Is there a composition local for the surface background color? ```private object MaterialRippleThem...

# compose

[ursus]

Is there a composition local for the surface background color?

private object MaterialRippleTheme : RippleTheme {

    @Composable
    override fun defaultColor() = RippleTheme.defaultRippleColor(
            contentColor = LocalContentColor.current,
            lightTheme = MaterialTheme.colors.isLight
        )

I see default ripples pick up content color via the LocalContentColor composition local.
I'd like to have my system pickup background color.

Is there a comp. local for that, or do I need to roll in my own?

[Alex Styl]

the color of surfaces can by changed by modifying your material theme. See MaterialTheme.colors.surface . The Surface composable uses the surface color and doesn't have any sort of background color.

AFAIK it is backed up by some sort of composition local (that's how material theme works under the hood)

what are you trying to achieve?

[ursus]

I dont want to change my surface backgrounds

Just the ripple over it, conditionally on surface color

[Alex Styl]

no such thing. you'd need to make your own

[Louis Pullen-Freilich [G]]

Just the ripple over it, conditionally on surface color (edited)

FWIW this is basically what content color is, surfaces provide content color based on background color, but the calculation lives at the surface level, rather than providing background color and then calculating this later. But it’s still ‘derived’ from background color

[ursus]

hmm no sure if I follow

Button is a surface, and a white button with blue text will give a blue ripple

[Louis Pullen-Freilich [G]]

Right, but by default the content color inside button is calculated from the background color, using contentColorFor

[Louis Pullen-Freilich [G]]

It’s also intended that text color / ripple color are the same, if you want it to be different then you would need to define a custom theme for the ripples

[ursus]

yes I want a custom theme for ripples, either white or black

but my designers chose to calculate it based on the background luminosity

and I was hoping to have a smart ripple theme globally in one place such that it would calculate the ripple color

so I dont have to provide it manually for any clickable surface

[Louis Pullen-Freilich [G]]

I guess my point is that it should be a responsibility of the surface to calculate and provide ripple colour, or else you will end up with an indirection where you need to provide background colour and separately calculate ripple colour based on that

[Louis Pullen-Freilich [G]]

E.g, there might be differences for light and dark theme, but you lose this information if you only provide a background colour. A dark background in light theme is different from a dark background in dark theme

[ursus]

right, but that means I need a MySurface?

[Louis Pullen-Freilich [G]]

Well, you would need that anyway because the background colour isn't provided in any case :)

[ursus]

right but none of the buttons and everything that builds on Surface wont work

[ursus]

oh well.. maybe I can just use contentColor luminosity to guesstimate if it needs white or black

[Louis Pullen-Freilich [G]]

Yeah, you would need to provide this colour at each component.

And yeah, in material (not material3) the content colour luminosity is used for this purpose, it's a pretty reasonable approximation

[Louis Pullen-Freilich [G]]

You'll still need to provide this RippleConfiguration for each component in any case, since this sort of global ripple customisation is not supported from 1.7 onwards

[ursus]

so overriding LocalRippleTheme is deprecated?

[Louis Pullen-Freilich [G]]

RippleTheme is deprecated yeah, take a look at:

https://developer.android.com/develop/ui/compose/touch-input/user-interactions/migrate-indication-ripple

[Louis Pullen-Freilich [G]]

I would say in general this use case falls a bit outside material supported customisation. Changing the ripple colour separately from text colour is very likely to run into cases where contrast ratios are bad, and you introduce accessibility issues

[ursus]

btw what is this about?

https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:compose/material/material/src/commonMain/kotlin/androidx/compose/material/Ripple.kt?q=RippleConfiguration&ss=androidx%2Fplatform%2Fframeworks%2Fsupport

that seems like a .. global configuration?

(that goes against the docs)

[ursus]

Screenshot_20240525-115938.png

[Louis Pullen-Freilich [G]]

Not really, I mean you can use it to provide global configuration but defining a static colour at the top level will be very broken :)

It's meant for per component overrides, like to disable a ripple on a particular button

[Louis Pullen-Freilich [G]]

It doesn't support derived theming or anything that would be helpful for global configuration

[ursus]

hmm you mean that I can't query LocalContentColor there?

[Louis Pullen-Freilich [G]]

Yeah, it's just a basic object you provide with a raw color