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Add diff tool to

Henry Heino requested to merge screenshots-diff-tool into master

Adds a diff tool to the student and grader views for the HTML generated by

How Tolerance Works

Suppose p1 and p2 represent the actual and expected values of some pixel (respectively).

Then, defining Δr = p1.r - p2.r, Δg = p1.g - p2.g, Δb = p1.g - p2.g, Δa = p1.a - p2.a, if Δr² + Δg² + Δb² + Δa² ≥ tolerance, then the two pixels are considered different.

Adjusting Tolerance

Tolerance can be adjusted through the HTML page's URL. For example, if viewing file:///tmp/mozilla_selenite0/Screenshots-3-2.html, navigate to file:///tmp/mozilla_selenite0/Screenshots-3-2.html?tolerance=256 for a version with tolerance=256.


Fullscreen window: three columns for each test, logs number of different pixels Small window: Columns are thinner


Test locally

Test with Ed

Example Diffs (somewhat buggy solution)

Edited by Henry Heino

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