//每个线段的两点都在另一个线段的左右不同侧，则能断定线段相交 //公式对于向量(x1,y1)->(x2,y2),判断点(x3,y3)在向量的左边,右边,还是线上. //p=x1(y3-y2)+x2(y1-y3)+x3(y2-y1).p<0 左侧, p=0 线上, p>0 右侧
//计算点到线段的最短距离 double x1, y1, x2, y2, x3, y3; double px = x2 - x1; double py = y2 - y1; double som = px * px + py * py; double u = ((x3 - x1) * px + (y3 - y1) * py) / som;
// 是否高清屏 #define isRetina ([UIScreen instancesRespondToSelector:@selector(currentMode)] ? CGSizeEqualToSize(CGSizeMake(640, 960), [[UIScreen mainScreen] currentMode].size) : NO)
