Support for "Plus Darker" and "Plus Lighter" blend modes

[iamcalledrob]

These two blend modes (Plus Darker, Plus Lighter) are very useful when building UI, in particular, for iOS -- yet they are missing in Compose Multiplatform.

The web now somewhat supports this kind of blending via css mix-blend-mode:

mix-blend-mode: plus-darker;
mix-blend-mode: plus-lighter;

Sidenote: I believe "Plus Darker" is also known as "Linear Burn"

Here's Figma's video showing the effect of this type of blending -- as you can see, this is necessary for building native looking UI for Apple platforms.

FigmaBlending.mp4

Alternatively, support for custom blend mode formulae might be even more versatile

More reading:

• Figma forum discussion
• [css-compositing-2] Remove or fix definition of plus-darker w3c/fxtf-drafts#447
• NSCompositingOperation.plusDarker
• How to achieve linear burn using Subtract and Invert
• Skia: Custom blend modes using SkBlender

[iamcalledrob]

I believe this may also be made possible via a shader if RuntimeEffect.makeForBlender() (skia: SkRuntimeEffect::makeBlender) was made available within Skiko -- it's conspicuously missing.

Skiko RuntimeEffect.kt
Skia SkRuntimeEffect::makeBlender