标签包括直线、矩形、多边形、圆等等，可以控制这些元素的样式和格式。
Specific tags are available to describe lines, rectangles, polygons, and circles, among others, and you have full control over the style and formatting of the different elements.
基本形状：矩形、圆、椭圆、直线、折线以及多边形。
Basic shapes: rectangles, circles, ellipses, lines, polylines, and polygons.
Canvas API是一个低级画图api，它支持创建直线、曲线、多边形和圆圈，并用彩色、渐变色等填充它们。
The Canvas API is a low level API for drawing. It lets you create lines, curves, polygons, and circles and fill them in with colors, gradients, and so on.
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