Is it possible to have git gui / gitk look good on a retina Macbook Pro?

You can also use Retinizer which I guess will edit the Info.plist for you.

https://sites.google.com/a/mikelpr.com/retinizer/

open /System/Library/Frameworks/Tk.framework/Versions/Current/Resources/

Drag&drop Wish into Retinizer. Retinize. Voilà !

The solution pointed by @patrick-browne works like a charm and it is simpler, in fact, given that I already did the another approach pointed by @pius too.

As @joe said, just install retinizer with brew cask, then drag Wish and drop into Retinizer:

1. $ brew cask install retinizer

2. $ open /System/Library/Frameworks/Tk.framework/Versions/Current/Resources/

3. Drag Wish and drop into Retinizer

Update August 28, 2013: The pull request I submitted has been accepted, so I expect the problem will be fixed at the source, hopefully in release 1.9. If you can't wait, follow the work-around presented below.

1. Open your terminal and navigate to /System/Library/Frameworks/Tk.framework/Version/8.5/Resources/
2. Use an editor to open the Info.plist file inside the Wish.app folder (I used sudo emacs Wish.app/Contents/Info.plist)
3. Add the following two lines to the file, before </dict> and save it: <key>NSHighResolutionCapable</key>
<true/>
4. Make the OS reload the info file. This can be achieved with these commands:
   sudo cp -R Wish.app WishCopy.app
sudo mv Wish.app WishOriginal.app
sudo mv WishCopy.app Wish.app
5. Try running open Wish.app to see if it worked. If it did, it should work for gitk as well.
6. Do the same thing for git gui, but this time do it on the Git Gui.app (mine was in /usr/local/git/share/git-gui/lib/)

Oh, and I should probably mention that I found out about the NSHighResolutionCapable key from the tcl-mac mail-list, specifically from an e-mail by Kevin Walzer.

Here is a screenshot of the nice crisp fonts: