mix-blend-mode

[Malvoz]

Is mix-blend-mode useful? How does it compare to current use of opacity?

The following video showcases the different blend modes by applying the values to all .mapml-layer elements (I had to apply .leaflet-layer * {mix-blend-mode: inherit; } since it's not an inheritable property):

Static.Features.Test.-.mix-blend-mode.mp4

Other related CSS properties include: background-blend-mode and isolation.

Maybe options for changing blend modes could exist along with opacity in the UI, or otherwise we could have some documentation in web-map-docs for how to enable this.

[prushforth]

I am pretty certain this will be / is useful for cartographers, but I'm not an expert, especially when combining features within a single layer. I think this might also be relevant for user preferences, but not sure how we would enable it in a user interface easily, at least.

[Malvoz]

How does it compare to current use of opacity?

While opacity is simpler to work with, it's usage - which I believe is mainly to "blend" (wink wink) layers - causes the layer with reduced opacity to essentially be less visible. Conforming to WCAG success criteria for contrast (1.4.3 Contrast (Minimum), 1.4.6 Contrast (Enhanced), 1.4.11 Non-text Contrast) can be hard or even impossible depending on the applied opacity.

[Malvoz]

Opened an issue to discuss the Capability: Maps4HTML/HTML-Map-Element-UseCases-Requirements#247.

I'm closing this for now. We can revisit this at a later time if needed to satisfy user preferences, as suggested in #305 (comment).