856499 - test_bug847890_paintFlashing.html does not actually detect painting due to changes

Status: NEW

(Core :: Layout, defect)

Description

[Ben Kelly [:bkelly, not reviewing]]

Attachment: Bogus test case that shows paint flashing always occurs with snapshotWindow()

Currently test_bug847890_paintFlashing.html uses the following logic:

  1) Call snapshotWindow() to capture "before" view state
  2) Set paintFlashing = true
  3) Modify the page content
  4) Call snapshotWindow() to capture "after" view state
  5) Compare snapshots to verify that paint flashing occurred.

Unfortunately, this does not actually test if paint flashing occurred due to changes to the page.

The snapshotWindow() function works by painting the current content into it a new Canvas element.  This means that paint flashing will always be triggered.

The end effect of this is really just that the test provides a misleading sense of what is being validated.  It may be worth restructuring it without content changes and a comment that describes how snapshotWindow() triggers a paint.