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：
- 组织数据；
- 画面绘制；
- 数据动画的实现；
- 位移坐标绘制
- 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
