[FEATURE]: Add automatic contrast for secondary hover labels #8149

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1. Lexachoc

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   featuresomething newsomething new

   on Oct 27, 2026
2. camdecoster commented on Oct 27, 2026

   

   camdecoster

   on Oct 27, 2026

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   Thanks for opening this. @KoolADE85 will follow up with you on this.
3. camdecoster

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   enhancement

   P3backlogbacklog

   size: 1

   on Oct 27, 2026
4. KoolADE85 commented on Oct 27, 2026

   

   KoolADE85

   on Oct 27, 2026

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   I've been thinking about this one and how to avoid making the label just "black". It would be nice to have both the colour coding AND the contrast requirements.
   So, could we compare the label colour against the background colour and darken/lighten the label until it contrasts enough? In your screenshot, I envision the "Yellow Trace" label being a darker shade of yellow rather than black.
   I'd also want to ensure that we respect a user-supplied namecolor - even if it doesn't have good contrast.
5. Lexachoc commented on Oct 28, 2026

   

   Lexachoc

   on Oct 28, 2026

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   So, could we compare the label colour against the background colour and darken/lighten the label until it contrasts enough? In your screenshot, I envision the "Yellow Trace" label being a darker shade of yellow rather than black.

   I think this is feasible. We could maybe use a fixed-iteration binary search (perhaps just <= 5 iterations) to find a lighter or darker shade that meets the contrast while preserving the original hue.

   for(var i = 0; i < 5; i++) {
       // Binary search
   }

   My only concern is the potential performance impact, since this calculation would run during hover rendering.

   I'd also want to ensure that we respect a user-supplied namecolor - even if it doesn't have good contrast.

   Agreed! This was already the behavior in my original PR #8115. The automatic contrast adjustment only applies when namecolor is not explicitly specified, so user-supplied color is always respected.