一个贝塞尔曲线编辑工具(2d)

曲线在unity下如何绘制？

类似绘制圆，是用一段一段的线段拼接来模拟的，这边也是类似，可以用一段一段的线段来模拟曲线。

既然要模拟，那我们也得知道贝塞尔曲线的公式才行。

一般用的比较多的就是3次贝塞尔曲线，该曲线由起点p1，p1的控制点c1，终点p2，p2的控制点c2组成。

公式为：p = p1*(1-t)³ + 3*c1*t*(1-t)² + 3*c2*t²*(1-t) + p2*t³，t的范围[0, 1]

下面是unity下的一个贝塞尔编辑工具

public class MyBezierPath2dEdit : MonoBehaviour
{

    public string m_ControlInObjectName = "In"; //作为曲线结束时, c2控制点
    public string m_ControlOutObjectName = "Out"; //作为曲线启示点时, c1控制点
    public Color m_ControlInColor = Color.red; //c2控制点连线颜色
    public Color m_ControlOutColor = Color.blue; //c1点连线颜色

    public Color m_PathColor = Color.yellow; //路径绘制颜色

    [Range(1, 60)]
    public int m_Steps = 30; //曲线用多少个直线来模拟
    public bool m_LoopPath = false; //曲线是否首尾连接

    private void OnDrawGizmos()
    {
        var mainPoints = new List<Vector2>();
        var In = new List<Vector2>();
        var Out = new List<Vector2>();
        bool isAddRectTransform = null != GetComponent<RectTransform>();

        foreach (Transform child in transform)
        {
            mainPoints.Add(child.transform.position);
            foreach (Transform child2 in child.transform)
            {
                if (child2.name == m_ControlInObjectName)
                    In.Add(child2.transform.position);
                if (child2.name == m_ControlOutObjectName)
                    Out.Add(child2.transform.position);
            }

            //如果没有定义的点，则补充上去
            if (In.Count < mainPoints.Count)
            {
                GameObject go = new GameObject(m_ControlInObjectName);
                if (isAddRectTransform)
                    go.AddComponent<RectTransform>();
                go.transform.SetParent(child.transform, false);
                In.Add(go.transform.position);
            }
            if (Out.Count < mainPoints.Count)
            {
                GameObject go = new GameObject(m_ControlOutObjectName);
                if (isAddRectTransform)
                    go.AddComponent<RectTransform>();
                go.transform.SetParent(child.transform, false);
                Out.Add(go.transform.position);
            }
        }

        //曲线控制线
        for (int i = 0; i < mainPoints.Count; i++)
        {
            Gizmos.color = m_ControlInColor;
            Gizmos.DrawLine(mainPoints[i], In[i]);
            Gizmos.color = m_ControlOutColor;
            Gizmos.DrawLine(mainPoints[i], Out[i]);
        }

        Gizmos.color = m_PathColor;
        if (In.Count >= mainPoints.Count && Out.Count >= mainPoints.Count)
        {
            int mainPtCnt = mainPoints.Count;
            if (!m_LoopPath) mainPtCnt--;
            for (int i = 0; i < mainPtCnt; i++)
            {
                int i2 = (i + 1) % mainPoints.Count;
                Vector3 P2 = new Vector3(0, 0, 0);
                float step = 1.0f / m_Steps;
                if (step > 0.01f)
                {
                    for (float t = 0; t < 1 + step; t += step)
                    {
                        Vector3 P1 = P2;
                        P2 = CalcBezierPathPoint(mainPoints[i], Out[i], In[i2], mainPoints[i2], t);
                        if (t > 0)
                        {
                            Gizmos.DrawLine(P1, P2);
                        }
                    }
                }
            }
        }
    }

    private Vector3 CalcBezierPathPoint(Vector3 P0, Vector3 C0, Vector3 C1, Vector3 P1, float t)
    {
        float temp = 1 - t;
        Vector2 result = temp * temp * temp * P0 + 3 * temp * temp * t * C0 + 3 * temp * t * t * C1 + t * t * t * P1;
        return result;
    }

}