGPoint)u2 v1:(CGPoint)v1 v2:(CGPoint)v2 {    if (![self dots_inline2:u1 p2:u2 p3:v1] || ![self dots_inline2:u1 p2:u2 p3:v2]) {        return ![self same_side2:u1 p2:u2 l1:v1 l2:v2] && ![self same_side2:v1 p2:v2 l1:u1 l2:u2];    } else {        return [self dot_online_in2:u1 l1:v1 l2:v2] ||         [self dot_online_in2:u2 l1:v1 l2:v2] ||         [self dot_online_in2:v1 l1:u1 l2:u2] ||         [self dot_online_in2:v2 l1:u1 l2:u2];    } }// 计算两线段交点,请判线段是否相交(同时还是要判断是否平行!)+(CGPoint) intersection2:(CGPoint)u1 u2:(CGPoint)u2 v1:(CGPoint)v1 v2:(CGPoint)v2 {    CGPoint ret=u1;    double t=((u1.x-v1.x)*(v1.y-v2.y)-(u1.y-v1.y)*(v1.x-v2.x))    /((u1.x-u2.x)*(v1.y-v2.y)-(u1.y-u2.y)*(v1.x-v2.x));    ret.x+=(u2.x-u1.x)*t;    ret.y+=(u2.y-u1.y)*t;    return ret;}#pragma mark-#pragma mark 验证上述几个方法的移植是否存在什么问题~+(void) validateIntersect:(b2Vec2)u1 u2:(b2Vec2)u2 v1:(b2Vec2)v1 v2:(b2Vec2)v2 {    b2Vec2 answer;    if ([self parallel:u1 u2:u2 v1:v1 v2:v2] || ![self intersect_in:u1 u2:u2 v1:v1 v2:v2]){        printf("无交点!\n");    } else {        answer = [self intersection:u1 u2:u2 v1:v1 v2:v2];        printf("交点为:(%lf,%lf)\n", answer.x, answer.y);    }}+(void) validateAlgorithm {    [LineIntersect validateIntersect:b2Vec2(0,1) u2:b2Vec2(1, 0) v1:b2Vec2(0, 0) v2:b2Vec2(1,1)];    [LineIntersect validateIntersect:b2Vec2(0,10) u2:b2Vec2(10, 0) v1:b2Vec2(0, 0) v2:b2Vec2(10,10)];    [LineIntersect validateIntersect:b2Vec2(-2,0) u2:b2Vec2(2, 0) v1:b2Vec2(-1, 3) v2:b2Vec2(-1, -1)];    [LineIntersect validateIntersect:b2Vec2(-2,0) u2:b2Vec2(2, 0) v1:b2Vec2(-1, 3) v2:b2Vec2(1, -2)];}@end