canvas
<canvas> 标签是 html 5 中的新标签。 <canvas> 标签只是图形容器，您必须使用脚本来绘制图形。canvas标签本身是没有绘图能力的，所有的绘制工作必须在 JavaScript 内部完成。
使用canvas绘图有几个必要的步骤：
- 获取canvas元素
- 通过canvas元素创建context对象
- 通过context对象来绘制图形
在当前电子签名需求中，由于签名其实是由一条条线组成的，因此我们会用到以下几个方法：
- beginPath() ：开始一条路径或重置当前的路径
- moveTo()：把路径移动到画布中的指定点，不创建线条
- lineTo()：添加一个新点，然后在画布中创建从该点到最后指定点的线条
- stroke()：绘制已定义的路径
- closePath()：创建从当前点回到起始点的路径
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事件
想要在canvas中绘图，还需要绑定几个特定的事件，而这些事件在pc端和手机端不尽相同
pc端事件
- mousedown
- mousemove
- mouseup
手机端事件
- touchstart
- touchmove
- touchend
核心代码
初始化canvas标签并绑定事件
<canvas @touchstart="touchStart" @touchmove="touchMove" @touchend="touchEnd" ref="canvasF" @mousedown="mouseDown" @mousemove="mouseMove" @mouseup="mouseUp" ></canvas>获取画笔
在mounted生命周期初始化
mounted() {
let canvas = this.$refs.canvasF; canvas.height = this.$refs.canvasHW.offsetHeight - 100; canvas.width = this.$refs.canvasHW.offsetWidth - 10; this.canvasTxt = canvas.getContext("2d"); this.canvasTxt.strokeStyle = this.color; this.canvasTxt.lineWidth = this.linewidth; }事件处理
mouseDown
//电脑设备事件 mouseDown(ev) { ev = ev || event; ev.preventDefault(); let obj = { x: ev.offsetX, y: ev.offsetY }; this.startX = obj.x; this.startY = obj.y; this.canvasTxt.beginPath();//开始作画 this.points.push(obj);//记录点 this.isDown = true; },touchStart
//移动设备事件 touchStart(ev) { ev = ev || event; ev.preventDefault(); if (ev.touches.length == 1) { this.isDraw = true; //签名标记 let obj = { x: ev.targetTouches[0].clientX, y: ev.targetTouches[0].clientY - (document.body.offsetHeight * 0.5 + this.$refs.canvasHW.offsetHeight * 0.1) }; //y的计算值中：document.body.offsetHeight*0.5代表的是除了整个画板signatureBox剩余的高，this.$refs.canvasHW.offsetHeight*0.1是画板中标题的高 this.startX = obj.x; this.startY = obj.y; this.canvasTxt.beginPath();//开始作画 this.points.push(obj);//记录点 } },mouseMove
//电脑设备事件 mouseMove(ev) { ev = ev || event; ev.preventDefault(); if (this.isDown) { let obj = { x: ev.offsetX, y: ev.offsetY }; this.moveY = obj.y; this.moveX = obj.x; this.canvasTxt.moveTo(this.startX, this.startY);//移动画笔 this.canvasTxt.lineTo(obj.x, obj.y);//创建线条 this.canvasTxt.stroke();//画线 this.startY = obj.y; this.startX = obj.x; this.points.push(obj);//记录点 } },touchMove
//移动设备事件 touchMove(ev) { ev = ev || event; ev.preventDefault(); if (ev.touches.length == 1) { let obj = { x: ev.targetTouches[0].clientX, y: ev.targetTouches[0].clientY - (document.body.offsetHeight * 0.5 + this.$refs.canvasHW.offsetHeight * 0.1) }; this.moveY = obj.y; this.moveX = obj.x; this.canvasTxt.moveTo(this.startX, this.startY);//移动画笔 this.canvasTxt.lineTo(obj.x, obj.y);//创建线条 this.canvasTxt.stroke();//画线 this.startY = obj.y; this.startX = obj.x; this.points.push(obj);//记录点 } },mouseUp
//电脑设备事件 mouseUp(ev) { ev = ev || event; ev.preventDefault(); if (1) { let obj = { x: ev.offsetX, y: ev.offsetY }; this.canvasTxt.closePath();//收笔 this.points.push(obj);//记录点 this.points.push({ x: -1, y: -1 }); this.isDown = false; } },touchEnd
//移动设备事件 touchEnd(ev) { ev = ev || event; ev.preventDefault(); if (ev.touches.length == 1) { let obj = { x: ev.targetTouches[0].clientX, y: ev.targetTouches[0].clientY - (document.body.offsetHeight * 0.5 + this.$refs.canvasHW.offsetHeight * 0.1) }; this.canvasTxt.closePath();//收笔 this.points.push(obj);//记录点 this.points.push({ x: -1, y: -1 });//记录点 } },重写
发现自己写错字了，擦掉画板重新写过
//重写 overwrite() { this.canvasTxt.clearRect( 0, 0, this.$refs.canvasF.width, this.$refs.canvasF.height ); this.points = []; this.isDraw = false; //签名标记 },用到的data
data() {
return { points: [], canvasTxt: null, startX: 0, startY: 0, moveY: 0, moveX: 0, endY: 0, endX: 0, w: null, h: null, isDown: false, color: "#000", linewidth: 3, isDraw: false //签名标记 }; },