Re: Image transformations

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: emacs-devel@gnu.org
> Date: Tue, 25 Jun 2019 10:43:22 -0400
> 
> >> Part of the reason for my question above is to figure out if the
> >> implementation of the API is likely to have such matrix inversion
> >> code internally
> > How can we possibly know for sure, on all supported platforms?
> 
> I'm not looking for "know for sure", just for a general understanding of
> how things usually work.
> 
> >> (since it seems quite possible that sometimes one is
> >> preferable and sometimes the other).
> > I admit I don't see why we would have different preferences.
> 
> I'm asking about the other side of the API, i.e. not us but the
> implementors of Cairo, etc...
> 
> It's really just out of curiosity, not directly related to what our code
> should do: does the "inverse matrix" indicate that the Windows guys use
> "fundamentally" different algorithms than the Cairo guys, or just that
> inverting the matrix is considered "par for the course" because
> sometimes you need one and sometimes you need the other.

I'm not the right person to answer these questions, as I don't have
enough background and experience in this area.  I think the differences
reflect the different designs and mindsets of the relevant
environments, but that's just a guess.  Perhaps Yamamoto-san could
comment on the nature of these differences.