使用单引号是因为如果需要绘制多个字，则绘图命令中需要使用双引号，而您不能在双引号中再用双引号。
The single quotes are used because the double quotes are needed within the drawing command if more than one word is to be drawn, and you cannot have double quotes within double quotes.
图像组件复制到可绘图表面之前，其位置已有记录，能够保证绘制顺序正确。
Before the image components are copied to the drawable surface, their locations are recorded to ensure that they are drawn in the correct order.
cairo是一个免费的矢量绘图软件库，它可以绘制多种输出格式。
Cairo is a free software vector drawing library that can draw to multiple output formats.
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