Non-modal errors via background painting

[jdpurcell]

Similar to #649 but overrides MainWindow::paintEvent to display the error message. Fixes #387.

[vassudanagunta]

looks great! You should add "fixes #387" to the description.

[jurplel]

Really smooth and far less code change than #649 (not that the work wasn't great there)

[fkubicek]

Let's go! :) Your version works great for me.

[fkubicek]

I was messing around some more with it and I discovered an issue: in fullscreen mode with titlebar enabled, it's not rendered properly:

As you can (barely - that's the problem) see, there's no background for the text. I had some trouble with this when I was working on the other PR, so maybe you could use my solution from there. (Not sure how copy-paste-able it is.)

Also, both in normal and fullscreen modes, this line

is transparent and changes color with the background. But I'm not sure whether it's related to this PR.

I apologise for not making a proper Issue or PR, I don't have much time these days, just thought I would post my findings here.

[jdpurcell]

I was messing around some more with it and I discovered an issue: in fullscreen mode with titlebar enabled, it's not rendered properly

Oops! Thanks for testing and reporting. I know how to fix this, the original implementation in my fork handled this fine in fact, but I made a small modification for this PR that broke it. I'll submit another PR tonight to correct it.

Also, both in normal and fullscreen modes, this line is transparent and changes color with the background. But I'm not sure whether it's related to this PR.

Not sure either as I cannot reproduce (EDIT: I reproduced it later on a different machine), but if it is related, the fix for the first issue would likely correct this as well.

[jurplel]

Can you also verify the text appears on any background color, including the absence of a background color in both dark and light shell settings?

[jdpurcell]

Can you also verify the text appears on any background color, including the absence of a background color in both dark and light shell settings?

Yes! That's handled by the getPerceivedBrightness function, which analyzes the background color of the viewport (no matter whether it's from the user's custom settings, or if none is specified, the painter's background color i.e. the window default). It then chooses white or black text for the error message accordingly to ensure maximum readability. Credit and thanks again to @fkubicek for this idea.

If you still have macOS you can even try disabling the custom background color, loading a file that errors, and toggling the OS's dark mode on and off. qView responds instantly to the change redrawing both the background and error message with the appropriate colors.

[jurplel]

Can you also verify the text appears on any background color, including the absence of a background color in both dark and light shell settings?

Yes! That's handled by the getPerceivedBrightness function, which analyzes the background color of the viewport (no matter whether it's from the user's custom settings, or if none is specified, the painter's background color i.e. the window default). It then chooses white or black text for the error message accordingly to ensure maximum readability. Credit and thanks again to @fkubicek for this idea.

If you still have macOS you can even try disabling the custom background color, loading a file that errors, and toggling the OS's dark mode on and off. qView responds instantly to the change redrawing both the background and error message with the appropriate colors.

Perfect!