PaperJS

Question

here中显示的示例展示了如何在 Paperjs 中沿路径移动对象，但如何沿路径正确旋转对象？

在上面link的例子中，大家建议以圆圈为例。但是一旦变成了一个矩形new Path.Rectangle(new Point(20,20), new Size(20,20));你可以看到它沿着路径移动但实际上并没有沿着路径的方向旋转

如何计算旋转并将其设置到我的对象？

Answer 1

为了计算旋转，您需要知道矩形位置路径的切向量。
这可以用 path.getTangentAt(offset) 方法检索。
然后，为项目旋转设置动画的简单方法是将 item.applyMatrix 设置为 false，然后在每一帧上为 item.rotation 属性设置动画。

这里是 sketch 演示解决方案。

// Create the rectangle to animate along the path.
// Note that matrix is not applied, this will allow us to easily animate its
// rotation.
var rectangle = new Path.Rectangle({
    point: view.center,
    size: new Size(100, 200),
    strokeColor: 'orange',
    applyMatrix: false
});

// Create the path along which the rectangle will be animated.
var path = new Path.Circle({
    center: view.center,
    radius: 250,
    strokeColor: 'blue'
});

// On each frame...
function onFrame(event) {
    // ...calculate the time of the animation between 0 and 1... 
    var slowness = 400;
    var time = event.count % slowness / slowness;
    // ...and move the rectangle.
    updateRectangle(time);
}

function updateRectangle(time) {
    // Calculate the offset relatively to the path length.
    var offset = time * path.length;
    // Get point to position the rectangle.
    var point = path.getPointAt(offset);
    // Get tangent vector at this point.
    var tangent = path.getTangentAt(offset);
    // Move rectangle.
    rectangle.position = point;
    // Rotate rectangle.
    rectangle.rotation = tangent.angle;
}

PaperJS - 如何沿路径移动并沿路径旋转

PaperJS - How to move along path and rotate along the path

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