[webkit-dev] Should SATURATED_ARITHMETIC_LAYOUT be forced when enabling SUBPIXEL_LAYOUT ?

[Ryosuke Niwa]

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 <benjamin at webkit.org>wrote:

> On Wed, Jul 31, 2013 at 4:34 AM, Javier Fernandez <jfernandez at igalia.com>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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