Undo / Redo with 2 Canvases in Fabric.JS
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Undo / Redo Question

I have a small JSFiddle that allows me to undo and redo. I have a second fiddle that has 2 canvases (for a front and back) and I’ve been trying to incorporate the functionality from the first JSFiddle into it. Basically, in the second JSFiddle, I need to be able to toggle between the Front and Back and be able to Undo / Redo.

Here is the original Undo / Redo JSFiddle: https://jsfiddle.net/code4ever/zkqw7980/

And here is what I’ve been trying to incorporate it into: https://jsfiddle.net/code4ever/ejrcyq9s/

Please let me know if I can add more information to help you provide a solution. Thanks!

Using a stack of n canvases (in this case 2) is not a very efficient way to store previous states. You should serialize the fabric.js canvas as JSON each time you make a change and store a list of past states that way. Then you don't need to keep an extra canvas in the DOM.
slang800 28 days ago
I would go a step even further, and store only the differences (deltas) between each JSON history state using a library like this: http://json-delta.readthedocs.io/en/latest/javascript.html or https://github.com/benjamine/jsondiffpatch.
kostasx 28 days ago
Here's something I've quickly set up to test the JSON diff strategy: https://codepen.io/kostasx/pen/YjGrYB?editors=0011 Works only with text modification at the current moment.
kostasx 28 days ago
@slang800, thank you for that suggestion! @kostasx, and thank you for yours. I'm checking those out now, they look interesting!
sharper 28 days ago
awarded to Wuddrum

Crowdsource coding tasks.

1 Solution

Here's my solution: JSFiddle

It's based on the example you provided, but with some bugs fixed.

Undo/Redo supports all elements (BG/Text/Frame/Accents) and both (back and front) canvas. Canvas have their own separate undo states of course.

EDIT: Fixed a bug JSFiddle

This looks great. Mind if I pop back for follow up questions (for tips of course?). Thanks Wuddrum
sharper 22 days ago
I did notice one thing: When I add a background, and then an accent image, but then undo all changes and then select a frame, the old background reappears. Do you find that it does this for you too?
sharper 22 days ago
Didn't catch that one when I was testing, but yes, it's happening for me also. I'm looking into it.
And as always, I'll answer follow up questions.
Wuddrum 22 days ago
I've updated my solution with a fixed version. Everything seems to be working now.
Wuddrum 22 days ago
Hey, it's working for me too. Thank you!
sharper 22 days ago
Thank you for the tip!
Wuddrum 21 days ago
You are most welcome
sharper 21 days ago