Conversion from quaternion to euler?

[nopjia]

Is there a way to go from quaternion to euler? (Similar to when you read from Quaternion.eulerAngles.)

There are plenty of methods on the quaternion to produce a quaternion from euler angles of various rotation orders, but not the other way around.

[unpacklo]

There currently isn't, but it's on the list of things to add. We have some code internally at Unity which requires this so we have a few implementations already, it's just a matter of verifying its numerical quality and adding tests to ensure it works the way we expect.

[WaynGames]

Implementation taken from wikipedia and ported to c#, for those who need :

using Unity.Mathematics;

public static class QuaternionExtensions
{
    public static float ComputeXAngle(this quaternion q)
    {
        float sinr_cosp = 2 * (q.value.w * q.value.x + q.value.y * q.value.z);
        float cosr_cosp = 1 - 2 * (q.value.x * q.value.x + q.value.y * q.value.y);
        return math.atan2(sinr_cosp, cosr_cosp);
    }

    public static float ComputeYAngle(this quaternion q)
    {
        float sinp = 2 * (q.value.w * q.value.y - q.value.z * q.value.x);
        if (math.abs(sinp) >= 1)
            return math.PI / 2 * math.sign(sinp); // use 90 degrees if out of range
        else
            return math.asin(sinp);
    }

    public static float ComputeZAngle(this quaternion q)
    {
        float siny_cosp = 2 * (q.value.w * q.value.z + q.value.x * q.value.y);
        float cosy_cosp = 1 - 2 * (q.value.y * q.value.y + q.value.z * q.value.z);
        return math.atan2(siny_cosp, cosy_cosp);
    }

    public static float3 CoputeAngles(this quaternion q)
    {
        return new float3(ComputeXAngle(q), ComputeYAngle(q), ComputeZAngle(q));
    }

    public static quaternion FromAngles(float3 angles)
    {

        float cy = math.cos(angles.z * 0.5f);
        float sy = math.sin(angles.z * 0.5f);
        float cp = math.cos(angles.y * 0.5f);
        float sp = math.sin(angles.y * 0.5f);
        float cr = math.cos(angles.x * 0.5f);
        float sr = math.sin(angles.x * 0.5f);

        float4 q;
        q.w = cr * cp * cy + sr * sp * sy;
        q.x = sr * cp * cy - cr * sp * sy;
        q.y = cr * sp * cy + sr * cp * sy;
        q.z = cr * cp * sy - sr * sp * cy;

        return q;

    }
}

[jimchan3301]

Someone mentioned that this function is in the Unity.Physics package: https://forum.unity.com/threads/is-there-a-conversion-method-from-quaternion-to-euler.624007/#post-6329286. This link is a discussion about how to convert from quaternions to Euler angles.