111526 - link focus outline (invert) invisible on gray backgrounds

Status: RESOLVED WORKSFORME

(Core Graveyard :: GFX, defect)

Description

[Jesse Ruderman]

The fix for bug 55676 made link focus visible on pages with black backgrounds, 
but didn't fix the problem for gray (#808080) backgrounds.

Several possible ways to fix this bug:

1. Instead of using "invert" to show link focus, use the color of text in the 
paragraph containing the link.  Text is black on most pages, always visible, 
and rarely the same color as links.

2. Make a new pseudocolor similar to "invert" that does something other than 
subtracting from #FFFFFF when the color is very close to #808080.

3. Change the meaning of "invert" as described in #2.  This seems to be within 
the spirit of the CSS spec, which emphasizes that "invert" is supposed to make 
the border visible.   From http://www.w3.org/TR/REC-CSS2/ui.html:

"The 'outline-color' accepts all colors, as well as the 
keyword 'invert'. 'Invert' is expected to perform a color inversion on the 
pixels on the screen. This is a common trick to ensure the focus border is 
visible, regardless of color background."

Comment 1

[Jesse Ruderman]

Attachment: testcase

Comment 2

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

->Compositor

Comment 3

[[e-mail]]

IE appears to suffer from the same problem, although the display is slightly
different because the outline appears above the text whereas Mozilla draws the
outline under the text (IMHO a bug).

If you change the meaning of invert, I suggest using an XOR with 0x808080.
This will provide a guaranteed level of contrast. If you want to see the effect
(Windows only) download my ghostly cursors from http://www.nrr.co.uk/win95/

Comment 4

[Kevin McCluskey (gone)]

Reassigning to dcone.

Comment 5

[Jesse Ruderman]

See also bug 56314, "reverse selection colors when page background is similar to
default selection background".

Comment 6

[Aaron Leventhal]

(In reply to comment #3)
> I suggest using an XOR with 0x808080. This will provide a guaranteed level of 
> contrast.

To do that, we'd need to change all of the InvertRect implementations in gfx,
for each OS.
For example:
http://lxr.mozilla.org/seamonkey/source/gfx/src/xlib/nsRenderingContextXlib.cpp#965
http://lxr.mozilla.org/seamonkey/source/gfx/src/windows/nsRenderingContextWin.cpp#2689

Am I understanding correctly that Cairo is going to become our new GFX backend
eventually? If so, will that apply to all/most of the platforms we support now,
and does it make sense to wait for Cairo before fixing this?

Comment 7

[Aaron Leventhal]

Tim, even though Cairo's far away, will it make this easier?

Comment 8

[Aaron Leventhal]

Masayuki, can your fix from bug 56314 be used to fix this?

Also, I'd like to be able to set a specific color for the outline, and have it
be changed only if there isn't sufficient difference with the background color.

Comment 9

[Masayuki Nakano [:masayuki] (he/him)(JST, +0900)(away 4/27 - 5/6)]

Umm.. I don't have good idea...

Comment 10

[Jesse Ruderman]

Firefox trunk now uses the text color for the focus outline rather than inverting the background color.  So a purple link on a gray background gets a purple focus outline.

This may change again; see bug 359497.