A sky on a Jetpack Composable Function (yes, you read it right)

Sky.kt

import android.graphics.RuntimeShader
import android.os.Build.VERSION_CODES
import androidx.annotation.RequiresApi
import androidx.compose.animation.core.withInfiniteAnimationFrameMillis
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.produceState
import androidx.compose.ui.Modifier
import androidx.compose.ui.composed
import androidx.compose.ui.draw.drawWithCache
import androidx.compose.ui.graphics.ShaderBrush
import androidx.compose.ui.graphics.drawscope.withTransform
import androidx.compose.ui.tooling.preview.Preview

@RequiresApi(VERSION_CODES.TIRAMISU)
@Preview
@Composable
fun Sky() = Box(modifier = Modifier.fillMaxSize().composed {
    val time by produceState(0f) {
        while (true) { withInfiniteAnimationFrameMillis { value = it / 1000f } }
    }
    Modifier.drawWithCache {
        val shader = RuntimeShader(
            """
                uniform float2 iResolution;      // Viewport resolution (pixels)
                uniform float  iTime;            // Shader playback time (s)

                const float cloudscale = 1.1;
                const float speed = 0.03;
                const float clouddark = 0.5;
                const float cloudlight = 0.3;
                const float cloudcover = 0.2;
                const float cloudalpha = 8.0;
                const float skytint = 0.5;
                const vec3 skycolour1 = vec3(0.2, 0.4, 0.6);
                const vec3 skycolour2 = vec3(0.4, 0.7, 1.0);

                const mat2 m = mat2( 1.6,  1.2, -1.2,  1.6 );

                vec2 hash( vec2 p ) {
                    p = vec2(dot(p,vec2(127.1,311.7)), dot(p,vec2(269.5,183.3)));
                    return -1.0 + 2.0*fract(sin(p)*43758.5453123);
                }

                float noise( in vec2 p ) {
                    const float K1 = 0.366025404; // (sqrt(3)-1)/2;
                    const float K2 = 0.211324865; // (3-sqrt(3))/6;
                    vec2 i = floor(p + (p.x+p.y)*K1);
                    vec2 a = p - i + (i.x+i.y)*K2;
                    vec2 o = (a.x>a.y) ? vec2(1.0,0.0) : vec2(0.0,1.0); //vec2 of = 0.5 + 0.5*vec2(sign(a.x-a.y), sign(a.y-a.x));
                    vec2 b = a - o + K2;
                    vec2 c = a - 1.0 + 2.0*K2;
                    vec3 h = max(0.5-vec3(dot(a,a), dot(b,b), dot(c,c) ), 0.0 );
                    vec3 n = h*h*h*h*vec3( dot(a,hash(i+0.0)), dot(b,hash(i+o)), dot(c,hash(i+1.0)));
                    return dot(n, vec3(70.0));
                }

                float fbm(vec2 n) {
                    float total = 0.0, amplitude = 0.1;
                    for (int i = 0; i < 7; i++) {
                        total += noise(n) * amplitude;
                        n = m * n;
                        amplitude *= 0.4;
                    }
                    return total;
                }

                // -----------------------------------------------

                vec4 main(in vec2 fragCoord) {
                    vec2 p = fragCoord.xy / iResolution.xy;
                    vec2 uv = p*vec2(iResolution.x/iResolution.y,1.0);
                    float time = iTime * speed;
                    float q = fbm(uv * cloudscale * 0.5);

                    //ridged noise shape
                    float r = 0.0;
                    uv *= cloudscale;
                    uv -= q - time;
                    float weight = 0.8;
                    for (int i=0; i<8; i++){
                        r += abs(weight*noise( uv ));
                        uv = m*uv + time;
                        weight *= 0.7;
                    }

                    //noise shape
                    float f = 0.0;
                    uv = p*vec2(iResolution.x/iResolution.y,1.0);
                    uv *= cloudscale;
                    uv -= q - time;
                    weight = 0.7;
                    for (int i=0; i<8; i++){
                        f += weight*noise( uv );
                        uv = m*uv + time;
                        weight *= 0.6;
                    }

                    f *= r + f;

                    //noise colour
                    float c = 0.0;
                    time = iTime * speed * 2.0;
                    uv = p*vec2(iResolution.x/iResolution.y,1.0);
                    uv *= cloudscale*2.0;
                    uv -= q - time;
                    weight = 0.4;
                    for (int i=0; i<7; i++){
                        c += weight*noise( uv );
                        uv = m*uv + time;
                        weight *= 0.6;
                    }

                    //noise ridge colour
                    float c1 = 0.0;
                    time = iTime * speed * 3.0;
                    uv = p*vec2(iResolution.x/iResolution.y,1.0);
                    uv *= cloudscale*3.0;
                    uv -= q - time;
                    weight = 0.4;
                    for (int i=0; i<7; i++){
                        c1 += abs(weight*noise( uv ));
                        uv = m*uv + time;
                        weight *= 0.6;
                    }

                    c += c1;

                    vec3 skycolour = mix(skycolour2, skycolour1, p.y);
                    vec3 cloudcolour = vec3(1.1, 1.1, 0.9) * clamp((clouddark + cloudlight*c), 0.0, 1.0);

                    f = cloudcover + cloudalpha*f*r;

                    vec3 result = mix(skycolour, clamp(skytint * skycolour + cloudcolour, 0.0, 1.0), clamp(f + c, 0.0, 1.0));

                    return vec4( result, 1.0 );
                }
            """
        )
        val shaderBrush = ShaderBrush(shader)
        shader.setFloatUniform("iResolution", size.width, size.height)
        shader.setFloatUniform("iTime", time)
        onDrawBehind {
            withTransform({ scale(scaleX = 1f, scaleY = -1f) }) {
                drawRect(shaderBrush)
            }
        }
    }
})