Re: comments on Matrix

On Wed, Mar 20, 2013 at 4:32 PM, Dean Jackson <dino@apple.com> wrote:

>
> On 21/03/2013, at 10:25 AM, Benoit Jacob <jacob.benoit.1@gmail.com> wrote:
>
>
>
> 2013/3/20 Rik Cabanier <cabanier@gmail.com>
>>
>>  and hearing that some of these mistakes are copied from other,
>>> already-blessed Web APIs is even more discomforting.
>>>
>>
>> What you call a mistake (QR decomposition) is a well documented, fast
>> alternative (I know at least 3 now that use this).
>> From the paper you quoted:
>>
>> Also, the algorithms for QR are simple and efficient. The drawback is
>> that the orthogonal matrix
>> extracted is not particularly meaningful: it is not independent of the
>> coordinate basis used, and so has no
>> “physical” significance
>>
>>
>> This implies that the QR algorithm is fast but it doesn't produce results
>> that you should use directly.
>> So, we should use it for matrix interpolation but not to get the
>> decomposed values out.
>>
>
> That's not what I get from this quote. This is saying that QR
> decomposition is simple and efficient to perform, but is not going to give
> good results for matrix interpolation, since that should definitely be
> coordinate-independent and "physically meaningful".
>
>
> FWIW, this is the algorithm that CSS transforms uses for matrix
> interpolation (via decomposition). It's also the same as Core Animation. We
> have not had anyone complain about physical meaninglessness. We have had
> one person request interpolation purely by indices, which is definitely
> meaningless. The goal was to have something that looks "correct" the vast
> majority of times.
>
>
Yes, Flash and some of our tools also use this algorithm and AFAIK it works
fine.