AW: Consider translation of transformation matrix of image rotation

Hi Regina,

> It works in principle,
What does that mean ?!?

A: An empty constructed basegfx::B2DHomMatrix is on identity (no-op), so it is ideal to test if it 
is used. Will even work when usages add-up to identity matrix whant means 'no change'. Yes, use 
isIdentity() please.

B: You might calculate it, but it is not really needed. Since we rotate arouhd center (only) it is 
sufficient to extract rotation and set it - we know it's around center. The rest of the shape 
(svg:x/y/width/height) is the unrotated shape, so this is sufficient. It can be calculated to make 
error-checks if wanted. It will have to be calculated when someone will use more of the 
transformation later (or we do)

C: Not sure whant you mean here. Correcting the position means it's 'overdefined'. The 
(svg:x/y/width/height) and back-calculating from transformation with (-translate, rotate, 
translate) to rotate around center *should* always give the same center. If not, it is *not clear* 
which definition is the correct one. This is the reason the transformation should *not* contain 
positioning at all. The idea is: Apply (svg:x/y/width/height) first (pos and size), then apply 
transformation to it (rotate, shear, mirror (scale-1)).

HTH!

-----Ursprüngliche Nachricht-----
Von: Regina Henschel [mailto:rb.henschel@t-online.de] 
Gesendet: Friday, February 23, 2018 15:13
An: LO dev fdo <libreoffice@lists.freedesktop.org>
Cc: Armin Le Grand <Armin.LeGrand@extern.cib.de>
Betreff: Consider translation of transformation matrix of image rotation

Hi Armin, hi all,

this is about https://bugs.documentfoundation.org/show_bug.cgi?id=115590
and my proposal https://gerrit.libreoffice.org/#/c/50176/

It works in principle, but I'm not sure about some details:

A
It has a construction
     basegfx::B2DHomMatrix aFullTransform;

     with later on
     if ( !aFullTransform.isIdentity() )

Should I use
     basegfx::B2DHomMatrix aFullTransform;
     bool bHasTransformation;

     if ( bHasTransformation )
instead?

B
It has
     if ( aTransformedCenterPosition != aCenterPosition ) Is this check useful, or should I 
calculate the correction always, although the result might be the original value?

C
Is this the correct place at all to correct the position?

Kind regards
Regina