1392465 - add paint flashing-like mode to reftest harness for another way to test invalidation

Status: NEW

(Testing :: Reftest, enhancement, P5)

Description

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

I was thinking it might be useful (and also probably pretty simple) to add a mode similar to paint flashing (see the nglayout.debug.paint_flashing preference) to the reftest harness.  This could be useful for testing some things related to invalidation.

In particular, if we had an API that were something like:
  SpecialPowers.colorNextPaint("rgb(0, 0, 255, 0.4)");
that would draw the given color on top of the areas repainted in the next repaint, then this could be compared with a reference in which the "repainted" area was overlaid by a div with that background color.

At the very least, this could be used to regression test bug 995410 (i.e., prevent that regression *in the reftest harness* from happening again -- a bug where we broken the reftest harness's partial invalidation mechanism and made it always fully repaint the snapshot).

I'm curious if others think this would be useful for other things.

Comment 1

[Kartikaya Gupta (email:[e-mail])]

Dropping stale needinfo. This sounds potentially useful, but I don't think any staff would actually work on it in the forseeable future. Marking P5; if volunteers want to submit a patch I'm happy to review.