From DesigningPatterns

Background

xxdiff is a graphical diff and merge tool. It comes with very comprehensive subversion support, although currently is has no built-in git support.

Installation

• Download and install xxdiff; I found RPMs for it here.
• Download and unpack the official xxdiff distribution in order to get the xxdiff Python scripts (including wrappers that make xxdiff play nicely with subversion).
• Install the Python scripts with python setup.py install.
• Modify the site-wide subversion config file (/etc/subversion/config) to use xxdiff and emacs (for creating comments, etc). Enter:

[helpers]
diff-cmd = xx-diff-proxy
diff3-cmd = xx-diff-proxy

• Create a wrapper around the xx-diff-proxy script that git can call for diffs. Here is /usr/bin/xx-git-diff:

#!/usr/bin/env sh
xx-diff-proxy $2 $5

• Modify the site-wide git config file. Enter:

git config --system diff.external xx-git-diff
git config --system merge.tool xxdiff

This should produce an /etc/gitconfig with:

[diff]
        external = xx-git-diff
[merge]
        tool = xxdiff

• /usr/designingpatterns/etc/profile sets the XXDIFFRC environment variable to /usr/designingpatterns/etc/xxdiffrc, which contains site-wide xxdiff customization (such as default font).
• Make this small change to the diffproxy.py script in /usr/lib/python2.4/site-packages/xxdiff/scripts.
  

The code before:

    if opts.merge:
        dargs.append('--merge')

The code after:

    if opts.merge:
        dargs.append('--merge')
        dargs.append('--show-merged-pane')

This will make the xxdiff adapter that subversion calls add a merge pane when (and only when) doing merges; there does not seem to be a way to configure xxdiff to do this on its own.