如何检查画布上是否绘制了某些东西 [英] How to check if something is drawn on canvas

问题描述

如何检查画布上是否有数据或绘制的东西?

How do I check if there is data or something drawn on a canvas?

我有这个 <canvas id="my-canvas"></canvas> 元素，我想检查我的画布上是否画了一些东西.

I have this <canvas id="my-canvas"></canvas> element, and I want to check if my canvas has something drawn on it.

推荐答案

与其检查每个像素，不如只在画布被填满或描边时进行记录，效率更高.

Instead of checking every single pixel, it may be much more efficient to merely record every time the canvas gets filled or stroked.

一旦填充、描边或已经发生，那么您就知道已经绘制了一些东西.

Once a fill or stroke or has happened, then you know that something has been drawn.

当然，如何"是特定于应用程序的，因为我们首先不知道您的画布是如何绘制的.

Of course 'how' is very application specific, since we don't know how your canvas is getting drawn on in the first place.

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