如何在android中绘制位图? [英] How to draw on Bitmap in android?

问题描述

我正在尝试弄清楚如何在 android 中绘制位图，并为撤消功能保留这些更改后的位图的副本.

I'm trying to figure out how to draw on a bitmap in android, and keep a copy of these changed bitmaps for an undo function.

Bitmap b = ...
Paint p = new Paint();
canvas.drawBitmap(b, new Matrix(), null);
canvas.drawCircle(0,0,20,20);
//does Bitmap b have the circle drawn on it next time?

或者如何在使用画布绘制位图后获取位图(我想保留一堆位图，其中包含画布绘制应用的更改)?也许我完全错了.

Or how do I get the bitmap after its been drawn on with the canvas(I want to preserve a stack of bitmaps with the changes applied by canvas drawing)? Maybe I'm going about this entirely wrong.

推荐答案

使用 new Canvas(Bitmap bitmap) 为 Canvas 提供一个 Bitmap绘图操作的结果.

Use new Canvas(Bitmap bitmap) to provide a Canvas with a Bitmap which will contain the result of your drawing operations.

您使用 drawBitmap 在 Canvas 上绘制的原始 Bitmap 永远不会被修改.

The original Bitmap that you draw on your Canvas with drawBitmap will never be modified.

在用户完成每个操作后，您可能会:

After each operation done by the user you might:

• 在内存中保留已完成操作的列表
• 使用 Bitmap.compress 将中间结果保存到外部存储

另一种方法是使用 LayerDrawable 将连续的绘制操作堆叠在一起.您可以想象允许用户禁用每个单独的操作.

Another approach could be to use a LayerDrawable to stack successive drawing operations on top of each other. You can imagine allowing the user to disable each individual operation done.

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