Reimplement Scalebar

[westnordost]

Screen_recording_20250106_222520.mp4

Reimplementation of scalebar. Somewhat similar to the Google Maps one, only better :-)

• can be aligned horizontally to start, end, center or anything in-between (i.e. also layout direction aware)
• text size and style can be specified, defaults to labelSmall
• both scale bar and text have a consistent halo and color (defaults to material3 surface and onSurface)
• can show metric, imperial or both. Will select a reasonable default based on the user's locale or system setting (if applicable)
• automatically a (minimum) size is selected so that the text does not overlap with the scalebar. Setting a bigger size is fine, too

[github-actions]

Remaining comments which cannot be posted as a review comment to avoid GitHub Rate Limit

spotless

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[spotless] _{reported by reviewdog 🐶}

maplibre-compose/lib/maplibre-compose-material3/src/commonMain/kotlin/dev/sargunv/maplibrecompose/material3/controls/ScaleBar.kt

Lines 233 to 261 in ebf96d2

	private val METRIC_STOPS: List<Float> = listOf(
	0.1f,
	0.2f,
	0.5f,
	1f,
	2f,
	5f,
	10f,
	20f,
	50f,
	100f,
	200f,
	500f,
	1000f,
	2000f,
	5000f,
	10000f,
	20000f,
	50000f,
	100000f,
	200000f,
	500000f,
	1000000f,
	2000000f,
	5000000f,
	10000000f,
	20000000f,
	40000000f,
	)

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[spotless] _{reported by reviewdog 🐶}

maplibre-compose/lib/maplibre-compose-material3/src/commonMain/kotlin/dev/sargunv/maplibrecompose/material3/controls/ScaleBar.kt

Lines 264 to 293 in ebf96d2

	private val IMPERIAL_STOPS: List<Float> = listOf(
	0.1f,
	0.2f,
	0.5f,
	1f,
	2f,
	5f,
	10f,
	20f,
	50f,
	100f,
	200f,
	500f,
	1000f,
	2000f,
	1f * FEET_IN_MILE,
	2f * FEET_IN_MILE,
	5f * FEET_IN_MILE,
	10f * FEET_IN_MILE,
	20f * FEET_IN_MILE,
	50f * FEET_IN_MILE,
	100f * FEET_IN_MILE,
	200f * FEET_IN_MILE,
	500f * FEET_IN_MILE,
	1000f * FEET_IN_MILE,
	2000f * FEET_IN_MILE,
	5000f * FEET_IN_MILE,
	10000f * FEET_IN_MILE,
	20000f * FEET_IN_MILE,
	)

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[spotless] _{reported by reviewdog 🐶}

maplibre-compose/lib/maplibre-compose-material3/src/commonMain/kotlin/dev/sargunv/maplibrecompose/material3/util.kt

Line 26 in ebf96d2

"BZ", "LR", "MM",

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maplibre-compose/lib/maplibre-compose-material3/src/commonMain/kotlin/dev/sargunv/maplibrecompose/material3/util.kt

Line 28 in ebf96d2

"AS", "GU", "MH", "MP", "PR", "PW", "VI", //"WS",

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maplibre-compose/lib/maplibre-compose-material3/src/commonMain/kotlin/dev/sargunv/maplibrecompose/material3/util.kt

Lines 30 to 31 in ebf96d2

	"AG", "AI", "BM", "BS", "FK", "GB", "GD", "GG", "GI", "GS", "IM", "JE", "KN", "KY", "LC",
	"MS", "TC", "VG", "VC" -> {

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[spotless] _{reported by reviewdog 🐶}

maplibre-compose/lib/maplibre-compose-material3/src/commonMain/kotlin/dev/sargunv/maplibrecompose/material3/util.kt

Line 44 in ebf96d2

"en", "my", "sm" -> {

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maplibre-compose/lib/maplibre-compose-material3/src/desktopMain/kotlin/dev/sargunv/maplibrecompose/material3/util.desktop.kt

Lines 5 to 6 in ebf96d2

	internal actual fun scaleBareMeasurePreference(): ScaleBarMeasure? =
	null

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maplibre-compose/lib/maplibre-compose-material3/src/iosMain/kotlin/dev/sargunv/maplibrecompose/material3/util.ios.kt

Lines 5 to 6 in ebf96d2

	internal actual fun scaleBareMeasurePreference(): ScaleBarMeasure? =
	null

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[spotless] _{reported by reviewdog 🐶}

maplibre-compose/lib/maplibre-compose-material3/src/jsMain/kotlin/dev/sargunv/maplibrecompose/material3/util.js.kt

Lines 5 to 6 in ebf96d2

	internal actual fun scaleBareMeasurePreference(): ScaleBarMeasure? =
	null

[sargunv]

(I can also pick this up from here and wrap up Apple implementation and the primary/secondary thing if you'd like)

[westnordost]

I am currently looking into the yard+mile stuff

[sargunv]

these can be generated, something like:

private fun buildStops(mantissas: Set<Int>, exponents: IntRange) = buildList {
    for (e in exponents)
        for (m in mantissas)
            add(m.toDouble() * Math.pow(10.0, e.toDouble()))
}

private val METRIC_STOPS = buildStops(mantissas = setOf(1, 2, 5), exponents = -1..7)

[westnordost]

Looks quite ingenious! For me at least, this would introduce a readability problem however, as I find it quite hard to understand what would be the resulting list.

This is the sort of complexity where I'd say that this needs a test case. But then, at the end, it will probably not really be less lines of code.

But anyway, if you want to go ahead with this anyway, I don't mind much.

[sargunv]

For me at least, this would introduce a readability problem however, as I find it quite hard to understand what would be the resulting list.

I considered that, but I think it's mitigated with just a comment explaining it's based on scientific notation: m*10^e.

if you want to go ahead with this anyway, I don't mind much.

sure, I'll take care of it; just need to tweak the above pattern for the transition between feet/yards and miles.

[westnordost]

hmm, maybe the Measure should be an interface... experimenting with an implementation

[westnordost]

Alright, done! One thing I am a bit worried about is whether the ScaleBarMeasure .Metric etc. are still considered as @Stable by Compose. If they are not, then this would lead to the widget being recomposed every frame, even if nothing changed. (Because the List of stops might have changed)

See also https://developer.android.com/develop/ui/compose/performance/stability/fix#immutable-collections

Should this library made to depend on kotlinx.collections.immutable to fix this?

[sargunv]

One thing I am a bit worried about is whether the ScaleBarMeasure .Metric etc. are still considered as @stable by Compose.

Strong skipping should prevent that, right? We can also tag them with @Immutable

[westnordost]

I thought strong skipping is only for automatic lambda memoization?

The docs make it sound like I have to annotate the thing as @Stable to enable the .equals(...) check

If we just annotate it as @Immutable, we are handing out guarantees that are out of our control. (ScaleBarMeasure is not sealed, because it doesn't have to be, and to enable funny 1st of April measures 🤩)

https://knowyourmeme.com/memes/banana-for-scale

[sargunv]

separately, I'm tempted to experiment with https://github.com/kevincianfarini/alchemist to represent the length units and their conversion using their Length value class (like Duration); unsure if it'll be worth the extra dependency but I'll try it and see how it looks.

[sargunv]

If we just annotate it as @immutable, we are handing out guarantees that are out of our control.

ah yeah, I was thinking just our implementations should be @Immutable. But I don't know, with polymorphic parameters, does the compose runtime consider immutability of the actual value at runtime, or just the declared type?

The docs make it sound like I have to annotate the thing as @stable to enable the .equals(...) check

I think @Immutable is also considered a "stable" value by the compose compiler, not just @Stable.

I thought strong skipping is only for automatic lambda memoization?

https://developer.android.com/develop/ui/compose/performance/stability/strongskipping#when-skip

Strong Skipping is a mode available in the Compose compiler. When enabled, it changes the compiler's behavior in two ways:

• Composables with unstable parameters become skippable
• Lambdas with unstable captures are remembered

[westnordost]

Skippable: If the compiler marks a composable as skippable, Compose can skip it during recomposition if all its arguments are equal with their previous values.

Hmm okay, sounds like we are good(?)

[sargunv]

Hmm okay, sounds like we are good(?)

yup, object combined with referential equality means we should be fine even without @Immutable

[westnordost]

Screen_recording_20250108_014006.mp4

20 Megabananas!