---
title: Constructing the neck opening
sidebar_position: 60
---

Our goal is to construct an oval neck opening that has a circumference
that is the `head` measurements multiplied by the `neckRatio` option.

That might involve some trial and error. But since the neck opening will be symmetric
both horizontal and vertical, we only need to construct one quadrant.

## Destructuring measurements and options

We'll be adding some points to our pattern to do just that. But we want to have
access to our measurements and options to do so. For this, we first destructure
`measurements` and `options` so we can access them:

```design/src/bib.mjs
function draftBib({
  Path,
  Point,
  paths,
  points,
// highlight-start
  measurements,
  options,
// highlight-end
  part,
}) {

  return part
}
```

Great. Now let's get to work.

## Drawing our first path

Let's add some points, and use them to draw our first curve:

<Example tutorial caption="Our very first path forms a quarter of our neck opening">
```design/src/bib.mjs
function draftBib({
  Path,
  Point,
  paths,
  points,
  measurements,
  options,
  part,
}) {

// highlight-start
  /*
   * Construct the quarter neck opening
   */
  points.right = new Point(
    measurements.head / 10, 
    0
  )
  points.bottom = new Point(
    0, 
    measurements.head / 12
  )

  points.rightCp1 = points.right.shift(
    90, 
    points.bottom.dy(points.right) / 2
  )
  points.bottomCp2 = points.bottom.shift(
    0, 
    points.bottom.dx(points.right) / 2
  )

  paths.quarterNeck = new Path()
    .move(points.right)
    .curve(
      points.rightCp1, 
      points.bottomCp2, 
      points.bottom
    )
// highlight-end

  return part
}
```
</Example>

We've added some points to our part, and drawn our first path.
Let's look at each line in detail.

## Adding points

```js
points.right = new Point(
  measurements.head / 10, 
  0
)
```

- We're adding a point named `right` to the `points` object which holds our
  part's points
- We're using the Point constructor, which takes two arguments: The point's X
  and Y coordinates in the 2-dimensional space
- The X value is `measurements.head / 10`
- The Y value is `0`

The creation of `points.bottom` is very similar, so let's skip to the next line:

```js
points.rightCp1 = points.right.shift(
  90, 
  points.bottom.dy(points.right) / 2
)
```

- We're adding a point named `rightCp1`, which will become the _control point_
  of the right part
- Instead of using the Point constructor, we're calling the `Point.shift()`
  method on an existing point
- It takes two arguments: The angle to shift towards, and the distance
- We can see that we're shifting 90 degrees (that means up) but the distance
  uses another method
- The `Point.dy()` method returns the delta along the Y axis between the point
  we call it on and the point we pass it
- We shift half of the Y-delta

The next point is very similar again, except that this time we're shifting to
the right (0 degrees) for half of the X-delta between points `bottom` and
`right`.

:::tip
##### Further reading
The `Point.shift()` and `Point.dy()` are just the tip of the iceberg.
Points come with a bunch of these methods.
You can find them all in [the Point API docs](/reference/api/point/).
:::

## Adding paths

Adding points is typically merely a means to an end. And that end gets
introduced on the next line: Paths.

```js
paths.quarterNeck = new Path()
  .move(points.right)
  .curve(
    points.rightCp1, 
    points.bottomCp2, 
    points.bottom
  )
```

- We're adding a path named `quarterNeck` to the `paths` object which holds our
  part's paths
- We're using the Path constructor, which takes no arguments
- We're following up with a `Path.move()` call that takes one Point as argument
- Then, there's a `Path.curve()` call that takes 3 points as arguments

If you've read through the high-level [Design guide](/guides/designs) you
will have learned that paths always start with a `move()` operation. In this
case, we moved to our `right` points.

From there, we drew a cubic Bézier curve to our `bottom` point by using
`rightCp1` and `bottomCp2` as control points.

:::tip

Many of the methods in the FreeSewing API are *chainable* allowing you
to string them together like in this example.
:::

When all is said and done, we now have a quarter of our neck opening.
The only problem is, we have no guarantee whatsoever that this opening is the correct size.

Rather than hope it is the correct size, we'll make sure it is next.