// Returns true if the lines between v0v1 and t0t1 cross// If the lines cross, the intersection between them will// be stored in intersectionPointbool linesCross(b2Vec2 v0, b2Vec2 v1, b2Vec2 t0, b2Vec2 t1, b2Vec2 &intersectionPoint){ if ( areVecsEqual(v1,t0) || areVecsEqual(v0,t0) || areVecsEqual(v1,t1) || areVecsEqual(v0,t1) ) return false; b2Vec2 vnormal = v1 - v0; vnormal = b2Cross(1.0f, vnormal); float v0d = b2Dot(vnormal, v0); float t0d = b2Dot(vnormal, t0); float t1d = b2Dot(vnormal, t1); if ( t0d > v0d && t1d > v0d ) return false; if ( t0d < v0d && t1d < v0d ) return false; b2Vec2 tnormal = t1 - t0; tnormal = b2Cross(1.0f, tnormal); t0d = b2Dot(tnormal, t0); v0d = b2Dot(tnormal, v0); float v1d = b2Dot(tnormal, v1); if ( v0d > t0d && v1d > t0d ) return false; if ( v0d < t0d && v1d < t0d ) return false; intersectionPoint = v0 + ((t0d-v0d)/(v1d-v0d)) * (v1-v0); return true;}
bool areVecsEqual(b2Vec2 v1, b2Vec2 v2) { return v1.x == v2.x && v1.y == v2.y;}struct pos{ double x ; double y ;};struct line{ pos st ; pos end ;};int n ;double Multiply(pos p1, pos p2, pos p0){ return ( (p1.x - p0.x) * (p2.y - p0.y) - (p2.x - p0.x) * (p1.y - p0.y) );}bool iscross(line L1, line L2){ return( (max(L1.st.x, L1.end.x) >= min(L2.st.x, L2.end.x)) && (max(L2.st.x, L2.end.x) >= min(L1.st.x, L1.end.x)) && (max(L1.st.y, L1.end.y) >= min(L2.st.y, L2.end.y)) && (max(L2.st.y, L2.end.y) >= min(L1.st.y, L1.end.y)) && (Multiply(L2.st, L1.end, L1.st) * Multiply(L1.end, L2.end, L1.st) >= 0) && (Multiply(L1.st, L2.end, L2.st) * Multiply(L2.end, L1.end, L2.st) >= 0) );}
