canvas图表(4) - 散点图

原文地址：canvas图表(4) - 散点图

今天开始完成散点图，做完这一节，我的canvas图表系列就算是完成了，毕竟平时最频繁用到的就是这几类图表了：柱状，折线，饼图，散点。经过编写canvas图表项目的实践，我对canvas也做到了比较深入的理解，也是越来越喜欢计算机图形相关的知识了。接下来canvas的学习会告一段落，我会继续接着学习webGL，同时学习使用blender建立简单的3D模型。

本节效果请看：散点气泡图https://edwardzhong.github.io/sites/demo/dist/chartpoint.html

经过学习之前的其他图表后，就会发现很多地方都是相似的，只是具体的细节有些区别，所以这次主要就是讲解散点图不同的部分，功能点包括：

1. 组织数据；
2. 画面绘制；
3. 数据动画的实现；
4. 位移坐标绘制
5. 鼠标事件的处理。

使用方式

用法基本跟柱状图和折线图类似，数据使用的是Echart的样例上的，但是它的数据格式太反人道了，我重新组织了数据格式，这样更符合我们的使用习惯。

	var con=document.getElementById('container');
	var point =new Point(con);
	point.init({
		title:'1990 与 2015 年各国家人均寿命与 GDP',
	 	xAxis:{
	 		name:'GDP',
	 		data:[10000,20000,30000,40000,50000,60000,70000],
	 		formatter:'$ {value}'
	 	},
	 	yAxis:{
			name:'AGE'
		},
		desc:{
			xVal:'gdp',
			yVal:'age',
			num:'number'
		},
		series:[{
			name:'1990',
			data:[
				{xVal:28604,yVal:77,num:17096869,name:'Australia'},
				{xVal:31163,yVal:77.4,num:27662440,name:'Canada'},
				{xVal:1516,yVal:68,num:1154605773,name:'China'},
				{xVal:13670,yVal:74.7,num:10582082,name:'Cuba'},
				{xVal:28599,yVal:75,num:4986705,name:'Finland'},
				{xVal:29476,yVal:77.1,num:56943299,name:'France'},
				{xVal:31476,yVal:75.4,num:78958237,name:'Germany'},
				{xVal:28666,yVal:78.1,num:254830,name:'Iceland'},
				{xVal:1777,yVal:57.7,num:870601776,name:'India'},
				{xVal:29550,yVal:79.1,num:122249285,name:'Japan'},
				{xVal:2076,yVal:67.9,num:20194354,name:'North Korea'},
				{xVal:12087,yVal:72,num:42972254,name:'South Korea'},
				{xVal:24021,yVal:75.4,num:3397534,name:'New Zealand'},
				{xVal:43296,yVal:76.8,num:4240375,name:'Norway'},
				{xVal:10088,yVal:70.8,num:38195258,name:'Poland'},
				{xVal:19349,yVal:69.6,num:147568552,name:'Russia'},
				{xVal:10670,yVal:67.3,num:53994605,name:'Turkey'},
				{xVal:26424,yVal:75.7,num:57110117,name:'United Kingdom'},
				{xVal:37062,yVal:75.4,num:252847810,name:'United States'}]
			},
			{
			name:'2015',
			data:[
				{xVal:44056,yVal:81.8,num:23968973,name:'Australia'},
			    {xVal:43294,yVal:81.7,num:35939927,name:'Canada'},
			    {xVal:13334,yVal:76.9,num:1376048943,name:'China'},
			    {xVal:21291,yVal:78.5,num:11389562,name:'Cuba'},
			    {xVal:38923,yVal:80.8,num:5503457,name:'Finland'},
			    {xVal:37599,yVal:81.9,num:64395345,name:'France'},
			    {xVal:44053,yVal:81.1,num:80688545,name:'Germany'},
			    {xVal:42182,yVal:82.8,num:329425,name:'Iceland'},
			    {xVal:5903,yVal:66.8,num:1311050527,name:'India'},
			    {xVal:36162,yVal:83.5,num:126573481,name:'Japan'},
			    {xVal:1390,yVal:71.4,num:25155317,name:'North Korea'},
			    {xVal:34644,yVal:80.7,num:50293439,name:'South Korea'},
			    {xVal:34186,yVal:80.6,num:4528526,name:'New Zealand'},
			    {xVal:64304,yVal:81.6,num:5210967,name:'Norway'},
			    {xVal:24787,yVal:77.3,num:38611794,name:'Poland'},
			    {xVal:23038,yVal:73.13,num:143456918,name:'Russia'},
			    {xVal:19360,yVal:76.5,num:78665830,name:'Turkey'},
			    {xVal:38225,yVal:81.4,num:64715810,name:'United Kingdom'},
			    {xVal:53354,yVal:79.1,num:321773631,name:'United States'}]
		}]
	});

数据动画

清除屏幕，然后重绘，实现动画效果。实现了气泡半径的缩放和气泡的位移动画，为了更加的美观，气泡使用了径向渐变createRadialGradient和阴影shadow，之前已经介绍过，不再详述。要注意的是，要谨慎使用阴影特性，因为它挺消耗性能，数据量一大，会卡的不要不要的