背景
前段时间工作室接到一个与地图相关的项目，我作为项目组成员主要负责地图方面的设计和开发。由于地图部分主要涉及的是前端页面的显示，作为一名Java后端的小白，第一次写了这么多HTML和JavaScript。
项目大概是需要将一张CAD的图(导出大概三十万条数据)叠加在地图上，在接Canvas之前考虑了很多种方案，最后都否定了。首先我们想利用百度地图原生的JavaScript API实现线和点的加载，但是经过测试，当数据达到2000左右，加载时间就已经达到了数十秒，后来直接测试了一万条数据，浏览器直接卡死了，这种方案很快就被否定了。然后我们又准备采用分割静态图的方法，将整个CAD图分割成地图瓦片，作为覆盖图层叠加在原来地图之上，在这一步中，由于CAD图的信息涉及到整个城市，信息量非常巨大，几乎没有找到合适软件能够导出一张这么大的图。后来仔细研究需求文档后又发现需要针对图的信息做操作，然后这种方案将近完成的时候被否定了。最后，偶然在Github上看到：https://github.com/lcosmos/map-canvas 这个实现台风轨迹，这个数据量非常庞大，当时打开时，看到这么多数据加载很快，感到有点震惊，然后自己研究了一番，发现作者采用的是Canvas作为百度的自定义覆盖层，说干就干，自己尝试写出了第一个版本，写上Ajax请求，效果十分震撼，将近秒级加载，加了计时器测试了一番性能，发现绘画只花了1ms左右，主要延时都在请求延时(90M左右的数据)，内存占用也非常少，这下放心多了，项目基本也可以完成了，然后当然是捣鼓传输延时，GZip等都用上了，最后也有了极大优化，客户看后觉得还十分不错。
系列文章：
效果图
(由于项目涉及国家机密，部分细节和图片不便于展示，但已经可以完成标题需求)
具体实现
(由于项目涉及国家机密，部分细节和图片不便于展示，但已经可以完成标题需求)
HTML测试页：
<!DOCTYPE html>
<html>
<head>
<title>百度地图Canvas海量折线</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0, user-scalable=no">
<link rel="stylesheet" href="css/style.css">
<script type="text/javascript" src="https://api.map.baidu.com/api?v=2.0&ak=nuWah68S1WieW2AEwiT8T3Ro&s=1"></script>
<script type="text/javascript" src="js/jquery.min.js"></script>
</head>
<body>
<div id="map"></div>
<script type="text/javascript" src="pointLine.js"></script>
<script type="text/javascript">
var map = new BMap.Map('map', {
minZoom: 5
});
map.centerAndZoom(new BMap.Point(112.954699, 27.851256), 13);
map.enableScrollWheelZoom(true);
map.setMapStyle({
styleJson: styleJson
});
$.getJSON('line.json', function (result) {
var pointLine = new PointLine(map, {
//线条宽度
lineWidth: 2,
//线条颜色
lineStyle: '#F9815C',
//数据源
data: result,
//事件
methods: {
click: function (e, name) {
console.log('你当前点击的是' + name);
},
// mousemove: function (e, name) {
// console.log('你当前点击的是' + name);
// }
}
});
})
</script>
</body>
</html>
核心JavaScript：pointLine.js
(function (global, factory) {
typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
typeof define === 'function' && define.amd ? define(factory) :
(global.PointLine = factory());
}(this, (function () { 'use strict';
function CanvasLayer(options) {
this.options = options || {};
this.paneName = this.options.paneName || 'labelPane';
this.zIndex = this.options.zIndex || 0;
this._map = options.map;
this._lastDrawTime = null;
this.show();
}
CanvasLayer.prototype = new BMap.Overlay();
CanvasLayer.prototype.initialize = function (map) {
this._map = map;
var canvas = this.canvas = document.createElement('canvas');
var ctx = this.ctx = this.canvas.getContext('2d');
canvas.style.cssText = 'position:absolute;' + 'left:0;' + 'top:0;' + 'z-index:' + this.zIndex + ';';
this.adjustSize();
this.adjustRatio(ctx);
map.getPanes()[this.paneName].appendChild(canvas);
var that = this;
map.addEventListener('resize', function () {
that.adjustSize();
that._draw();
});
return this.canvas;
};
CanvasLayer.prototype.adjustSize = function () {
var size = this._map.getSize();
var canvas = this.canvas;
canvas.width = size.width;
canvas.height = size.height;
canvas.style.width = canvas.width + 'px';
canvas.style.height = canvas.height + 'px';
};
CanvasLayer.prototype.adjustRatio = function (ctx) {
var backingStore = ctx.backingStorePixelRatio || ctx.webkitBackingStorePixelRatio || ctx.mozBackingStorePixelRatio || ctx.msBackingStorePixelRatio || ctx.oBackingStorePixelRatio || ctx.backingStorePixelRatio || 1;
var pixelRatio = (window.devicePixelRatio || 1) / backingStore;
var canvasWidth = ctx.canvas.width;
var canvasHeight = ctx.canvas.height;
ctx.canvas.width = canvasWidth * pixelRatio;
ctx.canvas.height = canvasHeight * pixelRatio;
ctx.canvas.style.width = canvasWidth + 'px';
ctx.canvas.style.height = canvasHeight + 'px';
// console.log(ctx.canvas.height, canvasHeight);
ctx.scale(pixelRatio, pixelRatio);
};
CanvasLayer.prototype.draw = function () {
var self = this;
var args = arguments;
clearTimeout(self.timeoutID);
self.timeoutID = setTimeout(function () {
self._draw();
}, 15);
};
CanvasLayer.prototype._draw = function () {
var map = this._map;
var size = map.getSize();
var center = map.getCenter();
if (center) {
var pixel = map.pointToOverlayPixel(center);
this.canvas.style.left = pixel.x - size.width / 2 + 'px';
this.canvas.style.top = pixel.y - size.height / 2 + 'px';
this.dispatchEvent('draw');
this.options.update && this.options.update.call(this);
}
};
CanvasLayer.prototype.getContainer = function () {
return this.canvas;
};
CanvasLayer.prototype.show = function () {
if (!this.canvas) {
this._map.addOverlay(this);
}
this.canvas.style.display = 'block';
};
CanvasLayer.prototype.hide = function () {
this.canvas.style.display = 'none';
//this._map.removeOverlay(this);
};
CanvasLayer.prototype.setZIndex = function (zIndex) {
this.canvas.style.zIndex = zIndex;
};
CanvasLayer.prototype.getZIndex = function () {
return this.zIndex;
};
var tool = {
merge: function merge(settings, defaults) {
Object.keys(settings).forEach(function (key) {
defaults[key] = settings[key];
});
},
//计算两点间距离
getDistance: function getDistance(p1, p2) {
return Math.sqrt((p1[0] - p2[0]) * (p1[0] - p2[0]) + (p1[1] - p2[1]) * (p1[1] - p2[1]));
},
//判断点是否在线段上
containStroke: function containStroke(x0, y0, x1, y1, lineWidth, x, y) {
if (lineWidth === 0) {
return false;
}
var _l = lineWidth;
var _a = 0;
var _b = x0;
// Quick reject
if (y > y0 + _l && y > y1 + _l || y < y0 - _l && y < y1 - _l || x > x0 + _l && x > x1 + _l || x < x0 - _l && x < x1 - _l) {
return false;
}
if (x0 !== x1) {
_a = (y0 - y1) / (x0 - x1);
_b = (x0 * y1 - x1 * y0) / (x0 - x1);
} else {
return Math.abs(x - x0) <= _l / 2;
}
var tmp = _a * x - y + _b;
var _s = tmp * tmp / (_a * _a + 1);
return _s <= _l / 2 * _l / 2;
}
};
var PointLine = function PointLine(map, userOptions) {
var self = this;
self.map = map;
self.lines = [];
self.pixelList = [];
//默认参数
var options = {
//线条宽度
lineWidth: 1,
//线条颜色
lineStyle: '#F9815C'
};
//全局变量
var baseLayer = null,
width = map.getSize().width,
height = map.getSize().height;
function Line(opts) {
this.name = opts.name;
this.path = opts.path;
}
Line.prototype.getPointList = function () {
var points = [],
path = this.path;
if (path && path.length > 0) {
path.forEach(function (p) {
points.push({
name: p.name,
pixel: map.pointToPixel(p.location)
});
});
}
return points;
};
Line.prototype.draw = function (context) {
var pointList = this.pixelList || this.getPointList();
context.save();
context.beginPath();
context.lineWidth = options.lineWidth;
context.strokeStyle = options.lineStyle;
context.moveTo(pointList[0].pixel.x, pointList[0].pixel.y);
for (var i = 0, len = pointList.length; i < len; i++) {
context.lineTo(pointList[i].pixel.x, pointList[i].pixel.y);
}
context.stroke();
context.closePath();
context.restore();
};
//底层canvas渲染，标注，线条
var brush = function brush() {
var baseCtx = baseLayer.canvas.getContext('2d');
if (!baseCtx) {
return;
}
addLine();
baseCtx.clearRect(0, 0, width, height);
self.pixelList = [];
self.lines.forEach(function (line) {
self.pixelList.push({
name: line.name,
data: line.getPointList()
});
line.draw(baseCtx);
});
};
var addLine = function addLine() {
if (self.lines && self.lines.length > 0) return;
var dataset = options.data;
dataset.forEach(function (l, i) {
var line = new Line({
name: l.name,
path: []
});
l.data.forEach(function (p, j) {
line.path.push({
name: p.name,
location: new BMap.Point(p.Longitude, p.Latitude)
});
});
self.lines.push(line);
});
};
self.init(userOptions, options);
baseLayer = new CanvasLayer({
map: map,
update: brush
});
this.clickEvent = this.clickEvent.bind(this);
this.bindEvent();
};
PointLine.prototype.init = function (settings, defaults) {
//合并参数
tool.merge(settings, defaults);
this.options = defaults;
};
PointLine.prototype.bindEvent = function (e) {
var map = this.map;
if (this.options.methods) {
if (this.options.methods.click) {
map.setDefaultCursor("default");
map.addEventListener('click', this.clickEvent);
}
if (this.options.methods.mousemove) {
map.setDefaultCursor("default");
map.addEventListener('mousemove', this.clickEvent);
}
}
};
PointLine.prototype.clickEvent = function (e) {
var self = this,
lines = self.pixelList;
if (lines.length > 0) {
lines.forEach(function (line, i) {
for (var j = 0; j < line.data.length; j++) {
var beginPt = line.data[j].pixel;
if (line.data[j + 1] == undefined) {
return;
}
var endPt = line.data[j + 1].pixel;
var curPt = e.pixel;
var isOnLine = tool.containStroke(beginPt.x, beginPt.y, endPt.x, endPt.y, self.options.lineWidth, curPt.x, curPt.y);
if (isOnLine) {
self.options.methods.click(e, line.name);
return;
}
}
});
}
};
return PointLine;
})));
测试数据：line.json
扫一扫
被折叠的 条评论
为什么被折叠?
到【灌水乐园】发言
