453103 - Reftest fail with subpixel rendering

Status: RESOLVED FIXED

(Core :: Layout, defect)

Description

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: fix

Like bug 452747, there are a few more reftests that fail on my Mac due to glyphs being rendered a little outside the (pixel-snapped) font-box and being clipped in the testcase and not the reference, or vice versa. These are all fixable by adding a little padding, or in one case it seems safer to just make the text be invisible via rgba(0,0,0,0).

Comment 1

[Jesse Ruderman]

Why are these reftest failures considered bugs in the tests rather than a bug in Gecko?  Why does adding padding fix them?

Comment 2

[Robert O'Callahan (:roc) (email my personal email if necessary)]

These tests assume that text glyphs never affect any pixels outside the pixel-snapped rectangle derived from the text's advance width, ascent and descent. That assumption is not true on Mac with subpixel rendering (and in general, for weird fonts, it's not true on any platform).

Comment 3

[Jesse Ruderman]

Is it guaranteed to be true if you stick 0.2em of padding in?

Comment 4

[Robert O'Callahan (:roc) (email my personal email if necessary)]

In theory? No. In practice? Yes.

Comment 5

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

Comment on attachment 336318 [details] [diff] [review]
fix

r+sr=dbaron if you fix the 430813 tests by making the text transparent rather than introducing padding

Comment 6

[Robert O'Callahan (:roc) (email my personal email if necessary)]

(In reply to comment #5)
> r+sr=dbaron if you fix the 430813 tests by making the text transparent rather
> than introducing padding

But if I make the test transparent, then the test isn't testing anything because incorrect positioning of that last DIV won't cause a visual difference.

Comment 7

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

Can you put the padding on an inline containing the text, then, rather than on the block?  (And use line-height if you need vertical padding.)

Comment 8

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Attachment: fix v2

That works.

Comment 9

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

Comment on attachment 343301 [details] [diff] [review]
fix v2

r+sr=dbaron

Comment 10

[Robert O'Callahan (:roc) (email my personal email if necessary)]

Pushed 8735bfaf0b43