parabola.js

/*
 * A smart parabola for react-native apps
 * https://github.com/react-native-component/react-native-smart-parabola/
 * Released under the MIT license
 * Copyright (c) 2016 react-native-component <moonsunfall@aliyun.com>
 */

import React, {
    PropTypes,
    Component,
} from 'react'
import {
    StyleSheet,
    View,
    Text,
    Dimensions,
} from 'react-native'

export default class Parabola extends Component {

    static defaultProps = {
        rate: 1,
        duration: 500,
        top: 0,
    }

    static propTypes = {
        isTrigger: PropTypes.bool.isRequired, //true/false
        rate: PropTypes.number,
        start: PropTypes.shape({
            x: PropTypes.number.isRequired,
            y: PropTypes.number.isRequired,
        }).isRequired,
        end: PropTypes.shape({
            x: PropTypes.number.isRequired,
            y: PropTypes.number.isRequired,
        }).isRequired,
        duration: PropTypes.number,
        top: PropTypes.number,
        renderParabola: PropTypes.func.isRequired,
    }

    // 构造
    constructor (props) {
        super(props)
        // 初始状态
        this.state = {
            parabolas: [],
        }
        this._isAnimating = false
    }

    componentWillReceiveProps (nextProps) {
        let {start, end, isTrigger,} = nextProps
        if (isTrigger) {
            let parabola = {
                start,
                end,
                translateX: 0,
                translateY: 0,
                startTime: Date.now(),
                animationEnd: false,
            }
            this._addBall(parabola)
        }
    }

    render () {
        let parabolas = this.state.parabolas.map((parabola, index) => {
            let {translateX, translateY,} = parabola
            return this.props.renderParabola({
                index,
                translateX,
                translateY,
            })
        })
        return (
            <View style={{position: 'absolute', left: 0, top: 0}}>
                {parabolas}
            </View>
        )
    }

    _addBall (parabola) {
        this.state.parabolas.push(parabola)

        if(!this._isAnimating) {
            this._updateBalls()
        }
    }

    _updateBalls () {
        this._isAnimating = true

        if (this.state.parabolas.length == 0) {
            this._isAnimating = false
            return
        }

        let {duration, rate, top: rry1,} = this.props

        //let r_animationEnd //test code

        let parabolas = this.state.parabolas.map((parabola) => {

            let {start, end, startTime, animationEnd} = parabola

            let interval = Date.now() - startTime

            if (interval > duration) {
                if(animationEnd) {
                    return null
                }
                else {
                    interval = duration
                    parabola.animationEnd = true
                    //r_animationEnd = true //test code
                }
            }

            let percent = interval / duration

            let {x: rx1, y: ry1} = start
            let {x: rx2, y: ry2} = end

            let direction = rx2 > rx1 ? 1 : -1

            let lmy1 = ry2 - rry1
            let my1 = ry2 - ry1
            let mx2 = direction * (rx2 - rx1)
            let lmh = mx2 / 2
            //let mh = (1 - my1 / lmy1) * lmh
            let mh = (1 - my1 / lmy1) * lmh * ( rate ) * (1 - my1 / lmy1)  + lmh * ( 1 - rate) * (1 + my1 / lmy1)

            let a = my1 / mx2 / (2 * mh - mx2)
            let b = -2 * a * mh
            let c = my1

            let mx = percent * mx2
            let my = a * Math.pow(mx, 2) + b * mx + c

            parabola.translateX = rx1 + direction * mx
            parabola.translateY = ry2 - my

            return parabola
        })

        parabolas = parabolas.filter((parabola) => {
            return parabola != null
        })

        this.setState({
            parabolas,
        })

        //if(!r_animationEnd)   //test code
        requestAnimationFrame(this._updateBalls.bind(this))
    }

}