Calculate the intersection of two straight lines (C #)

The source code from other places is problematic.

/// <Summary> /// calculate the intersection of two straight lines /// </summary> /// <param name = "lineFirstStar"> coordinate 1 of L1 Points </param> /// <param name = "lineFirstEnd"> L1 coordinate 2 </param> /// <param name = "lineSecondStar"> L2 coordinate 1 </param> /// <param name = "lineSecondEnd"> L2 coordinate 2 </param> /// <returns> </returns> public static PointF GetIntersection (PointF lineFirstStar, pointF lineFirstEnd, PointF lineSecondStar, PointF lineSecondEnd) {/** L1, L2 all have slope * Linear equation L1: (y-y1)/(y2-y1) = (x-x1)/(x2-x1) * => y = [(y2-y1)/(x2-x1)] (x-x1) + y1 * Make a = (y2-y1)/(x2-x1) * y = a * x-a * x1 + y1 ......... 1 * linear equation L2: (y-y3)/(y4-y3) = (x-x3)/(x4-x3) * Order B = (y4-y3) /(x4-x3) * y = B * x-B * x3 + y3 .......... 2 ** if a = B, the two straight lines are equal. Otherwise, the equation 1, 2 is obtained: * x = (a * x1-B * x3-y1 + y3 ). )/(A-B) * y = a * x-a * x1 + y1 ** L1 has a slope and L2 parallel y axis: * x = x3 * y = a * x3-a * x1 + y1 ** L1 parallel y axis. L2 has a slope: * x = x1 * y = B * x-B * x3 + y3 ** when both L1 and L2 are parallel y axes: * If x1 = x3, L1 and L2 coincide, otherwise equal **/float a = 0, B = 0; int state = 0; if (lineFirstStar. x! = LineFirstEnd. X) {a = (lineFirstEnd. Y-lineFirstStar. Y)/(lineFirstEnd. X-lineFirstStar. X); state | = 1 ;}if (lineSecondStar. X! = LineSecondEnd. x) {B = (lineSecondEnd. y-lineSecondStar. y)/(lineSecondEnd. x-lineSecondStar. x); state | = 2;} switch (state) {case 0: // L1 and L2 are both parallel y axes {if (lineFirstStar. X = lineSecondStar. x) {// throw new Exception ("the two straight lines overlap with each other and are parallel to the Y axis. The intersection cannot be calculated. "); Return new PointF (0, 0);} else {// throw new Exception (" the two straight lines are parallel to each other and are parallel to the Y axis. The intersection cannot be calculated. "); Return new PointF (0, 0);} case 1: // L1 slope, L2 parallel Y axis {float x = lineSecondStar. x; float y = (lineFirstStar. x-x) * (-a) + lineFirstStar. y; return new PointF (x, y);} case 2: // L1 parallel Y axis, L2 has slope {float x = lineFirstStar. x; // similar code is found on the Internet, which is incorrect. You can compare the logic of case 1 for analysis // source code: lineSecondStar * x + lineSecondStar * lineSecondStar. X + p3.Y; float y = (lineSecondStar. x-x) * (-B) + lineSecondStar. y; return new PointF (x, y);} case 3: // L1, L2 all have slope {if (a = B) {// throw new Exception ("the intersection cannot be calculated because two straight lines are parallel or overlapped. "); Return new PointF (0, 0);} float x = (a * lineFirstStar. x-B * lineSecondStar. x-lineFirstStar. Y + lineSecondStar. y)/(a-B); float y = a * x-a * lineFirstStar. X + lineFirstStar. y; return new PointF (x, y) ;}// throw new Exception ("impossible situation"); return new PointF (0, 0 );}