Zoom scaling

[samuelallan72]

This adds a scale factor based on the screen dpi to scale the zoom size (make it work nicely on high and low dpi screens basically). Reference issue #1585.

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This change is 

[samuelallan72]

Hmm seems it messes up all the tests relating to zoom and hints...

[The-Compiler]

So I see various different issues here:

• The zoom values change on Travis with Xvfb, which I expect to be 96dpi?
• There are various places (sessions, hints, etc.) where the zoom factor is used but which are not adjusted right now.

As for the second point, if you agree I'd propose postponing this until after the refactoring I do in the qtwebengine branch, as then there should only be one location to change this - what do you think?

[samuelallan72]

The zoom scale should equal 1 at 96dpi, which wouldn't affect the tests in that case.

Yep, agree - that makes sense.

[The-Compiler]

The refactoring for QtWebEngine is mostly complete now, and all zooming happens via the AbstractZoom class now.

However, I think QtWebEngine will already adjust the zoom on highdpi, or at least it will with a qApp.setAttribute(Qt.AA_EnableHighDpiScaling) added to app.py - so it might only be necessary to do the adjustments in WebKitZoom.

@swalladge would you like to pick this up again?

[samuelallan72]

With the current git master, and QT_AUTO_SCREEN_SCALE_FACTOR=1 set in the environment, it seems to work perfectly well now. 100% zoom is normal size on my highdpi screens. It also seems consistent with both backends.

I don't think any zoom scaling is needed any more. :P Maybe the use of that environment variable should be put in the docs or faq if it isn't already?

[The-Compiler]

Even with the QtWebKit backend, right? Can you try adding qApp.setAttribute(Qt.AA_EnableHighDpiScaling) to app.py and see if it works without an environment variable then?

[samuelallan72]

Yep, even with QtWebKit. I just tried adding that line (to line 81 of app.py), but it didn't appear to change anything - with either backend or with/without the env variable.

[The-Compiler]

I referenced this from #1585 for now, and will take a closer look once I get my new laptop with a HighDPI screen. Thanks for the contribution though!

[The-Compiler]

So I just enabled Qt::AA_EnableHighDpiScaling in git master - I can't really test it yet (my highdpi laptop will finally arrive this or next week though, I hope...), but I'd love some feedback!

This should be equivalent to setting QT_AUTO_SCREEN_SCALE_FACTOR=1 FWIW and should at least scale stuff up with QtWebEngie.

[samuelallan72]

To be honest, I don't notice any difference, apart from the fact that it scales nicely without QT_AUTO_SCREEN_SCALE_FACTOR set now.

I find the scaling on my monitor slightly too much, so I set the default zoom to 80%. Your latest commits have also fixed the default zoom being applied to new pages as well. 👍