Gradient along a path using path.flatten in Compose, Inspired by William Candillon https://youtu.be/7SCzL-XnfUU, this uses Jetpack Compose to draw a gradient along a path https://github.com/wcandillon/can-it-be-done-in-react-native/tree/master/bonuses/skia-examples/src/PathGradient

GradientAlongPathAnimation.kt

package androidx.compose.samples.animationfactory

import androidx.compose.animation.core.Animatable
import androidx.compose.animation.core.infiniteRepeatable
import androidx.compose.animation.core.tween
import androidx.compose.foundation.Canvas
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.aspectRatio
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.layout.size
import androidx.compose.runtime.Composable
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.remember
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.geometry.Offset
import androidx.compose.ui.graphics.Brush
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.graphics.PathMeasure
import androidx.compose.ui.graphics.StrokeCap
import androidx.compose.ui.graphics.asAndroidPath
import androidx.compose.ui.graphics.lerp
import androidx.compose.ui.graphics.vector.PathParser
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp
import androidx.core.graphics.flatten
import kotlin.math.floor


/*
* Copyright 2022 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*     http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
 * Inspired by William Candillon https://youtu.be/7SCzL-XnfUU,
 * this uses Jetpack Compose to draw a gradient along a path
 * https://github.com/wcandillon/can-it-be-done-in-react-native/tree/master/bonuses/skia-examples/src/PathGradient
 */
@Composable
@Preview
fun GradientAlongPathAnimation() {
    val path = remember {
        HelloPath.path.toPath()
    }
    val bounds = path.getBounds()

    val totalLength = remember {
        val pathMeasure = PathMeasure()
        pathMeasure.setPath(path, false)
        pathMeasure.length
    }
    val lines = remember {
        path.asAndroidPath().flatten(0.5f)
    }
    val progress = remember {
        Animatable(0f)
    }
    LaunchedEffect(Unit) {
        progress.animateTo(
            1f,
            animationSpec = infiniteRepeatable(tween(3000))
        )
    }

    Box(modifier = Modifier.fillMaxSize()) {
        Canvas(modifier = Modifier
            .padding(top = 32.dp, start = 64.dp, bottom = 32.dp, end = 32.dp)
            .aspectRatio(bounds.width / bounds.height)
            .size(400.dp)
            .align(Alignment.Center),
            onDraw = {
                val currentLength = totalLength * progress.value
                lines.forEach { line ->
                    if (line.startFraction * totalLength < currentLength) {
                        val startColor = interpolateColors(line.startFraction, colors)
                        val endColor = interpolateColors(line.endFraction, colors)
                        drawLine(
                            brush = Brush.linearGradient(listOf(startColor, endColor)),
                            start = Offset(line.start.x, line.start.y),
                            end = Offset(line.end.x, line.end.y),
                            strokeWidth = 30f,
                            cap = StrokeCap.Round
                        )
                    }
                }
            })
    }
}

private val colors = listOf(
    Color(0xFF3FCEBC),
    Color(0xFF3CBCEB),
    Color(0xFF5F96E7),
    Color(0xFF816FE3),
    Color(0xFF9F5EE2),
    Color(0xFFBD4CE0),
    Color(0xFFDE589F),
    Color(0xFFFF645E),
    Color(0xFFFDA859),
    Color(0xFFFAEC54),
    Color(0xFF9EE671),
    Color(0xFF67E282),
    Color(0xFF3FCEBC)
)

private object HelloPath {
    val path = PathParser().parsePathString(
        "M13.63 248.31C13.63 248.31 51.84 206.67 84.21 169.31C140" +
                ".84 103.97 202.79 27.66 150.14 14.88C131.01 10.23 116.36 29.88 107.26 45.33C69.7 108.92 58.03 214.33 57.54 302.57C67.75 271.83 104.43 190.85 140.18 193.08C181.47 195.65 145.26 257.57 154.53 284.39C168.85 322.18 208.22 292.83 229.98 277.45C265.92 252.03 288.98 231.22 288.98 200.45C288.98 161.55 235.29 174.02 223.3 205.14C213.93 229.44 214.3 265.89 229.3 284.14C247.49 306.28 287.67 309.93 312.18 288.46C337 266.71 354.66 234.56 368.68 213.03C403.92 158.87 464.36 86.15 449.06 30.03C446.98 22.4 440.36 16.57 432.46 16.26C393.62 14.75 381.84 99.18 375.35 129.31C368.78 159.83 345.17 261.31 373.11 293.06C404.43 328.58 446.29 262.4 464.66 231.67C468.66 225.31 472.59 218.43 476.08 213.07C511.33 158.91 571.77 86.19 556.46 30.07C554.39 22.44 547.77 16.61 539.87 16.3C501.03 14.79 489.25 99.22 482.76 129.35C476.18 159.87 452.58 261.35 480.52 293.1C511.83 328.62 562.4 265.53 572.64 232.86C587.34 185.92 620.94 171.58 660.91 180.29C616 166.66 580.86 199.67 572.64 233.16C566.81 256.93 573.52 282.16 599.25 295.77C668.54 332.41 742.8 211.69 660.91 180.29C643.67 181.89 636.15 204.77 643.29 227.78C654.29 263.97 704.29 268.27 733.08 256"
    )
}

private fun interpolateColors(
    animationValue: Float,
    colorsInput: List<Color>,
): Color {
    if (animationValue == 1f) return colorsInput.last()

    val scaledAnimationValue = animationValue * (colorsInput.size - 1)
    val oldColor = colorsInput[scaledAnimationValue.toInt()]
    val newColor = colorsInput[(scaledAnimationValue + 1f).toInt()]
    val newScaledAnimationValue = scaledAnimationValue - floor(scaledAnimationValue)
    return lerp(start = oldColor, stop = newColor, fraction = newScaledAnimationValue)
}

Love the combination of color and “signature-like” animation. Feels very smooth and “welcoming.” Would fit right in to some splash/welcome screen to a social app.