[FEATURE] Legend.Item Transparency on Disabled

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?

[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