sign problem with shear angle in transform matrix

[Regina Henschel]

Hi Armin,

Armin Le Grand schrieb am 22-Jan-20 um 18:13:

> 
> Interesting - so they do the same thing and let it look like the 
> coordinate system we all know from school and that rotates 
> counterClockWise - a good argument to mabe just stay with that in the 
> files. But that raises a problem with the full matrix we do not write 
> but can read from ODF - there, the rotation is correct AFAIK (not sure 
> about Shear...)

I have assumed in SdXMLImExTransform2D::GetFullTransform(), that the 
matrix() value in file format gives mathematically correct matrix. That 
is the current handling in case IMP_SDXMLEXP_TRANSOBJ2D_MATRIX already. 
I have not found any application, that actually writes it, so could not 
test this assumption. But it makes sense to treat it as mathematically 
correct.

> 
> No. I did by purpose not change that in aw080. But we might/should 
> comment it.

Agree, better documentation is needed. Same for the API property 
TransformationInHoriL2R

> 
> With the MS case above, maybe we should go the other way and use 
> left-handes AKA MS AKA ccw-oriented just everywhere - in ODF

In ODF we have already different orientations, so ODF needs to specify 
the orientation in each single case.

  and UNO
> API? That would at least be consequent and maybe easier to achieve (if 
> at all) as the other way round. I am just not sure if we would run into 
> problems with linear combinations - matrix multiplication and 
> changing/correcting the orientation are not commutative AFAIK...

Yes multiplication will not work. In 
SdrObjCustomShape::AdjustToMaxRect() I decompose the matrix from 
TRGetBaseGeometry, compose a mathematically correct one, do my 
transformations, decompose the result and compose a matrix suitable for 
TRSetBaseGeometry.

If the 'wrong' shear angle of the matrix in 
TRGetBaseGeometry/TRSetBaseGeometry will not be corrected, then it 
should be documented, perhaps in include/svx/svdobj.hxx. When I worked 
on AdjustToMaxRect(), it took me a while to realize that the wrong shear 
angle was the reason that it didn't work as expected.

Kind regards
Regina