On Jun 4, 2014, at 12:42 AM, Rik Cabanier <caban...@gmail.com> wrote:
>
>
>
> On Tue, Jun 3, 2014 at 3:29 PM, Robert O'Callahan <rob...@ocallahan.org>
> wrote:
> On Wed, Jun 4, 2014 at 10:26 AM, Rik Cabanier <caban...@gmail.com> wrote:
> That would require try/catch around all the "invert()" calls. This is ugly
> but more importantly, it will significantly slow down javascript execution.
> I'd prefer that we don't throw at all but we have to because SVGMatrix did.
>
> Are you sure that returning a special value (e.g. all NaNs) would not fix
> more code than it would break?
>
> No, I'm not sure :-)
> It is very likely that people are just calling invert and don't check for the
> exception. Returning NaN might indeed make thing more stable.
>
> I think returning all NaNs instead of throwing would be much better behavior.
>
> I completely agree.
> Going with Benoit's suggestion, we can change the idl for invert to:
> bool invert();
> and change inverse to return a matrix with NaN for all its elements.
I don’t think that this is really getting the point. You seem to have the
assumption that this is the most common pattern:
if (matrix.isInvertible())
matrix.invert();
It isn’t in browser engines and I don’t think it will be in web applications.
The actual use case would be to stop complex computations and graphical drawing
operations right away if the author knows that nothing will be drawn anyway.
function drawComplexStuff() {
if (matrix.isInvertible())
return; // Stop here before doing complex stuff.
… complex stuff...
}
There was an argument that:
if (matrix.isInvertible())
matrix.invert();
would force UAs to compute the determinant twice. Actually, UAs can be very
smart about that. The determinant is a simple double. It can be stored and
invalidated as needed internally. (If it even turns out to be an issue.)
I don't think that the argument about numerical stability counts either. If the
determinant is not exactly 0, then the matrix is invertible. It doesn’t really
matter if it is a result of numerical precision or not.
To get back to
bool invert()
DOMMatrix inverse()
invert() does a matrix inversion in place. So it is not particularly useful as
a simple check for singularity.
inverse() currently throws an exception. If it doesn’t anymore, then authors
need to know that they need to check the elements of DOMMatrix for NaN. On the
other hand, relying on exception checking isn’t great either.
Both is making the live more difficult for authors.
So I am not arguing that inverse() must throw and I dot argue that invert()
should return a boolean. Changing this is fine with me. I am arguing that
isInvertible() makes a lot of sense. Why wouldn’t it on the web platform if it
is useful in our engines? determinant() is a way to check for singularity.
Having either determinant() or isInvertible() or both makes a lot of sense to
me. determinant() will be used internally a lot anyway. Being smarter and store
the result of determinant() should solve some of the concerns.
Greetings,
Dirk
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