StretchedBillboard 实现

Posted 2020-10-27 Hichy

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

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            Vector3 rightward = transform.parent.forward;

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            if (isShowLeft) rightward = -rightward;

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

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            if (isShowBack) forward = -forward;

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

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

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            rightward = rightward * cosVal;

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            forward = forward - rightward;

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

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            if (cosVal > 0)

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

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            else

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

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            //角度旋转

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            if (billboardAngle != 0)

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            {

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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