fix scaling being read during running export job

[zisoft]

During a running export job the image scaling factor is read from the GUI/settings for each exported image, resulting in different export sizes if the scaling factor is changed.

fixes #18927

Steps to reproduce:

• select 10 images in lighttable
• start export to disk
• during the running export switch to scaling in the export module and change the scale factor

[TurboGit]

@zisoft : I had registered this for 5.2 and finally I would prefer to move this to 5.4. There is almost no chance to get field testing at this stage, this is a "corner" case so I'd like to stay on the safe side. Is that ok to you?

[fiascolemlaw]

I would politely suggest this issue is a little more than a corner case. I’m was quite surprised to not find it as an already logged issue, though this fact does not give weight to my argument that this is more than a corner case. Seems it must be an incredibly common requirement. As it stands anyone who wants to do an export of any mixture of aspect ratios and/or portrait or landscape images in anything other than one fixed width or height cannot do so without babysitting their export jobs and triggering them manually one by one.

I would love to see this make it into 5.2, but appreciate and defer to you guys, who understand the risks of rushing this better than me, to make the most prudent decision on whether this has to wait until 5.4.

If it helps I can try and build from source tomorrow to act as an extra tester.

[TurboGit]

@fiascolemlaw : Yes please test, not saying that we will merge this in 5.2, but without testing it won't be merged anyway. Note that there is many files impacted, so we want to merge quite a lot the export module to ensure we properly export depending on all settings.

We also want to test the print module and the thumbs generation.

As I said, this is not a simple change to me.

[zisoft]

Fully agreed @TurboGit. Too risky just a week before release.

[zisoft]

@fiascolemlaw:

As it stands anyone who wants to do an export of any mixture of aspect ratios and/or portrait or landscape images in anything other than one fixed width or height cannot do so without babysitting their export jobs and triggering them manually one by one.

Have you tried setting width AND height to the same pixel value, i.e. 2000 x 2000 ?

In this case you won't get a square export, darktable now takes the longest side (either height or width) and keeps the aspect ratio. So for a mix of portraits and landscapes you get all images to be either 2000px high or 2000px wide.