Gérard's been running into a number of issues affecting the creation of reftests due to the fact that Firefox does subpixel-precision layout and the font APIs on Linux only return pixel-precision data. The workaround for this seems to be to use fonts at sizes where it is known their metrics land on whole-pixel sizes. Many of our self-describing tests suffer from this problem. Their pass/ fail results can be determined accurately, but creating a pixel-perfect reference is difficult or impossible without altering the original test. Similar issues probably exist anywhere there is inconsistent pixel-rounding. For example, Firefox rounds border widths with different rules than it rounds box heights, making a reftest comparison between a solid border and a solid-color fixed-height block meaningless if their sizes involve fractional pixels. Which brings us to a suggestion from Jet: to require tests, insofar as possible, to align their layout to the px grid, so that they can be reliably associated to a reference. Is this something we want to do? It will drastically reduce our test coverage of pixel rounding. If not, what is the alternative? ~fantasaiReceived on Saturday, 17 March 2012 00:43:20 UTC
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