Corrected dimensions while exporting

[jenshannoschwalm]

Depending on pipe.processed_width&height and the given width&height from the export dialog the dimensions for the pixelpipe run could be too small due to flooring.

Instead we do rounding here for the processed width&height and afterwards recalculate the scale to
a) be sure there are no pixels missing
b) avoid out-of-bounds problems.

One report about such rounding errors is in #16689

To reproduce you can take any raw with a size of at least 8288x5520 pixels and crop the size to exactly that in rawprepare while watching the dimensions in the "Image information" section.
darktable -d pipe -d imageio will report the dimension as here

94,1707 [dt_imageio_export] [export] imgid 7871, 8288x5520 --> 1532x1020 (scale 0,1848). upscale=no, hq=yes

keeping at least one dimension for what we want.

This is a tricky part of the pipeline and we had a number of issues related to export dimensions so please test in depth - i did so and couldn't spot anything wrong - watching out for

1. artifacts at the outermost pixels right and bottom
2. wrong sizes

So hopefully
Fixes #16689
Fixes #16638
Also seems good for #16133

without introducing a regression.

If good the release note would simply be "Fixed exported image dimensions"

[jenshannoschwalm]

I know that this has been discussed years ago in #3757 but as we have things fixed in finalscale and the interpolator i thinks it's fine to re-evaluate.

[jenshannoschwalm]

Updated comments about old issues, don't ceil but round.

Tested all of that old issues and current ones, seems good to me now.

[TurboGit]

I'm not sure for all cases, but there is still issues and it is hard to evaluate if more cases are better covered with this PR.

For example, take the integration test image mire1.cr2. The original size is 3908 x 2602.

Edit it in darkroom and do a square crop taking the whole height (2602 x 2602). Now export with 1920 x 1920 in export module. On my side I get an image of 1920 x 1919.

Now back to crop and resize the crop area to have an even size, for example 2104 x 2104. Again export and you'll get an image of size 1920 x 1919.

Back again to crop and resize the crop area to have an odd size, for example 2565 x 2565. Again export and you'll get an image of size 1920 x 1920.

Also, do a crop size 1917 x 1917, export and you'll get 1916 x 1916.

I found out that even/odd if not really a parameter but more the actual crop size. As I said I'm not sure how to get this right in all cases, a very hard issue to fix to me as the pixelpipe is handled.

[jenshannoschwalm]

Will investigate further next week

[jenshannoschwalm]

Closing this, pending work will be based on #16748