LayerWindow: add ability to undo/redo layer 'meta-data' changes

[dsizzle]

• supports undo/redo of visibility, blend mode, transparency, and layer name.

Partially addresses #240

The remaining piece from the ticket is layer re-arranging. However, another area that should be improved is deleting a layer. Currently all layer settings are lost when you delete and then undo.

[dsizzle]

actually I got layer data working for undo, but not redo. that is to say:

• delete a layer
• undo delete layer -> layer name, blend mode etc. is restored
• redo delete layer
• undo delete layer -> layer data gone

but it's better than before. also works for merging/undo merge the same way.

[humdingerb]

Nice! I gave it a little test run. Here's one thing I found:

• Open ducky and Walter_the_OS
• Copy Walter as a new layer on top of ducky
• Change Walter's layer to "Color burn"
• Change Walter layer's alpha to 30%
• Delete Walter layer
• Undo "Delete layer" -->The alpha is back at 100%. And the alpha slider has no effect, until you click the Walter (or any other layer, and back to the Walter layer) in the Layers window.

[dsizzle]

I figured out the problem, not sure of the fix yet. A difference with this change is that when you un-delete a layer, it gets selected. Previously undoing a layer deletion kept the current selection (which I think is wrong). Seems like some percentage of the time, the layer isn't really selected until you click on it, so the UI doesn't work. Hmm....

[dsizzle]

ok. I think it's fixed by sort of forcing an update of the Layer window.

[humdingerb]

Hmm... doing the same as described above, still the transparency isn't restored after undoing the "Delete layer".

[dsizzle]

doing the same as described above, still the transparency isn't restored after undoing the "Delete layer".

but does everything else work?

[humdingerb]

Not completely. If I do this:

• duplicate layer
• change mode
• change alpha
• delete layer

then undo one by one:

• layer gets undeleted --> however: alpha = 100%
• After that, undo works as expected

then re-do everything. then undo one by one again:

• layer gets undeleted --> however: mode= normal, alpha 100%
• next undo says: "Undo transparency" --> however: not alpha gets changed, but mode
• After that, undo works as expected

It's a bit complicated... best try yourself, do these steps from above:

• duplicate layer
• change mode
• change alpha
• delete layer then undo and redo and undo again. first undo wors (aside from transparency), second undo is different than the first one. Complicated.

[dsizzle]

So the transparency part is a problem. But I mentioned above that undo/redo/undo/redo doesn’t work. But undo/redo should.

[dsizzle]

Ok, I fixed the transparency for undoing a deleted layer. But still, undo/redo/undo/redo doesn't work, as before.

I had forgotten I needed to do a bit of a hack for transparency because it's a live updating slider. So I only want an Undo event when you stop sliding, but I need to update the layer transparency every time the slider moves. That means I need to keep track of what the original transparency was before the user started messing with it. I think it's good now.

[humdingerb]

Sorry, I misunderstood and thought you've fixed it completely. :) Anyway, aside from redoing a deleted layer, it works very nicely now. Merge!