On Sat, Jun 7, 2014 at 9:38 PM, Benoit Jacob <jacob.benoi...@gmail.com>
wrote:
>
>
>
> 2014-06-07 12:49 GMT-04:00 L. David Baron <dba...@dbaron.org>:
>
> On Monday 2014-06-02 20:45 -0700, Rik Cabanier wrote:
>> > - change isIdentity() so it's a flag.
>>
>> I'm a little worried about this one at first glance.
>>
>> I suspect isIdentity is going to be used primarily for optimization.
>> But we want optimizations on the Web to be good -- we should care
>> about making it easy for authors to care about performance. And I'm
>> worried that a flag-based isIdentity will not be useful for
>> optimization because it won't hit many of the cases that authors
>> care about, e.g., translating and un-translating, or scaling and
>> un-scaling.
>>
>
> Note that the current way that isIdentity() works also fails to offer that
> characteristic, outside of accidental cases, due to how floating point
> works.
>
> The point of this optimizations is not so much to detect when a generic
> transformation happens to be of a special form, it is rather to represent
> transformations as a kind of variant type where "matrix transformation" is
> one possible variant type, and exists alongside the default, more optimized
> type, "identity transformation".
>
> Earlier in this thread I pleaded for the removal of isIdentity(). What I
> mean is that as it only is defensible as a "variant" optimization as
> described above, it doesn't make sense in a _matrix_ class. If we want to
> have such a variant type, we should call it a name that does not contain
> the word "matrix", and we should have it one level above where we actually
> do matrix arithmetic.
>
> Strawman class diagram:
>
> Transformation
> / | \
> / | \
> / | \
> / | \
> Identity Matrix Other transform types
> e.g. Translation
>
> In such a world, the class containing the word "Matrix" in its name would
> not have a isIdentity() method; and for use cases where having a "variant
> type" that can avoid being a full blown matrix is meaningful, we would have
> such a variant type, like "Transformation" in the above diagram, and the
> isIdentity() method there would be merely asking the variant type for its
> type field.
>
Note that DOMMatrix implements the following under the hood:
DOMMatrix
/ | \
/ | \
/ | \
/ | \
Identity 2D-Matrix 3D-Matrix
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