StretchedBillboard 实现

参考Unity粒子系统的StretchedBillboard,在保持模型的右朝向不变的情况下,尽量朝向摄像机

转化为数学问题: 一个向量在一个面上的投影

基础的Billboard的方向应为: 从中点指向摄像机

限制的平面为以right为法向量的平面

算法

Vector3 rightward = transform.parent.forward;
if (isShowLeft) rightward = -rightward;
Vector3 forward = (Camera.current.transform.position - transform.position).normalized;
if (isShowBack) forward = -forward;

float cosVal = Vector3.Dot(rightward, forward);
if (Mathf.Abs(cosVal) >= 0.999999f) return;

rightward = rightward * cosVal;
forward = forward - rightward;

//不能用forward改变,不能保证right朝向 有时候会反过来
if (cosVal > 0)
transform.rotation = Quaternion.LookRotation(forward, Vector3.Cross(rightward, forward));
else
transform.rotation = Quaternion.LookRotation(forward, Vector3.Cross(forward, rightward));

//角度旋转
if (billboardAngle != 0)
{
Vector3 oriAngle = transform.eulerAngles;
oriAngle.x += billboardAngle;
transform.eulerAngles = oriAngle;
}

x

24

 

1

            Vector3 rightward = transform.parent.forward;

2

            if (isShowLeft) rightward = -rightward;

3

            Vector3 forward = (Camera.current.transform.position - transform.position).normalized;

4

            if (isShowBack) forward = -forward;

5

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            float cosVal = Vector3.Dot(rightward, forward);

7

            if (Mathf.Abs(cosVal) >= 0.999999f) return;

8

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            rightward = rightward * cosVal;

10

            forward = forward - rightward;

11

12

            //不能用forward改变,不能保证right朝向 有时候会反过来

13

            if (cosVal > 0)

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                transform.rotation = Quaternion.LookRotation(forward, Vector3.Cross(rightward, forward));

15

            else

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                transform.rotation = Quaternion.LookRotation(forward, Vector3.Cross(forward, rightward));

17

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            //角度旋转

19

            if (billboardAngle != 0)

20

            {

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                Vector3 oriAngle = transform.eulerAngles;

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                oriAngle.x += billboardAngle;

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                transform.eulerAngles = oriAngle;

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            }

效果: 白色为粒子系统的StretchedBillboard 红色为仿制的StretchedBillboard

 

最终计算朝向