【Unity|备忘】在脚本中动态设置ParentConstraint_parent constraints 头引用

【Unity|备忘】在脚本中动态设置ParentConstraint

功能本身很简单，就是计算初始的 Position offset 和 Rotation offset 时需要注意一下坐标系。示例代码：

public static ParentConstraint SetParentConstraint(Transform target, Transform parentSource,
    ParentConstraint constraint = null)
{
    Assert.IsTrue(!constraint || target == constraint.transform);

    if (!constraint)
    {
        if (!parentSource) return null;
        constraint = target.gameObject.AddComponent<ParentConstraint>();
    }

    // 清空已有约束
    constraint.constraintActive = false;
    for (int i = constraint.sourceCount - 1; i >= 0; i--)
    {
        constraint.RemoveSource(i);
    }

    // 无约束
    if (!parentSource) return constraint;

    // 设置新约束
    constraint.AddSource(new ConstraintSource
    {
        sourceTransform = parentSource,
        weight = 1,
    });

    // 设置 Position offset
    var positionOffset = parentSource.InverseTransformPoint(target.position);
    constraint.SetTranslationOffset(0, positionOffset);

    // 设置 Rotation offset
    var localForward = parentSource.InverseTransformDirection(target.forward);
    var localUpward = parentSource.InverseTransformDirection(target.up);
    var rotationOffset = Quaternion.LookRotation(localForward, localUpward).eulerAngles;
    constraint.SetRotationOffset(0, rotationOffset);

    // 激活约束
    constraint.constraintActive = true;

    return constraint;
}
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附带可能用到的坐标系转换方法：

/// <summary>
/// 局部坐标转世界坐标。
/// </summary>
/// <param name="localPosition">局部坐标系位置。</param>
/// <param name="localRotation">局部坐标系旋转。</param>
/// <param name="localCoordWorldPosition">局部坐标系原点在世界坐标系中的位置。</param>
/// <param name="localCoordWorldRotation">局部坐标系在世界坐标系中的旋转。</param>
/// <param name="worldPosition">转换后的世界坐标系位置。</param>
/// <param name="worldRotation">转换后的世界坐标系旋转。</param>
public static void LocalToWorld(Vector3 localPosition, Quaternion localRotation,
    Vector3 localCoordWorldPosition, Quaternion localCoordWorldRotation,
    out Vector3 worldPosition, out Quaternion worldRotation)
{
    var matrix = Matrix4x4.TRS(localCoordWorldPosition, localCoordWorldRotation, Vector3.one);
    worldPosition = matrix.MultiplyPoint(localPosition);
    worldRotation = matrix.rotation * localRotation;
    // scale = localScale;
    // scale.Scale(matrix.lossyScale);
}
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