gradient

A Gradient instance can be generated once or for every draw.

Examples:

Pre-configure the origin points and the _type_

    g = new Gradient(null, 'Linear', [stage.center])
    g.addStops({
        0: "hsl(299deg 62% 44%)",
        1: "hsl(244deg 71% 56%)"
    })

    let canvasGradient = g.getObject(ctx)
    ctx.fillStyle = canvasGradient

---

The context may be given early.

    g = new Gradient(ctx, 'Linear',)
    g.addStops({
        0: "hsl(299deg 62% 44%)",
        1: "hsl(244deg 71% 56%)"
    })
    let canvasGradient = g.getObject()
    ctx.fillStyle = canvasGradient

---

Provide the context at the last stage.

    g = new Gradient()
    g.addStops({
        0: "hsl(299deg 62% 44%)",
        1: "hsl(244deg 71% 56%)"
    })
    g = g.conical(stage.center)
    // draw
    ctx.fillStyle = g.getObject(ctx)

---

Radial gradient through two point. The same points are used as
color stops.

    pointGradInner = primaryPoint.copy().update({
            radius: rel(-250),
            color:'pink'
        })
    pointGradOuter = primaryPoint.copy().update({
            radius: rel(-10),
            color: 'purple' // dark
        })

    pointGrad = (new Gradient).radial(pointGradInner, pointGradOuter)
    pointGrad.addStops({
        0: pointGradInner,
        1: pointGradOuter
    })
    pointGrad.radial() // refresh hack.
    let ctxPointGrad = pointGrad.getObject(ctx)
    primaryPoint.pen.fill(ctx, ctxPointGrad)
---

This base `Gradient` class covers the three core types:

+ createConicGradient(startAngle, x, y)
+ createLinearGradient(x0, y0, x1, y1)
+ createRadialGradient(x0, y0, r0, x1, y1, r1)

## More Info

Create a new gradient object:

    let g = new Gradient()

Many _stops_ define the gradient color values. A _stop_ is a relative 1D
position from `0` to `1`.

    g.addStops({
        0: "hsl(299deg 62% 44%)",
        1: "hsl(244deg 71% 56%)"
    })

Define the type of gradient object:

    let rootPoint = stage.center
    let grad = g.linear(rootPoint)

Under the hood, this configures and refreshes `g` gradient instance. similar
to:

    // same as above
    g = new Gradient(null, 'Linear', [stage.center])

A canvas _gradient_ is generated when required. This Gradient class mimic
this:

    let canvasGradient = g.getObject(ctx)

The `getObject` method returns a result from the root functions, such as
`createLinearGradient`