Re: [geometry] DOMRect: use of unrestricted doubles

On Sun, Oct 16, 2016 at 9:21 PM, Simon Fraser <smfr@me.com> wrote:

> On Oct 16, 2016, at 9:34 AM, Rik Cabanier <cabanier@gmail.com> wrote:
>
> On Sat, Oct 15, 2016 at 2:47 PM, Simon Fraser <smfr@me.com> wrote:
>
>> https://drafts.fxtf.org/geometry/#DOMRect
>>
>> Using unrestricted doubles forces implementors to handle NaN and Inf
>> values for x, y, width and height, and to correctly propagate NaN and Inf
>> through steps used to calculate left, top, right, bottom (assuming IEEE
>> rules, though the spec does not make this explicit). This is non-trivial,
>> since std::min<> and  std::max<> do not follow the same NaN propagation
>> rules as Math.min()/Math.max(). Implementors have to add isnan() checks to
>> left, top, right, bottom implementations. Is the complexity worth it?
>>
>
> yes. We allowed this so NaN and Inf would signal when matrix calculations
> hit edge conditions.
> Instead of throwing or giving inaccurate result, it was decided to allow
> the values so authors can check for those. The alternative would be to
> throw and we feared that this would break a lot of code since people don't
> test with exceptions.
>
> See also the thread here: https://lists.mozilla.
> org/pipermail/dev-platform/2014-June/005091.html
>
> When I did the implementation in Firefox, this actually made the code
> easier to implement since I didn't have to add a bunch of conditionals and
> could just rely on the FPU to do the correct thing.
>
>
> Well, Firefox does the wrong thing for DOMRect.left() when, for example.
> width is NaN (if you assume the spec follows JS Math rules).
>

roc implemented DOMRect and it seems that it was a simple rename of
something that Firefox already had [1]. It likely doesn't follow the spec
to the letter.

There's a test in the patch in https://bugs.webkit.org/
> show_bug.cgi?id=163464 (which needs to be converted to a web platform
> test).
>

Why do you need to add the special case handling? If width or x is NaN,
shouldn't left always returns x?

1: https://bugzilla.mozilla.org/show_bug.cgi?id=916520
<https://bugzilla.mozilla.org/show_bug.cgi?id=916520>