[ENH] HeatMap: Allow setting the center when using diverging palettes

[janezd]

Issue

Resolves #4789.

Includes

• Code changes
• Tests
• Documentation

[codecov]

Codecov Report

Merging #4809 into master will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4809      +/-   ##
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- Coverage   84.01%   84.01%   -0.01%     
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  Files         281      276       -5     
  Lines       56899    56140     -759     
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- Hits        47805    47165     -640     
+ Misses       9094     8975     -119     

[Hrovatin]

This seems to work.
However, as the centering window shows only after the diverging palette is chosen this might be hard to find for new users. Other heatmap GUI options seem to be always shown, but do not allow selection/changes if they would not make sense. Maybe the same could be done for the Center at field; e.g. grayed out if non-diverging palette is selected.
Also, other GUI options seem to be aligned more to the left, while Center at is aligned to the right. There could also be a bit more space between Center at and palette selector.

[janezd]

However, as the centering window shows only after the diverging palette is chosen this might be hard to find for new users. Other heatmap GUI options seem to be always shown, but do not allow selection/changes if they would not make sense. Maybe the same could be done for the Center at field; e.g. grayed out if non-diverging palette is selected.

I wanted to minimize the height, which is already large. The benefit of having a disabled checkbox would be to let the user know it is there, but it still wouldn't tell her how to enable it. What do you say about adding a hint, like in, say Confusion, that shows the first time the user opens the widget? Something like "For data with a 'base value', choose a diverging palette and set its center."

Also, other GUI options seem to be aligned more to the left, while Center at is aligned to the right. There could also be a bit more space between Center at and palette selector.

I wanted the opposite effect. :) I wanted to "tie" this option to the palette by aligning it to the right and putting it as close to palette as I could. If this intention is not clear, I should indeed align it to the left, like normal options.

Summary: I would keep hiding, but add a hint. I will align the checkbox to the left.

[ales-erjavec]

Optional[float]?

Also
centerChanged = Signal(float) needs to be changed to centerChanged = Signal(object)

[janezd]

Not really; Optional[float] would be equivalent to Union[float, None], while this was really Union[float, bool].

Terrible design. Now constructor gets either a float or None. In the latter case there is no centering, and it can't be re-enabled by changing center from None to float.

[Hrovatin]

If the Center at appears only for certain palettes then it is probably not that odd if it is located on the right, close to the palette selection box. (So left or right would be fine by me then.)

[janezd]

If the Center at appears only for certain palettes then it is probably not that odd if it is located on the right, close to the palette selection box. (So left or right would be fine by me then.)

OK, I prefer it on the right side. Moving back.