基于canvas绘图 缩放 做标记
技术要点：
1.img 绘制到canvas
2.绘制完成以后进行拖拽，缩放
3.使用canvas画图，在绘制的img上进行标记划线，当然可以实现跟过功能，例如百度地图的功能，做单个标记，区域标记等。
4.实现坐标等转换，标记区域的所有坐标都是基于相对原始图片的坐标，便于其他操作。
实际项目中的开发实现效果截图如下：
点击边界标记，就可以开始左键划线功能，会自动形成闭合区域，点击右键结束划线。同时可以删除当前绘制的区域。
区域标记完成以后，就可以进行设备的选择，设备从左侧列表点击以后，放到右侧canvas 的区域，放下后还可以继续拖拽改变其位置，而且保持对应关系。
这些标记区域和标记点都可以基于底图的缩放和拖拽进行位置的等比例渲染，但是保存的坐标始终是基于原图的。
部分效果源码，本地看的话需要给img 图片路径，正确的路径。
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>标记</title>
</head>
<style>
html, body {
height: 100%;
min-height: 100%;
overflow: hidden;
}
* {
margin: 0;
padding: 0;
box-sizing: border-box;
border:none;
}
.canvasWrap {
width: 100%;
height: 100%;
background: #ccc;
}
.mark_list{
position: absolute;
top: 20px;
right: 10px;
}
.mark_list li{
float: left;
width: 100px;
border-radius: 4px;
border: 1px solid #ccc;
list-style: none;
line-height: 30px;
text-align: center;
color:#333;
background: #fff;
cursor: pointer;
}
.mark_list li:hover{
background: #009a8f;
color:#fff;
}
</style>
<body>
<div class="canvasWrap" id="wrap">
<canvas id="draw">
</canvas>
<ul class="mark_list">
<li class="border_mark">标记区域</li>
<li>标记点位</li>
</ul>
</div>
</body>
<script>
function MarkPoints(Imgurl) {
this.imgX = 0;//在画布上图片的X偏移量
this.imgY = 0;//在画布上图片的Y偏移量
this.imgScale = 1;//图片的缩放比例
this.rateNum;//图片高度自适应比例,图片等比居中展示在canvas
this.scaleFlag = 0;//缩放因子，最大缩放9,最小缩放-9
this.context;
this.img;
this.pos={};//每次拖拽前坐标保存
this.dragFlag=false;//是否可拖拽当前img，默认不能
this.markFlag=false;//标记区域开启关闭flag
this.CreatLinepoints = [];//每次创建新区域的坐标集合
this.allMarkLins = [];//已创建的区域集合，例如[[{x,y},{x,y},{x,y}],[{n,m},{n,m},{n,m}]]目前只需要一个区域，所以数组内部只有一项
this.getImgLoad(Imgurl);
this.init();
document.oncontextmenu = new Function("event.returnValue=false;");
document.onselectstart = new Function("event.returnValue=false;");
}
MarkPoints.prototype = {
getImgLoad: function (Imgurl) {
var _this = this;
var wrap = document.getElementById('wrap');
_this.canvas = document.getElementById('draw');
_this.context = draw.getContext('2d');
_this.canvas.height = wrap.offsetHeight;
_this.canvas.width = wrap.offsetWidth;
_this.img = new Image();
_this.img.onload = function () {
_this.imgX = 0;
_this.imgY = 0;
_this.imgScale = 1;
_this.imgScale=_this.rateNum = _this.canvas.height / _this.img.naturalHeight;
_this.imgX = (_this.canvas.width - _this.img.naturalWidth * _this.imgScale * _this.rateNum) / 2;//默认进来当前图像剧中显示
/*画出当前图片*/
_this.drawImg();
}
_this.img.src = imgUrl;
},
getNewPoints: function (points) {
var _this=this;
var newPointAry = [];
for (var i = 0; i < points.length; i++) {
var obj = {};
obj.x = points[i].x * _this.imgScale + _this.imgX;
obj.y = points[i].y * _this.imgScale + _this.imgY;
if (points[i].hasOwnProperty('mac')) {
obj.mac = points[i].mac;
obj.name = points[i].name || '';
}
newPointAry.push(obj);
}
return newPointAry;
},
drawImg: function () {
var _this = this;
_this.context.clearRect(0, 0, _this.canvas.width, _this.canvas.height);
_this.context.drawImage(_this.img, 0, 0, _this.img.naturalWidth, _this.img.naturalHeight, _this.imgX, _this.imgY, _this.img.naturalWidth * _this.imgScale * _this.rateNum, _this.img.naturalHeight * _this.imgScale * _this.rateNum);
if ( _this.allMarkLins.length) {
for (var m = 0; m < _this.allMarkLins.length; m++) {
var points = _this.allMarkLins[m];
var newPoints = _this.getNewPoints(points);
for (var i = 0; i < newPoints.length; i++) {
var can = _this.context;
can.beginPath();
can.arc(newPoints[i].x, newPoints[i].y, 6, 0, Math.PI * 2, true);
can.fillStyle = "#FF423E";
can.fill();
can.strokeStyle = "#FFF";
can.stroke();//画空心圆
can.closePath();
if (points.length >= 2 && i >= 1) {
can.strokeStyle = "#FF423E";
can.lineWidth = 2;
can.beginPath();
can.moveTo(newPoints[i - 1].x, newPoints[i - 1].y);
can.lineTo(newPoints[i].x, newPoints[i].y);
can.fillStyle = "#ff0000";
can.fill();
can.stroke();
can.closePath();
}
}
if (points.length >= 3) {
can.strokeStyle = "#FF423E";
can.lineWidth = 2;
can.beginPath();
can.moveTo(newPoints[newPoints.length - 1].x, newPoints[newPoints.length - 1].y);
can.lineTo(newPoints[0].x, newPoints[0].y);
can.stroke();
can.closePath();
}
}
;
}
},
init:function () {
var _this=this;
_this.canvas.onmousedown=function(event){
_this.clickDown(event);
};
_this.canvas.onmousemove=function(event){
_this.mouseMove(event)
};
_this.canvas.onmouseup=function (event) {
_this.mouseUp(event);
}
_this.canvas.onmousewheel=function (event) {
_this.onmouseWheel(event);
}
document.getElementsByClassName('border_mark')[0].onclick=function () {
_this.MarkBorderline();
}
},
/*计算当前鼠标位置距离canvas的偏移量*/
xyToCanvas:function(ele,x,y){
var _this=this;
var obj = _this.canvas.getBoundingClientRect();
return {
x: x - obj.left,
y: y - obj.top
};
},
/*鼠标单击事件*/
clickDown:function(event){
var _this=this;
if (_this.markFlag) {
_this.canvas.style.cursor = "none";
if (event.button == 2) {
_this.markFlag = false;
_this.dragFlag = true;
_this.canvas.style.cursor = "normal";
_this.drawImg();
return;
} else {
var posXY = _this.xyToCanvas(_this.canvas, event.clientX, event.clientY);
posXY.x = (posXY.x - _this.imgX) / _this.imgScale;
posXY.y = (posXY.y - _this.imgY) / _this.imgScale;
_this.CreatLinepoints.push(posXY);
_this.allMarkLins.pop();
_this.allMarkLins.push(_this.CreatLinepoints);
_this.drawImg();
}
return;
}
if ( event.button == 0) {//点击鼠标左键
_this.dragFlag = true;
_this.canvas.style.cursor = "move";
_this.pos = _this.xyToCanvas(_this.canvas, event.clientX, event.clientY);
}
},
/*鼠标移动事件*/
mouseMove:function(event){
var _this=this;
/*拖拽*/
if (_this.dragFlag) {
_this.canvas.style.cursor = "move";
var pos1 = _this.xyToCanvas( _this.canvas, event.clientX, event.clientY);
var x = pos1.x - _this.pos.x;
var y = pos1.y - _this.pos.y;
_this.pos = pos1;
_this.imgX += x;
_this.imgY += y;
_this.drawImg();
}
/*边界标记*/
if (!_this.dragFlag&& _this.markFlag) {
var pos1 = _this.xyToCanvas(_this.canvas, event.clientX, event.clientY);
var can = _this.context;
can.clearRect(0, 0, _this.canvas.width, _this.canvas.height);
_this.drawImg();
/*画跟随圆点*/
can.beginPath();
// can.fillText('[' + point.x + ', ' + point.y + ']', 15, 25 * (points.length + 1))
can.arc(pos1.x, pos1.y, 6, 0, Math.PI * 2, true);
can.fillStyle = "#FF423E";
can.fill();
can.strokeStyle = "#FFF";
can.stroke();//画空心圆
can.closePath();
/*当前的坐标未结束那么继续 跟随直线*/
if (!_this.CreatLinepoints.length) return;
can.strokeStyle = "red";
can.beginPath();
can.moveTo(_this.CreatLinepoints[_this.CreatLinepoints.length - 1].x * _this.imgScale + _this.imgX, _this.CreatLinepoints[_this.CreatLinepoints.length - 1].y * _this.imgScale + _this.imgY);
can.lineTo(pos1.x, pos1.y);
can.stroke();
can.closePath();
}
},
/*鼠标放开事件*/
mouseUp:function (event) {
var _this=this;
_this.dragFlag=false;
if (_this.markFlag) {
_this.canvas.style.cursor = "none";
return;
}
_this.canvas.style.cursor='default';
},
/*鼠标滚轮事件*/
onmouseWheel:function(event){
var _this=this;
var pos =_this.xyToCanvas(_this.canvas, event.clientX, event.clientY);
event.wheelDelta = event.wheelDelta ? event.wheelDelta : (event.deltaY * (-40));
if (event.wheelDelta > 0 && _this.scaleFlag < 9) {
_this.imgScale *= 2;
_this.imgX = _this.imgX * 2 - pos.x;
_this.imgY = _this.imgY * 2 - pos.y;
_this.scaleFlag += 1;
}
if (event.wheelDelta < 0 && _this.scaleFlag > -9) {//缩小
_this.imgScale *= 0.5;
_this.imgX = _this.imgX * 0.5 + pos.x * 0.5;
_this.imgY = _this.imgY * 0.5 + pos.y * 0.5;
_this.scaleFlag -= 1;
}
_this.drawImg();
},
/*边界标记*/
MarkBorderline: function () {
var _this=this;
_this.markFlag = true;//切换为true，禁止拖拽，只能标记
_this.canvas.style.cursor = "none";
_this.CreatLinepoints = [];
_this.allMarkLins.push([]);
},
/*删除标记区域*/
deleteArea: function (id) {
var _this = this;
_this.allMarkLins.splice(id, 1);
_this.drawImg();
},
}
var imgUrl = 'img/girl.jpg';//图片路径
new MarkPoints(imgUrl);
</script>
</html>
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