CODEWITHSUNDEEP
androiddrawingandroid-canvas
Manitoba
Manitoba

Reputation: 8702

Store drawing canvas and restore it later

I've made a simple whiteboard on my Android app, where the user can draw something. I want to add an Undo feature so that he will be able to go back to his previous action.

On my Touch Start event, I've added the following code which basically adds the current canvas to an ArrayList and create a new one to avoid same reference.

previousDrawing.add(this.canvas);
this.canvas = new Canvas(this.bitmap);

Then, in my undo method, I've added the following code:

if (previousDrawing.size() > 0)
{
     // Remove last
    this.canvas = previousDrawing.remove(previousDrawing.size() - 1);
    this.canvas.setBitmap(this.bitmap);
}

It doesn't work at all. I mean, I'm able to draw on my canvas using this.canvas.drawPath(this.path, this.paint); but not to save and restore a previous canvas.

Could you help me to do that ?

Thanks in advance.

EDIT : I've also tryied to use the saveLayer method. But when I save, I'm no longer able to draw on the canvas. Is this a normal behaviour ?

Upvotes: 1

Views: 2963

Answers (2)

NaviRamyle
NaviRamyle

Reputation: 4007

Try drawBitmap instead of setBitmap

this.canvas.drawBitmap(this.bitmap, 0, 0, null);

Edit

if (previousDrawing.size() > 0)
{
     // Remove last
    this.bitmap = previousDrawing.get(previousDrawing.size() - 1);
    this.canvas.drawBitmap(this.bitmap, 0, 0, null);
    previousDrawing.remove(previousDrawing.size() - 1);
}

Reference link

Upvotes: 3

Leonidos
Leonidos

Reputation: 10518

canvas doesnt hold pixels. Bitmap does. So it is useless to save and restore canvas. You can save and restore bitmap, but it is very memory consuming operation.

You better log user drawing actions. To go back in history you should redraw all actions from the beggining except the last one. To make it faster you can keep several key history bitmaps. Because redrawing all from the beggining is slow...

Upvotes: 0

Related Questions