[webkit-dev] Transformations precision: double -> float

[Stephen Chenney]

Ideally WebKit would avoid casts by consistently using either double or
floats everywhere a floating point representation is needed. I don't think
it's as simple as adding a typedef, but maybe it is. In any event it would
have to be spelled out in the style guide.

My gut feeling is that floats are enough for web layout, and map better
onto GPU back ends where bandwidth (memory) really matters. Is there
anything in the specs that force one or the other, or both? Is there a
compelling web content scenario that demands double precision?

Stephen.

On Mon, May 21, 2012 at 1:37 PM, Ryosuke Niwa <rniwa at webkit.org> wrote:

> Maybe you can add a typedef in Platform.h to make it configurable? e.g.
> maybe you want to be able to use long double instead of regular double in
> the future.
>
> - Ryosuke
>
> On Mon, May 21, 2012 at 10:34 AM, Simon Fraser <simon.fraser at apple.com>wrote:
>
>> TransformationMatrix started out as floats, then got changed to doubles
>> in <http://trac.webkit.org/changeset/40761>
>>
>> This was done because on most hardware there is no penalty for using
>> doubles over floats, and provided a better match with our system APIs that
>> used doubles.
>>
>> I'd prefer to take a forward-looking stance here, and assume that in time
>> hardware will catch up.
>>
>> Simon
>>
>> On May 21, 2012, at 4:04 AM, Zoltan Herczeg wrote:
>>
>> > Hi,
>> >
>> > is there any reason why the transformations in WebKit use doubles? We
>> > could optimize some functions further with ARM SIMD if they would be
>> > floats. Is there any objection to make them float if the change would
>> have
>> > no other side effects except some rounding because of the lower
>> precision?
>> >
>> > Regards,
>> > Zoltan
>> >
>> >
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