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

[kui zheng]

Hi, I have the same questions. Using float,  It's easier to map to
OGLES2, Decrease memory usage and accelerated using ARM SIMD.
if you do profiling for CSS transformation/Animation, you'll find
TransformationMatrix hotspots that should be well optimized  using
NEON.

-Kuii

On Mon, May 21, 2012 at 6:55 PM, Stephen Chenney <schenney at chromium.org> wrote:
> 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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>>
>>
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