当我“绘制”线条时，如何将点平均分配到 LineRenderer 的宽度曲线？

我正在使用线条渲染器创建一个“绘图”应用程序，现在我尝试使用线条渲染器上的宽度曲线启用笔压。问题在于，AnimationCurve 的“时间”值（水平轴）从 0 标准化为 1，因此我不能在每次添加位置时都在其末尾添加一个值。除非有一个我不知道的函数，否则我能想到的唯一解决方案就是找到一种方法，在绘制线条时将所有数百个先前值移动精确的百分比，并在添加位置时执行此操作。这似乎太过分了。

我不知道在这里做什么。

这是我用笔绘制时在每一帧添加点的基本线。

curve.AddKey(1.0f, penPressureValue);

“1.0f”是曲线上的位置（1 是最后一个），所以这只是在每帧的末尾添加一个点，在我绘制时改变整条线的宽度。

不幸的是，我认为没有一种方法可以实现这一点，这在某种程度上是不可思议的并且性能密集。

当然你可以计算它（假设LineRenderer从位置计数 = 0 开始），例如

public LineRenderer line;
private int positionCount;
private float totalLengthOld;

private void AddPoint(Vector3 position, float width)
{
    // increase the position count by one
    positionCount++;

    // set the count back to the line
    line.positionCount = positionCount;

    // add our new point
    line.SetPosition(positionCount - 1, position);

    // now get the current width curve
    var curve = line.widthCurve;

    // Is this the beginning of the line?
    if (positionCount == 1)
    {
        // First point => simply set the first keyframe 
        curve.MoveKey(0, new Keyframe(0f, width));
    }
    else
    {
        // otherwise get all positions
        var positions = new Vector3[positionCount];
        line.GetPositions(positions);

        // sum up the distances between positions to obtain the length of the line
        var totalLengthNew = 0f;
        for (var i = 1; i < positionCount; i++)
        {
            totalLengthNew += Vector3.Distance(positions[i - 1], positions[i]);
        }

        // calculate the time factor we have to apply to all already existing keyframes
        var factor = totalLengthOld / totalLengthNew;

        // then store for the next added point
        totalLengthOld = totalLengthNew;

        // now move all existing keys which are currently based on the totalLengthOld to according positions based on the totalLengthNew
        // we can skip the first one as it will stay at 0 always
        var keys = curve.keys;
        for (var i = 1; i < keys.Length; i++)
        {
            var key = keys[i];
            key.time *= factor;

            curve.MoveKey(i, key);
        }

        // add the new last keyframe
        curve.AddKey(1f, width);
    }

    // finally write the curve back to the line
    line.widthCurve = curve;
}

就像一个小演示一样

public class Example : MonoBehaviour
{
    public LineRenderer line;
    public Transform pen;
    [Range(0.01f, 0.5f)] public float width;
    public float drawThreshold = 0.1f;

    private int positionCount;
    private float totalLengthOld;
    private Vector3 lastPenPosition;
    
    private void Awake()
    {
        line = GetComponent<LineRenderer>();
        line.useWorldSpace = true;
        line.positionCount = 0;

        lastPenPosition = pen.position;
    }

    private void Update()
    {
        // just for the demo simply ping-pong the width over time
        width = Mathf.Lerp(0.01f, 0.8f, Mathf.PingPong(Time.time, 1f));

        var currentPenPosition = pen.position;
        
        if (Vector3.Distance(lastPenPosition, currentPenPosition) >= drawThreshold)
        {
            lastPenPosition = currentPenPosition;
            AddPoint(currentPenPosition, width);
        }
    }
    
    private void AddPoint(Vector3 position, float width)
    {
        positionCount++;

        line.positionCount = positionCount;
        line.SetPosition(positionCount - 1, position);

        var curve = line.widthCurve;

        if (positionCount == 1)
        {
            curve.MoveKey(0, new Keyframe(0f, width));
        }
        else
        {
            var positions = new Vector3[positionCount];
            line.GetPositions(positions);

            var totalLengthNew = 0f;
            for (var i = 1; i < positionCount; i++)
            {
                totalLengthNew += Vector3.Distance(positions[i - 1], positions[i]);
            }

            var factor = totalLengthOld / totalLengthNew;

            totalLengthOld = totalLengthNew;

            var keys = curve.keys;
            for (var i = 1; i < keys.Length; i++)
            {
                var key = keys[i];
                key.time *= factor;

                curve.MoveKey(i, key);
            }

            curve.AddKey(1f, width);
        }

        line.widthCurve = curve;
    }
}

当然，在达到一定数量的点后，这会达到性能极限。但我认为这是您目前可以使用的LineRenderer。否则LineRenderer可能只是不是正确的绘图工具。

当然，您可以采取一些技巧，在一定数量的点之后，使用以下方法将现有线烘焙成单独的固定网格LineRenderer.BakeMesh https://docs.unity3d.com/ScriptReference/LineRenderer.BakeMesh.html并开始一条新的线，仅将最后一个点作为起点。

这样，只有线条尚未烘焙的部分实际上会受到宽度曲线键移动的影响。

有点像例如

public int meshBakeThreshold = 50;

private void AddPoint(Vector3 position, float width)
{
    ......

    if (positionCount >= meshBakeThreshold)
    {
        CreateSnapShotAndStartOver(position, width);
    }
}

private void CreateSnapShotAndStartOver(Vector3 position, float width)
{
    // create a new GameObject that will receive the line snapsho mesh
    var snapshotObject = new GameObject("LineSnapshot", typeof(MeshRenderer), typeof(MeshFilter));

    // set the material
    var renderer = snapshotObject.GetComponent<Renderer>();
    renderer.material = line.material;

    // bake and set the mesh
    var meshFilter = snapshotObject.GetComponent<MeshFilter>();
    var mesh = new Mesh();
    line.BakeMesh(mesh, Camera.main, true);
    meshFilter.mesh = mesh;

    // start with a new line at the same current position
    positionCount = 0;
    AddPoint(position, width);
}

你必须稍微调整一下阈值，50可能有点低，只是用于演示。您希望在迭代所有关键帧和烘焙网格的性能成本之间找到平衡点；）