本文是在微信小程序中使用 canvas 2d 来实现签字板功能;
效果图:
代码:
1、wxml
<view><canvas id="canvas"type="2d"bindtouchstart="start"bindtouchmove="move"bindtouchend="end"style="border: 1px solid #ccc; width:100%; height:800rpx"></canvas><view style="display: flex;"><button bindtap="clear">清除</button><button bindtap="save">保存</button></view><image src="{{canvanImg}}"></image>
</view>
2、js
Component({properties: {},data: {canvas:null,canvanImg:"",ctx:null},lifetimes:{ready(){let that = this;wx.createSelectorQuery().in(this).select("#canvas").fields({node:true,size:true}).exec((res)=>{let canvas = res[0].node;let ctx = canvas.getContext("2d");let dpr = wx.getSystemInfoSync().pixelRatio;canvas.width = res[0].width * dpr;canvas.height = res[0].height * dpr;ctx.fillStyle = "#fff";// 利用阴影,消除锯齿ctx.shadowBlur = 1;ctx.shadowColor = '#000';ctx.scale(dpr, dpr)that.setData({canvas,ctx})})}},methods: {//触摸开始start (e) {this.data.ctx.beginPath()this.data.ctx.moveTo(e.touches[0].x,e.touches[0].y)},//触摸移动move (e) {this.data.ctx.lineTo(e.touches[0].x, e.touches[0].y)this.data.ctx.stroke()//将上下文绘制到canvas中},//触摸结束end (e) {this.data.ctx.closePath()},//清除画布内容clear(){this.data.ctx.clearRect(0, 0,this.data.canvas.width, this.data.canvas.height)this.setData({canvanImg:""})},//点击保存生成图片save(){this.setData({canvanImg:this.data.canvas.toDataURL("image/png")})},}
})
3、总结
canvas 的宽度和高度可以写死,也可以根据当前可是区域动态计算;需要注意的是 res[0].node 的宽度和高度的计算是当前 canvas 元素上的宽度和高度乘设备的 pixelRatio ;