# class HexaPDF::Content::GraphicObject::Arc

Parent Object HexaPDF::Utils::MathHelpers

This class describes an elliptical arc in center parameterization that is approximated using Bezier curves. It can be used to draw circles, circular arcs, ellipses and elliptical arcs, all either in clockwise or counterclockwise direction and optionally inclined in respect to the x-axis.

This graphic object is registered under the :arc key for use with the `HexaPDF::Content::Canvas` class.

Examples:

```arc = canvas.graphic_object(:arc, a: 100, b: 50, end_angle: 150)
canvas.draw(arc).stroke
``` ### Attributes

a[R]

Length of semi-major axis which (without altering the `inclination`) is parallel to the x-axis

Examples:

```arc = canvas.graphic_object(:arc, a: 30, b: 30)
canvas.draw(arc).stroke
canvas.stroke_color("red").draw(arc, a: 60).stroke
``` b[R]

Length of semi-minor axis which (without altering the `inclination`) is parallel to the y-axis

Examples:

```arc = canvas.graphic_object(:arc, a: 30, b: 30)
canvas.draw(arc).stroke
canvas.stroke_color("red").draw(arc, b: 60).stroke
``` clockwise[R]

Direction of arc - if `true` in clockwise direction, else in counterclockwise direction

This is needed when filling paths using the nonzero winding number rule to achieve different effects.

Examples:

```arc = canvas.graphic_object(:arc, a: 40, b: 40)
canvas.draw(arc, cx: -50).draw(arc, cx: 50).
draw(arc, cx: -50, b: 80).
draw(arc, cx: 50, b: 80, clockwise: true).
fill(:nonzero)
``` cx[R]

x-coordinate of center point

Examples:

```arc = canvas.graphic_object(:arc, a: 30, b: 20)
canvas.draw(arc).stroke
canvas.stroke_color("red").draw(arc, cx: -50).stroke
``` cy[R]

y-coordinate of center point

Examples:

```arc = canvas.graphic_object(:arc, a: 30, b: 20)
canvas.draw(arc).stroke
canvas.stroke_color("red").draw(arc, cy: 50).stroke
``` end_angle[R]

End angle of the arc in degrees

Examples:

```arc = canvas.graphic_object(:arc, a: 30, b: 30)
canvas.draw(arc, end_angle: 160).stroke
``` inclination[R]

Inclination in degrees of the semi-major axis with respect to the x-axis

Examples:

```arc = canvas.graphic_object(:arc, a: 60, b: 30)
canvas.draw(arc, inclination: 45).stroke
``` max_curves[RW]

The maximal number of curves used for approximating a complete ellipse.

The higher the value the better the approximation will be but it will also take longer to compute. The value should not be lower than 4. Default value is 6 which already provides a good approximation.

Examples:

```arc = canvas.graphic_object(:arc, cx: -50, a: 40, b: 40)
arc.max_curves = 2
canvas.draw(arc)
arc.max_curves = 10
canvas.draw(arc, cx: 50)
canvas.stroke
``` start_angle[R]

Start angle of the arc in degrees

Examples:

```arc = canvas.graphic_object(:arc, a: 30, b: 30)
canvas.draw(arc, start_angle: 45).stroke
``` ### Public Class Methods

configure(**kwargs)

Creates and configures a new elliptical arc object.

See `configure` for the allowed keyword arguments.

new()

Creates an elliptical arc with default values (a counterclockwise unit circle at the origin).

Examples:

```canvas.draw(:arc).stroke
``` ### Public Instance Methods

configure(cx: nil, cy: nil, a: nil, b: nil, start_angle: nil, end_angle: nil, inclination: nil, clockwise: nil)

Configures the arc with

• center point (`cx`, `cy`),

• semi-major axis `a`,

• semi-minor axis `b`,

• start angle of `start_angle` degrees,

• end angle of `end_angle` degrees and

• an inclination in respect to the x-axis of `inclination` degrees.

The `clockwise` argument determines if the arc is drawn in the counterclockwise direction (`false`) or in the clockwise direction (`true`).

Any arguments not specified are not modified and retain their old value, see initialize for the inital values.

Returns self.

curves()

Returns an array of arrays that contain the points for the Bezier curves which are used for approximating the elliptical arc between `start_point` and `end_point`.

One subarray consists of

```[end_point_x, end_point_y, p1: control_point_1, p2: control_point_2]
```

The first start point is the one returned by `start_point`, the other start points are the end points of the curve before.

The format of the subarray is chosen so that it can be fed to the `Canvas#curve_to` method by using array splatting.

See: ELL s3.4.1 (especially the last box on page 18)

draw(canvas, move_to_start: true)

Draws the arc on the given `Canvas`.

If the argument `move_to_start` is `true`, a `Canvas#move_to` operation is executed to move the current point to the start point of the arc. Otherwise it is assumed that the current point already coincides with the start point

The `max_curves` value, if not already changed, is set to the value of the configuration option 'graphic_object.arc.max_curves' before drawing.

end_point()

Returns the end point of the elliptical arc.

Examples:

```arc = canvas.graphic_object(:arc, a: 40, b: 30, end_angle: 245)
canvas.draw(arc).stroke
canvas.fill_color("red").circle(*arc.end_point, 2).fill
``` point_at(angle)

Returns the point at `angle` degrees on the ellipse.

Note that the point may not lie on the arc itself!

start_point()

Returns the start point of the elliptical arc.

Examples:

```arc = canvas.graphic_object(:arc, a: 40, b: 30, start_angle: 60)
canvas.draw(arc).stroke
canvas.fill_color("red").circle(*arc.start_point, 2).fill
``` 