判斷兩線段是否相交

BOOL IsHavePoint(Point ptsBegin, Point ptsEnd) { Point pFirst = GetPointOnPage(11,10); Point pSecond = GetPointOnPage(88,10); double k1,k2,b1,b2; k1 = (ptsEnd.Y-ptsBegin.Y)/(double)(ptsEnd.X-ptsBegin.X); b1 = (ptsBegin.X*ptsEnd.Y - ptsEnd.X*ptsBegin.Y)/(double)(ptsBegin.X-ptsEnd.X); k2 = (pSecond.Y-pFirst.Y)/(double)(pSecond.X-pFirst.X); b2 = (pFirst.X*pSecond.Y - pSecond.X*pFirst.Y)/(double)(pFirst.X-pSecond.X); if (k1 == k2) { return FALSE; } double x = (b2-b1)/(k1-k2); double x1 = (ptsBegin.X>ptsEnd.X)?(ptsEnd.X):(ptsBegin.X); double x2 = (ptsBegin.X>ptsEnd.X)?(ptsBegin.X):(ptsEnd.X); if (x>=x1&&x<=x2) { x1 = (pFirst.X>pSecond.X)?(pSecond.X):(pFirst.X); x2 = (pFirst.X>pSecond.X)?(pFirst.X):(pSecond.X); if (x>=x1&&x<=x2) return TRUE; } return FALSE; }

k=y2-y1/x2-x1

b=(x1*y2-x2*y1)(x1-x2)

用這個方法求出線段的直線公式，分別求出兩條線段的直線公式K1,K2,B1,B2

在根據 x = (b2-b1)/(k1-k2);求出X，x必須在四個點的中間。這樣就可以判斷其是否相交。

 

 

上面的方法沒有考慮X1=X2的情況和Y1=Y2的情況，會出現問題

IsCompare(Point Line1Begin,Point Line1End,Point Line2Begin,Point Line2End) { int x1 = Line1Begin.X; int y1 = Line1Begin.Y; int x2 = Line1End.X; int y2 = Line1End.Y; int x3 = Line2Begin.X; int y3 = Line2Begin.Y; int x4 = Line2End.X; int y4 = Line2End.Y; BOOL a,b; BOOL s=FALSE,d=FALSE; BOOL temp1=FALSE,temp2=FALSE; BOOL final1=FALSE,final2=FALSE; if( (x2-x1)*(y3-y1) - (y2-y1)*(x3-x1) == 0) { if((x3-x1)*(x3-x2)<=0 && (y3-y1)*(y3-y2)<=0) { final1=TRUE; temp1=TRUE; } else s=TRUE; } else if( (x2-x1)*(y3-y1) - (y2-y1)*(x3-x1) > 0 ) a=TRUE; else a=FALSE; if( (x2-x1)*(y4-y1) - (y2-y1)*(x4-x1) == 0) { if((x4-x1)*(x4-x2)<=0 && (y4-y1)*(y4-y2)<=0) { final1=TRUE; temp1=TRUE; } else s=TRUE; } else if( (x2-x1)*(y4-y1) - (y2-y1)*(x4-x1) > 0 ) b=TRUE; else b=FALSE; if(final1==TRUE) return TRUE; else { if(s==1) temp1=FALSE; else { if(a != b) temp1=TRUE; else temp1=FALSE; } if(temp1==FALSE) return FALSE; else { a=FALSE; b=FALSE; if( (x4-x3)*(y1-y3) - (y4-y3)*(x1-x3) == 0) { if((x1-x3)*(x1-x4)<=0 && (y1-y3)*(y1-y4)<=0) { final2=TRUE; temp2=TRUE; } else d=TRUE; } else if( (x4-x3)*(y1-y3) - (y4-y3)*(x1-x3) > 0 ) a=TRUE; else a=FALSE; if( (x4-x3)*(y2-y3) - (y4-y3)*(x2-x3) == 0) { if((x2-x3)*(x2-x4)<=0 && (y2-y3)*(y2-y4)<=0) { final2=TRUE; temp2=TRUE; } else d=TRUE; } else if((x4-x3)*(y2-y3) - (y4-y3)*(x2-x3) > 0) b=TRUE; else b=FALSE; if(final2==TRUE) return TRUE; else { if(d==1) temp2=FALSE; else { if(a != b) temp2=TRUE; else temp2=FALSE; } if(temp2==FALSE) return FALSE; else return TRUE; } } } }

 

另外一種方法是

inline double Multiply(Point p1, Point p2, Point p0) { return ( (p1.X-p0.X)*(p2.Y-p0.Y) - (p2.X-p0.X)*(p1.Y-p0.Y) ); } BOOL IsCompare(Point Line1Begin,Point Line1End,Point Line2Begin,Point Line2End) { int x1 = Line1Begin.X; int y1 = Line1Begin.Y; int x2 = Line1End.X; int y2 = Line1End.Y; int x3 = Line2Begin.X; int y3 = Line2Begin.Y; int x4 = Line2End.X; int y4 = Line2End.Y; return( (max(x1, x2) >= min(x3, x4)) && (max(x3, x4) >= min(x1, x2)) && (max(y1, y2) >= min(y3, y4)) && (max(y3, y4) >= min(y1, y2)) && (Multiply(Line2Begin, Line1End, Line1Begin) * Multiply(Line1End, Line2End, Line1Begin) >= 0) && (Multiply(Line1Begin, Line2End, Line2Begin) * Multiply(Line2End, Line1End, Line2Begin) >= 0) ); }