This directory contains the source of screenshots diff viewer used on Perfetto CI. The way it works as follows:
When a screenshot test is failing, the testing code will write a line of the form
failed-screenshot.png;failed-screenshot-diff.png
To a file called report.txt. Diff viewer is just a static page that uses Fetch API to download this file, parse it, and display images in a list of rows.
The page assumes report.txt to be present in the same directory, same goes for screenshot files. To simplify deployment, the viewer is developed without a framework and constructs DOM using document.createElement API.