Changes at the request of Dave Neary on the developer mailing list.  
I am changing many of the bugzilla reports that have not specified a target
milestone to Future milestone.  Hope that is acceptable.  

*** Bug 137113 has been marked as a duplicate of this bug. ***

History brush does not paint with plain colour, but with pixels taken
from the same position in some historic (or future) state of the
image. Otherwise it behaves like a normal brush. By default it paints
with pixels of the image  as it was opened (or newly created), but any
other state can be selected in a history palette (Undo history palette
of the Gimp). (The palette should have a checkboxes to select a
history level for history brush use and it shall keep future states --
when you revert for example 10 levels back, last 10 levels should be
for exapmple grey to make clear they are in future, but selectable for
history brush purposes).

This tool is very useful when retouching and can save a lot of time
and nerves. For example you apply a filter to the entire image, but
then you want to revert some small parts of the image. The history
brush is the quickest and easiest way to do it. Layers etc. can do the
same work, but harder and you have to plan it before , for example,
apllying the filter.

Created attachment 25664 [details]
painting with a future image state in photoshop 7

See also bug #170707.

Actually this shouldn't be hard to implement but perhaps it is a good idea to deal with bug #170707 before trying to implement an Undo brush.

Now that Edit->Fade is implemented, the basic framework needed to implement this feature is in place. What remains to be decided is whether this should become a new tool or if there should be some way to use this with all paint tools. Other aspects of the user interface would also still have to be decided. Perhaps someone wants to write up a proposal that we can then discuss on the mailing-list.

That's somewhat right, however the fade dialog is modal for a reason,
it's kindof heart surgery with the chest wide open, fiddling with two
states of the undo stack. A history brush would have to reverse-apply
all undo steps to a temp drawable in order to get a safe source to
clone from.

You can get a history brush with GIMPs buffers feature. To save and restore a current state (either past or future), do the following:
1. make the Buffers tab visible: click the small triangle in the upper right corner of a tab and select 'Buffers' from the popup menu.
2. save the current visible with Edit/Buffer/Copy named… and give it a name. It will appear in the Buffers tab then. 
2. work on your image or undo some steps
3. select the saved state in the Buffers tab, right click on it and select 'Paste buffer'. This will insert it as a new floating selection layer. Make a new layer of it. 
4. Create a layer mask on the new layer with the option 'Black (full transparency)'
5. Click on the layer mask and paint with a white brush or pencil - this will make the desired parts of the saved state visible. 
Unlike PS you also can use gray to achieve a fading effect. 

If this was helpful, this old bug can become closed IMO.

This bug cannot be closed unless there is simple one-click tool to make the same abilities, as Photoshop does.

I have placed bounty 30$ on bountysource for this bug. It expires in 6 month.
Hope it will be fixed.

https://www.bountysource.com/issues/1335023-wishing-for-history-brush

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