Two lines intersection

intersect.cpp

LIB_INLINE BOOL32 CMath::MathRayIntersect ( POINT A1, POINT A2, POINT B1, POINT B2, POINT *lpResult )
{	
	INT dx1 = A2.x - A1.x;
	INT dy1 = A2.y - A1.y;
	INT dx2 = B2.x - B1.x;
	INT dy2 = B2.y - B1.y;
	
	DOUBLE q = (dx1 * dy2) - (dy1 * dx2);
	if (abs(q) < 0.0001) q = 0.0001;

	DOUBLE r = ((A1.y - B1.y) * dx2 - (A1.x - B1.x) * dy2) / q;
	
	lpResult->x = (INT) ( A1.x + r * dx1 );
	lpResult->y = (INT) ( A1.y + r * dy1 );

	dx1 = B2.x - B1.x;
	dy1 = B2.y - B1.y;
	dx2 = A2.x - A1.x;
	dy2 = A2.y - A1.y;

	q = (dx1 * dy2) - (dy1 * dx2);
	if (abs(q) < 0.0001) q = 0.0001;
	
	DOUBLE s = ((B1.y - A1.y) * dx2 - (B1.x - A1.x) * dy2) / q;
	
	return (r > 0 && r < 1 && s > 0 && s < 1);
}