更新时间:2022-06-20 23:45:20
想法,检查以第一行开头的交叉点<> lastline,firstline<> secondlastline ... firstline<> thirdline => secondline<> lastline etc这应该给你最外面的交叉点。
Idea, check for intersections beginning with firstline<>lastline, firstline<>secondlastline ... firstline<>thirdline => secondline<>lastline etc. This should give you the outer most intersection.
以下代码没有经过测试,但可以帮助解决你的问题。
The following Code is not tested, but should help you with your problem.
typedef struct {
CGPoint startPoint;
CGPoint endPoint;
} Line;
#define CGPointNULL CGPointMake(NAN, NAN)
#define Line(_i_) {CGPointFromString(touchPoints[_i_-1]), CGPointFromString(touchPoints[_i_])};
CGPoint LineIntersects(Line *first, Line *second) {
int x1 = first->startPoint.x; int y1 = first->startPoint.y;
int x2 = first->endPoint.x; int y2 = first->endPoint.y;
int x3 = second->startPoint.x; int y3 = second->startPoint.y;
int x4 = second->endPoint.x; int y4 = second->endPoint.y;
int d = (x1-x2)*(y3-y4) - (y1-y2)*(x3-x4);
if (d == 0) return CGPointNULL;
int xi = ((x3-x4)*(x1*y2-y1*x2)-(x1-x2)*(x3*y4-y3*x4))/d;
int yi = ((y3-y4)*(x1*y2-y1*x2)-(y1-y2)*(x3*y4-y3*x4))/d;
return CGPointMake(xi,yi);
}
static inline BOOL CGPointIsValid(CGPoint p) {
return (p.x != NAN && p.y != NAN);
}
- (CGPoint)mostOuterIntersection:(NSArray *)touchPoints {
CGPoint intersection = CGPointNULL;
int touchCount = [touchPoints count];
for(int i = 1; i<touchCount; i++) {
Line first = Line(i);
for(int j = touchCount-1; j>i+1; j--) {
Line last = Line(j);
intersection = LineIntersects(&first, &last);
if(CGPointIsValid(intersection)) {
break;
}
}
}
return intersection;
}