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.
Benoit
>
> -David
>
> --
> 𝄞 L. David Baron http://dbaron.org/ 𝄂
> 𝄢 Mozilla https://www.mozilla.org/ 𝄂
> Before I built a wall I'd ask to know
> What I was walling in or walling out,
> And to whom I was like to give offense.
> - Robert Frost, Mending Wall (1914)
>
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