This JPEG shows a screen-shot of TLIB's Visual Compare.  It
consists of two panels, with scroll bars and a button labeled
"Options."  The old version of a source file is shown in the left
panel, and the new version is shown in the right panel.  Lines
that differ are highlighted, and the parts of the lines that are
different are colorized, red for deleted text, green for inserted
text.  Line numbers are shown to the left of each panel, and
large unmodified blocks of text are omitted, for brevity.
The amount of "unmodified" context shown before and after each
block of changed text is adjustable via the Options button.