Styling feature with CanvasGradient or CanvasPattern——使用CanvasGradient或者CanvasPattern为要素设置样式

First this example creates a reusable CanvasPattern and a CanvasGradient. The countries are loaded from a GeoJSON file. A style function determines for each country whether to use a fill with the pregenerated CanvasGradient (rainbow colors) or a CanvasPattern (repeating stacked circles).
首先这个例子创建了一个可复用的CanvasPattern和CanvasGradient。国家数据从GeoJSON文件中加载。样式函数决定了每一个国家是否使用预先创建的CanvasGradient（多彩色）或者CanvasPattern（重复堆叠的圆）来填充。

代码：