[FEATURE] Legend.Item Transparency on Disabled

[seddonm1]

Current Behavior

When a user clicks on a legend item currently a strikethrough effect is placed through the text of that legend item and the coloured box of the legend item remains unchanged.

Possible Solution

I have done a quick proof-of-concept (which could easily be incorporated into the main repo) which changes the alpha channel on the existing box and text colours to increase the transparency.

The questions are:

• Is this feature considered useful by the community?
• If so, should there be additional configuration options exposed (preferred) so a user can provide dataset.disabledBackgroundColor, dataset.disabledBorderColor and legend.labels.disabledFontColor at the expense of adding additional configuration options or should it be guessed?

[etimberg]

@seddonm1 an interesting idea would be to add a single callback function that returns the styles to apply when disabled. This would mean that we wouldn't need to add a lot of different individual options. @simonbrunel thoughts?

[tucq88]

I think it's pretty useful as :

• Developers should make Charts UI align with system style for consistency, so they should able to change disable style to lower Opacity, adding icon... or just simple styling
• A callback is safer and easier for developers making custom changes, as providing options can't fit all cases

Currently there's only way allows us to change Legend style on filtering (as hidden) is to extend Legend, as well guided here, but this way need to copy a lot code from ChartJS core so it's not stable when core getting changed.

[etimberg]

This can be done by overriding the generateLabels callback. https://jsfiddle.net/1npmkjr6/1/

@kurkle not sure if we want that function to control the text colour as well

[kurkle]

Another option would be to implement the color as scriptable / label.

[etimberg]

If I wanted to make a ton of changes, I would do that and remove the LegendItem concept (same with tooltips) and replace with better contexts. Not sure that's worth it now