I think first we should clarify some more basic questions about subpixel
layout.
1. Is it actually mantained?
2. Do any port really need it?
Please correct me if these questions are too obvious or have been
resolved before. Note that I am not a fan of subpixel layout, neither an
enemy of it - in fact I do not know or care much about it. But from what
I know it seems like this is a feature that makes an essential
difference on the engine and I don't understand how can we allow such
huge divergence across WebKit ports. Isn't it a maintenance burden?
Doesn't it result in that test results across ports will diverge a lot more?
Br,
Balazs
On 07/31/2013 10:40 PM, Ryosuke Niwa wrote:
Can't we encounter the same bug if we you multiplied the same height
by 64 even if the sub pixel layout is not turned off? Or is there
some parser and other component that prevents such an overflow to happen?
- R. Niwa
On Wed, Jul 31, 2013 at 1:35 PM, Benjamin Poulain <[email protected]
<mailto:[email protected]>> wrote:
On Wed, Jul 31, 2013 at 4:34 AM, Javier Fernandez
<[email protected] <mailto:[email protected]>> wrote:
While looking into the bug #118595 I've found out that the
root cause
was an arithmetic overflow during the layout process, at least
in the
case of the WebKitGtk+ port, but I guess other ports have
similar root
cause. Notice that webkitgtk+ port enables the SUBPIXEL-LAYOUT
by default.
Later, I've concluded that the bug is not related to Regions
at all, but
something generic happening when the max-height CSS property
value is
set to a huge number. I've filled a new bug #119273 for this.
The arithmetic overflow is gone when enabling the
SATURATED_ARITHMETIC_LAYOUT flag, which actually, as far as I
could
understand, it's the purpose of such experimental feature.
However, I've provided a patch for the #119273 facing the
specific case
of the max-height. I don't think that's the right approach,
because I
think other CSS property might have the same problem, but I
thought it
was useful to understand the issue.
I think the right solution would be to enable the
SATURATED_ARITHMETIC_LAYOUT whenever the SUBPIXEL_LAYOUT flag is
enabled. Perhaps, eventually, both flags will become part of
the same
feature; that's one of the points to be discussed here.
I'm sending this email to this list in order to get an
agreement between
all the ports using the SUBPIXEL_LAYOUT feature, but perhaps
this should
be debated independently on each port's mailing list.
It looks to me like it is a good idea on the long term to have
saturated arithmetic enabled when you have subpixel layout.
I believe only GTK and EFL enable subpixel layout at the
moment(?). You can probably lead the way and mature the feature
and others will follow.
Cheers,
Benjamin
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