Re: [eigen] random thoughts -- we need more Gaels

[Benoit Jacob <jacob.benoit.1@xxxxxxxxx>]

2010/10/10 Christoph Keller <christoph-keller@xxxxxx>:
> i want to comment on that 'how-to-more-developers' problem. A while ago I
> wanted to use Eigen for my raytracer, that uses Ray-Packets.
> To make that work I needed SoA-support and comparisons using the
> Vector-instructions. Gael invested time to help me start developing some SoA
> support.
> Then we talked about adding comparisons. Eigen does not have those now. I
> did not really see what I could do to add them to Eigen (Nobody really
> commented on my patch, except that using an or-operator in float is not
> useful. At least the SSE-comparisons and the corresponding operators could
> have been added).
>
> Now I am just waiting until someone else does the work. Something went wrong
> here.

This is a prime example of why we just moved to bugzilla for feature
discussions: with the mailing list, it's just too easy to forget about
patches and then it's hard to find them back. So, please understand
that we know about the organization problem you're talking about, and
we just addressed it! If you file a bug now, attach your patch and ask
for review, at least you should get a reply.

> My relativistic raytracer at http://www.wor.maxmus.de/ has some users now
> and it really bites, that it does not support any vector extension any more
> (I have stopped using SSE, because maintaining it was too much work). With
> AVX next year it will only become worse.
>
> I really want to have some sort of bool-the-size-of-scalar support, and I
> can also write it, but one has to decide how to do it (This does not belong
> in a plugin, and I do not want to rewrite my code later on).
>
> This should be something like
> template <class Scalar, int Booltype>
>
> Booltype can then support things like the highest bit decides if its
> true/false (useful for AVX to transform float to EigenBool<float,
> HighestBit> fast for example), or it has to be a bitmask etc ...
> After one has decided how to define this type adding functions like 'select'
> is quite easy ...

I actually agree with the general concept (as already said in that
mailing list thread).

The best thing you can do right now is file bugs for these features
that you want to see implemented, and let's continue the discussion as
comments on these bugs.

I also realize that the best thing _we_ can do is write more developer
documentation so you can be more effective writing Eigen code. By the
way (everyone) feel free to file bugs asking for developer
documentation covering _specific_ topics to we can make an informed
decision about what docs to write first.

Benoit

>
> Greetings,
> Christoph
>
>
>