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

Benjamin Poulain benjamin at webkit.org
Wed Jul 31 13:35:23 PDT 2013

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
> 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.

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