[ENH] Error Animations

[irgolic]

Issue

Resolves #3377, #3699

Description of changes

Using QPropertyAnimation and an opacity property, makes warnings and errors flash on update.

In nodeitem.py, GraphicsIconItem now subclasses QGraphicsWidget instead of QGraphicsItem (to allow QPropertyAnimation). I've not tested this change extensively, and am not aware of its implications.

Includes

• Code changes
• Tests
• Documentation

[irgolic]

Some widgets call update when clicking any button/slider in the widget window, but some (due to the error/warning) completely suppress it.

An example of this is File (titanic) -> Scatterplot, where Scatterplot displays a warning but does not animate it upon interacting with the window.

Is there a way to enable such behavior for all widgets, or would each individual widget behaving this way have to be changed?

[codecov]

Codecov Report

Merging #3788 into master will increase coverage by 0.07%.
The diff coverage is 78.57%.

@@            Coverage Diff             @@
##           master    #3788      +/-   ##
==========================================
+ Coverage   84.97%   85.04%   +0.07%     
==========================================
  Files         374      374              
  Lines       69088    69122      +34     
==========================================
+ Hits        58709    58787      +78     
+ Misses      10379    10335      -44

[janezd]

Funny, I just started typing a similar comment about inconsistent behaviour of widgets.

This is not easy to fix. The logic of clearing and showing error messages is rather complex. Some widgets clear errors on receiving new data and then re-show them in set_data or related functions. Others do it when udpating the scene or the output. And some do it in callbacks, thus anywhere. This will never be uniform.

[janezd]

We discussed this at the meeting: we like flashing, but perhaps five times instead of just two.

It is not nice that errors are not re-animated or that they will sometimes be reanimated without obvious reason, but we can live with it.

[irgolic]

I think flashing 5 times might be a bit excessive. I've pushed an example, what do you think?
The errors' visibility is increased with flashing, but it helps less with warnings due to their bright color.

Also, where are general informative messages used (not warnings/errors), should those flash too?

[janezd]

Info: I guess not.

I'll check the new commit tomorrow.

[janezd]

I will merge the PR so everybody will the change and comment. :) We can easily decrease the number of flashes (yes, it is a bit too much :)) later.