Resize against sizeElement, notViewElement

[gselzer]

Hi!

I've been dealing with examples over in pyapp-kit/scenex where, on the newest release of jupyter-rfb, my views cotinuously get smaller. I've tracked it down to a simple example, and the changeset here fixes things.

MCVE reproducing error:

1. Check out main:
2. uv run jupyter notebook examples/pygfx1.ipynb (with pygfx installed)
3. Run the existing cell, generating the canvas (tangentially, when I first run the canvas, it's all gray, but interacting with the canvas draws an image)
4. In a new cell, run:

disp.canvas.set_logical_size(400, 400)

5. In a new cell, run:

disp.canvas.get_logical_size()

Without these changes, it prints out (398.0, 398.0)

Through some Claude-assisted digging, it seems like this is because of this line in the CSS - removing this line makes the example print out (400.0, 400.0).

This PR instead changes the target of the BaseRenderView._resizeObserver to listen to the sizeElement instead of the viewElement, which takes the border out of play.

There are probably other ways to fix this - I don't have a comprehensive understanding of jupyter_rfb - so please feel free to suggest alternative fixes. I also don't know how to go about testing this fix, so pointers there would be appreciated.

[almarklein]

Thanks for the report and the suggested fix!

I took a different approach to fixing this, because it's important that the reported size matches the viewElement, because in GPU apis we want to know the exact physical size. I fixed it upstream in pygfx/renderview#16, I'll copy the code over to here soon.

[almarklein]

Oh crap, merged the wrong PR 😆 Anyway, I'll overwrite the same file soon.