Matrix Animation

MatrixCompose.kt

import android.graphics.Typeface
import androidx.compose.foundation.Canvas
import androidx.compose.foundation.background
import androidx.compose.foundation.layout.BoxWithConstraints
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.Row
import androidx.compose.foundation.layout.RowScope
import androidx.compose.foundation.layout.fillMaxHeight
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.runtime.Composable
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.graphics.Paint
import androidx.compose.ui.graphics.drawscope.drawIntoCanvas
import androidx.compose.ui.graphics.nativeCanvas
import androidx.compose.ui.graphics.toArgb
import androidx.compose.ui.platform.LocalDensity
import kotlinx.coroutines.delay
import kotlin.random.Random

private val characters = listOf("ジ", "ェ", "ッ", "ト", "パ", "Z", "A", "R", "Q", "ッ", "ク", "構", "成", "I", "L", "N", "K", "8", "7", "C", "6")

@Composable
fun MatrixText(
    stripCount: Int = 20,
    modifier: Modifier = Modifier
) {
    Row(
        modifier = modifier.background(Color.Black)
    ) {
        for (columns in 0..stripCount) {
            MatrixColumn(
                Random.nextInt(8) * 1000L,
                (Random.nextInt(10) * 10L) + 100
            )
        }
    }
}

@Composable
fun RowScope.MatrixColumn(
    yStartDelay: Long,
    crawlSpeed: Long
) {
    BoxWithConstraints(
        modifier = Modifier
            .fillMaxHeight()
            .weight(1f)
    ) {
        val pxWidth = with(LocalDensity.current) { maxWidth.toPx() }
        val pxHeight = with(LocalDensity.current) { maxHeight.toPx() }

        val paint = Paint().asFrameworkPaint().apply {
            isAntiAlias = true
            textSize = pxWidth
            typeface = Typeface.SANS_SERIF
        }

        val matrixStrip =
            remember { Array((pxHeight / paint.textSize).toInt() + 1) { characters.random() } }
        val lettersToDraw = remember { mutableStateOf(Random.nextInt(matrixStrip.size)) }

        Canvas(
            modifier = Modifier
                .fillMaxHeight()
                .fillMaxWidth()
        ) {
            for (i in 0 until lettersToDraw.value) {
                val yPoint = i * paint.textSize

                if (i == lettersToDraw.value - 1) {
                    paint.color = 0xffcefbe4.toInt()
                } else {
                    paint.color = Color(0xff43c728)
                        .copy(alpha = i / lettersToDraw.value.toFloat())
                        .toArgb()
                }

                drawIntoCanvas {
                    it.nativeCanvas.drawText(matrixStrip[i], 0f, yPoint, paint)
                }
            }
        }

        LaunchedEffect(key1 = yStartDelay) {
            delay(yStartDelay)
            while (true) {
                lettersToDraw.value += 1
                if (lettersToDraw.value > matrixStrip.size) {
                    lettersToDraw.value = 0
                }
                if (lettersToDraw.value > matrixStrip.size * 0.5) {
                    // If we've drawn over half the strip, we can randomly change letters.
                    matrixStrip[Random.nextInt(lettersToDraw.value)] = characters.random()
                }
                delay(crawlSpeed)
            }
        }
    }
}

There is an improved version here https://gist.github.com/apkelly/c27bd3844f83ce7d3ecfe9804a613d84