jff-canvas

View framework for HTML canvas

Basics

Adding a simple view

const canvas = new Canvas('canvas')

const view = new View({ x: 10, y: 10, width: 50, height: 50 })
view.backgroundColor = 'red'
canvas.rootview.addSubview(view)

Custom view

class CustomView extends View {
    constructor(frame) {
        super(frame)
    }

    viewDidAppear() {
        console.log('viewDidAppear')
    }
    viewDidDisappear() {
        console.log('viewDidDisappear')
    }  
    paint(canvas) {
        console.log('paint')
    }
}

Rendering

Basic stuff like background-color, stroke-color is rendered by default. More complex stuff can be handled manually in the paint(canvas) function. The canvas parameter is the Canvas object the view is inside of. The Canvas object as a ctx field which is the 2d-context of the canvas which can be used for full control over the rendering of the view.

class CustomView extends View {
    constructor(frame) {
        super(frame)
    }
    paint(canvas) {
        canvas.paintRect(this.frame.x + 10, this.frame.y + 10, this.frame.width - 20, this.frame.height - 20, 'red')

        canvas.ctx.beginPath()
        ...
    }
}

Event handling

The onMousedown(event) function is called whenever a click is registered on the view. The event parameter is a normal javascript mouse-event with a point attribute added, which contains the x and y coordinates of the event inside the view.

A function can be returned which is then called when the mouse moves and the button is still clicked. The last time the function is called is on the mouseup event. delta and moveDelta attributes are added to the event in htis case to show the total moved delta since mousedown and the delta since the last mousemove event.

Event.preventDefault() can still be used if the onMousedown function should not be triggered on no other views after this view has process the click.

The views are processed depth-first and only considered if the event is inside all parent-frames.

class CustomView extends View {
    constructor(frame) {
        super(frame)
    }
    onMousedown(downEvent) {
        console.log('mouse down on ', downEvent.point)

        return (moveEvent, mouseUp) => {
            if (!mouseUp) {
                console.log('mouse moved ', moveEvent.delta)
            } else {
                console.log('mouse up ', moveEvent.delta)
            }
        }
    }
}

Animations

A animate function is available on all View-objects. The signature is animate(duration, animation, onComplete, loop, easing). The duration is the total-duration in ms of the animation. animation: a function that take a progress parameter that goes from 0 -> 1. onComplete: function that is called once the animation has run the full duration and animation function been called with a 1. loop: boolean wheter the animation should loop or not. easing: a function that take a value 0 -> 1 and returns a value that should be passed instead to animation.

View.stopAnimation can be used to stop a ongoing animation.

const canvas = new Canvas('canvas')

const view = new View({ x: 10, y: 10, width: 50, height: 50 })
view.backgroundColor = 'red'
canvas.rootview.addSubview(view)

view.animate(500, p => {
    view.frame.x = 10 + 100 * p
}, () => {
    console.log('complete')
}, false, Ease.EaseOut)

The animation-parameter can be used together with the paint to enable advanced animations.