///
/// 只要線與矩形有一條線有相交，則線與矩形相交
///
public class LineWithRect : MonoBehaviour
{
public Rect rect = new Rect(0, 0, 100, 100);
public Transform LineStart;
public Transform lineEnd;

Vector3 VecLineStart;
Vector3 vecLineEnd;

Vector3 leftDown
{
    get
    {
        return new Vector2(rect.xMin, rect.yMin);
    }
}
Vector3 leftUp
{
    get
    {
        return new Vector2(rect.xMin, rect.yMax);
    }
}
Vector3 RigtDown
{
    get
    {
        return new Vector2(rect.xMax, rect.yMin);
    }
}
Vector3 RightUp
{
    get
    {
        return new Vector2(rect.xMax, rect.yMax);
    }
}

private void OnDrawGizmos()
{
    if (LineStart == null || lineEnd == null)
        return;

    VecLineStart = new Vector2(LineStart.position.x, LineStart.position.y);
    vecLineEnd = new Vector2(lineEnd.position.x, lineEnd.position.y);

    Gizmos.DrawLine(VecLineStart, vecLineEnd);

    Gizmos.DrawLine(leftDown, leftUp);
    Gizmos.DrawLine(leftUp, RightUp);
    Gizmos.DrawLine(RightUp, RigtDown);
    Gizmos.DrawLine(RigtDown, leftDown);
}

private void OnGUI()
{
    string content = "不在矩形內";
    if (LineInRect(VecLineStart, vecLineEnd, rect))
        content = "在矩形內";

    GUILayout.Label(content);

    content = "不相交";
    if (LineIntersectRect(VecLineStart, vecLineEnd, rect))
        content = "相交";

    GUILayout.Label(content);

    GUILayout.Label("RightUp:[" + RightUp + "]    RigtDown:[" + RigtDown);
}

// 線是否在矩形內
bool LineInRect(Vector2 lineStart, Vector2 lineEnd, Rect rect)
{
    return rect.Contains(lineStart) || rect.Contains(lineEnd);
}

// 線與矩形是否相交
bool LineIntersectRect(Vector2 lineStart, Vector2 lineEnd, Rect rect)
{
    if (LineIntersectLine(lineStart, lineEnd, leftDown, leftUp))
        return true;
    if (LineIntersectLine(lineStart, lineEnd, leftUp, RightUp))
        return true;
    if (LineIntersectLine(lineStart, lineEnd, RightUp, RigtDown))
        return true;
    if (LineIntersectLine(lineStart, lineEnd, RigtDown, leftDown))
        return true;

    return false;
}

// 線與線是否相交
bool LineIntersectLine(Vector2 l1Start, Vector2 l1End, Vector2 l2Start, Vector2 l2End)
{
    return QuickReject(l1Start, l1End, l2Start, l2End) && Straddle(l1Start, l1End, l2Start, l2End);
}

// 快速排序。  true=通過， false=不通過
bool QuickReject(Vector2 l1Start, Vector2 l1End, Vector2 l2Start, Vector2 l2End)
{
    float l1xMax = Mathf.Max(l1Start.x, l1End.x);
    float l1yMax = Mathf.Max(l1Start.y, l1End.y);
    float l1xMin = Mathf.Min(l1Start.x, l1End.x);
    float l1yMin = Mathf.Min(l1Start.y, l1End.y);

    float l2xMax = Mathf.Max(l2Start.x, l2End.x);
    float l2yMax = Mathf.Max(l2Start.y, l2End.y);
    float l2xMin = Mathf.Min(l2Start.x, l2End.x);
    float l2yMin = Mathf.Min(l2Start.y, l2End.y);

    if (l1xMax < l2xMin || l1yMax < l2yMin || l2xMax < l1xMin || l2yMax < l1yMin)
        return false;

    return true;
}

// 跨立實驗
bool Straddle(Vector3 l1Start, Vector3 l1End, Vector3 l2Start, Vector3 l2End)
{
    float l1x1 = l1Start.x;
    float l1x2 = l1End.x;
    float l1y1 = l1Start.y;
    float l1y2 = l1End.y;
    float l2x1 = l2Start.x;
    float l2x2 = l2End.x;
    float l2y1 = l2Start.y;
    float l2y2 = l2End.y;

    if ((((l1x1 - l2x1) * (l2y2 - l2y1) - (l1y1 - l2y1) * (l2x2 - l2x1)) *
         ((l1x2 - l2x1) * (l2y2 - l2y1) - (l1y2 - l2y1) * (l2x2 - l2x1))) > 0 ||
        (((l2x1 - l1x1) * (l1y2 - l1y1) - (l2y1 - l1y1) * (l1x2 - l1x1)) *
         ((l2x2 - l1x1) * (l1y2 - l1y1) - (l2y2 - l1y1) * (l1x2 - l1x1))) > 0)
    {
        return false;
    }

    return true;
}
 

}