点击按钮，按钮以及按钮后的背景消失，开始绘制canvas
调用drawImage绘制上面的图片，当用户点击、移动时clearRect，在调试工具和iphone上都还可以，但是在安卓上面卡顿特别严重，而且页面会滚动，导致canvas区域移位，下面底层隐藏的图片直接出来了。安卓、ios手指移动时，清除滞后很明显。
class Scratch {
/**
* @constructs Scratch构造函数
* @param {Object} pageContext page路由指针
* @param {Object} opts 组件所需参数
* @param {Number} opts.canvasWidth 画布宽带
* @param {Number} opts.canvasHeight 画布高度
* @param {String} opts.imageResource 遮罩层图片
* @param {Number} opts.r 笔触半径
* @param {String} opts.awardTxt 底部抽奖文字奖项
* @param {String} opts.awardTxtColor 底部抽奖文字颜色
* @param {String} opts.awardTxtFontSize 底部抽奖文字大小
* @param {String} opts.maskColor 没有图片遮罩层颜色
* @param {Function} opts.callback 结束回调
*/
constructor (pageContext, opts) {
this.page = pageContext
this.canvasWidth = opts.canvasWidth
this.canvasHeight = opts.canvasHeight
this.imageResource = opts.imageResource
this.maskColor = opts.maskColor
// this.canvasId = opts.canvasId
this.r = opts.r || 4
this.endCallBack = opts.callback
this.lastX = 0
this.lastY = 0
this.minX = ‘’
this.minY = ‘’
this.maxX = ‘’
this.maxY = ‘’
this.isStart = false
this.init()
this.page.touchStart = this.touchStart.bind(this)
this.page.touchMove = this.touchMove.bind(this)
this.page.touchEnd = this.touchEnd.bind(this)
this.page.imgOnLoad = this.imgOnLoad.bind(this)
this.page.setData({
scratch: {
‘awardTxt’: opts.awardTxt,
‘awardTxtColor’: opts.awardTxtColor,
‘awardTxtFontSize’: opts.awardTxtFontSize,
‘awardTxtLineHeight’: opts.canvasHeight,
‘width’: opts.canvasWidth,
‘height’: opts.canvasHeight,
‘imageResource’: opts.imageResource
},
‘isScroll’: true
})
}
init () {
const { canvasWidth, canvasHeight, imageResource, maskColor } = this
const self = this
this.ctx = wx.createCanvasContext(‘scratch’)
this.ctx.clearRect(0, 0, canvasWidth, canvasHeight)
console.log(canvasWidth+’ == '+ canvasHeight)
if (imageResource && imageResource != ‘’) {
wx.downloadFile({
url: imageResource,
success: res => {
self.ctx.drawImage(res.tempFilePath, 0, 0, canvasWidth, canvasHeight)
self.ctx.draw()
}
})
} else {
self.ctx.setFillStyle(maskColor)
self.ctx.fillRect(0, 0, canvasWidth, canvasHeight)
self.ctx.draw()
}
}
drawRect (x, y) {
const { r, minX, minY, maxX, maxY } = this
const x1 = x - r > 0 ? x - r : 0
const y1 = y - r > 0 ? y - r : 0
if (’’ != minX) {
this.minX = minX > x1 ? x1 : minX
this.minY = minY > y1 ? y1 : minY
this.maxX = maxX > x1 ? maxX : x1
this.maxY = maxY > y1 ? maxY : y1
} else {
this.minX = x1
this.minY = y1
this.maxX = x1
this.maxY = y1
}
this.lastX = x1
this.lastY = y1
return [x1, y1, 2 * r]
}
start () {
console.log(‘start’)
this.isStart = true
this.page.setData({
‘isScroll’: false
})
}
restart () {
this.init()
this.lastX = 0
this.lastY = 0
this.minX = ‘’
this.minY = ‘’
this.maxX = ‘’
this.maxY = ‘’
this.isStart = true
this.page.setData({
‘isScroll’: false
})
}
touchStart (e) {
if (!this.isStart) return
const pos = this.drawRect(e.touches[0].x, e.touches[0].y)
// this.ctx.clearRect(pos[0], pos[1], pos[2], pos[2])
this.clearArcFun(pos[0], pos[1], 10, this.ctx)
this.ctx.draw(true)
}
touchMove (e) {
if (!this.isStart) return
const pos = this.drawRect(e.touches[0].x, e.touches[0].y)
// this.ctx.clearRect(pos[0], pos[1], pos[2], pos[2])
this.clearArcFun(pos[0], pos[1], 20, this.ctx)
this.ctx.draw(true)
}
touchEnd (e) {
if (!this.isStart) return
// 自动清楚采用点范围值方式判断
const { canvasWidth, canvasHeight, minX, minY, maxX, maxY } = this
if (maxX - minX > .6 * canvasWidth && maxY - minY > .6 * canvasHeight) {
this.ctx.draw()
this.endCallBack && this.endCallBack()
this.isStart = false
this.page.setData({
‘isScroll’: true
})
}
}
reset () {
this.init()
}
clearArcFun(x, y, r, ctx) {
var stepClear = 0.1;//这是定义精度
clearArc(x, y, r);
function clearArc(x, y, radius) {
var calcWidth = radius - stepClear;
var calcHeight = Math.sqrt(radius * radius - calcWidth * calcWidth);
var posX = x - calcWidth;
var posY = y - calcHeight;
var widthX = 2 * calcWidth;
var heightY = 2 * calcHeight;
if (stepClear <= radius) {
ctx.clearRect(posX, posY, widthX, heightY);
stepClear += 0.1;
clearArc(x, y, radius);
}
}
}
}
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