Undo Redo

[matanox]

It is inconceivable that user initiated modifications to the view cannot be undone; having the user manually undo them by whatever interaction tools they have to reverse the effects is not very reasonable approaching the year 2016. It's sort of a User eXperience dead end. This change should be done along with improving the separation between model and render layers.

Basic design can be:

• every action changing the view will be wrapped with a new function doWithUndo, which will push the current display state into an undo-redo buffer, before executing the action. E.g. doWithUndo(addNodeGroup(params)).
• an Undo function (here, it might benefit from d3's data driven animations, which can make the undo look gradual inline with the rest of the "feel").
• a redo function which moves the undo-redo pointer across the undo-redo array
• Some these functions will have to appropriately invalidate redos/undos once performed, to provide the consistent experience of undo/redo that we have in most applications that support undo-redo.

Those would be the high-level api. The lower level api serving them may be something like:

• historyBuffer
• getMaxSize - maximum size allowed for the buffer being somehow determined automatically relative to the amount of memory available or something like that.
• getCurrentBufferSize - using the function sizeof or otherwise.
• trimBuffer for pushing in a new snapshot while freeing up space by removing the oldest undo or something like that

So we have a buffer and a pointer.

What can be undone and redone?

• nodes on display
• node locations too! if window size changed, they should be ignored though (or adjusted in a simple way that is cognition-friendly)

What preserves during undo?

• selection status, (whether a node is selected or not); as much as the nodes are still on display after the undo; Give this a little more thought.

[matanox]

Might make sense using the ES6 objects coding style for this and whatever this touches; we don't need to support legacy browsers and stuff anyway... enough if it works with Chrome and FF, being an app/website for technical people..