Question

I am developing a scribble type app in java swing. It is in a rudimentary stage and is shown here.

I have implemented the undo feature which undoes the last drawn stroke upto. The undo feature can be done upto a maximum defined undo levels.

The undo feature works by copying the contents of the drawing canvas after each stroke in an Image array.
This array acts like a First-In-Last-Out Stack. When undo is clicked the stack is poped
and the obtained image is drawn on screen.

Now the problem I am facing is, the current method of implementation of undo takes up too much memory. At undo levels of 20, almost 70-80 MB of memory is used up, and at levels of 30, heap overflow occurs.

Is there a better way of implementing the undo feature ? Thanks.

EDIT : I found some useful information here which may be helpful.

Answer 1

You need to represent the steps in your drawing differently. In the current approach you are using, you save the Canvas each time anew as an uncompressed picture – and that is memory-greedy.

Try to refactor your code so that only the strokes being drawn on the Canvas are saved into the stack. This will put a little bit more overhead when rendering the picture (you would need to redraw the entire canvas each time a change occurs), but Java is designed to deal with that.

Having saved only shapes, the memory requirements should decrease significantly. Use the Shape class to represent the strokes on the canvas.