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

[Javier Fernandez]

Hi,

On 31/07/13 22:40, 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?
> 

For the specific case of max-height, if subpixel_layout is not enabled,
I think the LayoutUnit class will use the REPORT_OVERFLOW macro to spot
the issue during the CSS parsing stage; the LayoutUnit will call
MathExtras::clampTo on the initial CSS value.

Precisely, SATURATED_ARITHMETIC_LAYOUT, which requires SUBPIXEL_LAYOUT
support, is intended to protect the arithmetic operations, since the
initial values are already under control.

But, targeting your specific question, it would b possible to define a
maxh-height CSS Property value which does not overflow, hence
multiplying by 64 during the layout phase will spot the same bug, so the
answer to your specific question is: yes, the same bug will appear in
some cases even if subpixel_layout is not enabled.

Perhaps that's a interesting scenario to study, so I'll prepare some
test to verify whether I manage to reproduce the issue without
subpixel_layout support.

Regards,

--
Javi