fix(iv): 'save window' saves only the visible region

[orelsin]

Issue: "Save Window As..." called ImageBuf::write() on the whole image, which made it do exactly the same thing as "Save As...".

Add IvGL::get_visible_image_roi(), which maps the two opposite corners, sorts out which is the min and which is the max, and intersects the result with the data window so only real pixels come back.
saveWindowAs() then writes ImageBufAlgo::cut() of that region instead of the whole buffer, returns an error if nothing is visible.

Closes #4716

Assisted-by: Claude Code / Claude Opus 5

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: orelsin / name: Aurele Boquet (6a7a1d3)

[lgritz]

Need CLA and formatting fix.

I built it on my side, and it did not behave quite like I expected.

Maybe we should establish a common understanding of what this does. What do you think is the difference between

• save as
• save window as
• save selection as

Trying them on my end, I could discern no difference at all. Now I'm a little confused about what we originally wanted and/or really should do.

I have some ideas, but before I pollute the space with my notions, I'd like to hear what you and others think.

What was your recipe for testing this? Do you have a sequence of actions that results in different saved results for the three menu choices?

[lgritz]

Wait! I take it back!

I was testing the wrong branch.

This does seem to work -- "save window as" does save the part of the image that's visible in the window as a separate image. So you can zoom, adjust window boundaries, etc., and it acts as a cropping tool.

[lgritz]

Seems to be failing CI.

[orelsin]

I had to rebase, there was a refactoring of IvGL which removed the variable m_current_image and replaced it with an image-slot array. I changed the cerr << statements to OIIO::print(stderr, ‘...’) and added the TODOs.

[lgritz]

LGTM, thanks!