drive overscroll from the factory, fix the gradient height, share the bar colour

app/src/main/kotlin/com/subtracks/ui/components/StretchOverscroll.kt

@@ -4,93 +4,108 @@ import androidx.compose.animation.core.Animatable
 import androidx.compose.animation.core.Spring
 import androidx.compose.animation.core.spring
 import androidx.compose.foundation.LocalOverscrollFactory
+import androidx.compose.foundation.OverscrollEffect
+import androidx.compose.foundation.OverscrollFactory
 import androidx.compose.foundation.layout.Box
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.CompositionLocalProvider
-import androidx.compose.runtime.remember
+import androidx.compose.runtime.mutableFloatStateOf
-import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.geometry.Offset
-import androidx.compose.ui.graphics.TransformOrigin
+import androidx.compose.ui.graphics.drawscope.ContentDrawScope
-import androidx.compose.ui.graphics.graphicsLayer
+import androidx.compose.ui.graphics.drawscope.scale
-import androidx.compose.ui.input.nestedscroll.NestedScrollConnection
+import androidx.compose.ui.graphics.drawscope.translate
 import androidx.compose.ui.input.nestedscroll.NestedScrollSource
-import androidx.compose.ui.input.nestedscroll.nestedScroll
+import androidx.compose.ui.node.DelegatableNode
+import androidx.compose.ui.node.DrawModifierNode
 import androidx.compose.ui.unit.Velocity
-import kotlinx.coroutines.launch
 import kotlin.math.abs
 
 private const val MAX_STRETCH_FRACTION = 0.30f
 
+private object StretchOverscrollFactory : OverscrollFactory {
+    override fun createOverscrollEffect(): OverscrollEffect = StretchOverscrollEffect()
+
+    override fun hashCode(): Int = 0x5EED_5EED
+
+    override fun equals(other: Any?): Boolean = other is StretchOverscrollFactory
+}
+
+private class StretchOverscrollEffect : OverscrollEffect {
+    private val overscroll = mutableFloatStateOf(0f)
+
+    private val drawNode =
+        object : Modifier.Node(), DrawModifierNode {
+            override fun ContentDrawScope.draw() {
+                val raw = overscroll.floatValue
+                if (raw == 0f) {
+                    drawContent()
+                    return
+                }
+                val limit = size.height * MAX_STRETCH_FRACTION
+                val capped = raw.coerceIn(-limit, limit)
+                val resisted = capped / (1f + abs(capped) / (size.height * 0.5f))
+                val pivot = Offset(size.width / 2f, if (resisted > 0f) 0f else size.height)
+                scale(scaleX = 1f, scaleY = 1f + abs(resisted) / size.height, pivot = pivot) {
+                    translate(left = 0f, top = resisted) {
+                        this@draw.drawContent()
+                    }
+                }
+            }
+        }
+
+    override val node: DelegatableNode get() = drawNode
+
+    override val isInProgress: Boolean get() = overscroll.floatValue != 0f
+
+    override fun applyToScroll(
+        delta: Offset,
+        source: NestedScrollSource,
+        performScroll: (Offset) -> Offset,
+    ): Offset {
+        if (delta.y == 0f) return performScroll(delta)
+        var remainingY = delta.y
+        if (overscroll.floatValue != 0f) {
+            val current = overscroll.floatValue
+            val next = current + remainingY
+            val clamped = if (current > 0f) next.coerceAtLeast(0f) else next.coerceAtMost(0f)
+            remainingY -= clamped - current
+            overscroll.floatValue = clamped
+        }
+        val consumed = performScroll(Offset(delta.x, remainingY))
+        val leftover = remainingY - consumed.y
+        if (leftover != 0f) {
+            val current = overscroll.floatValue
+            val next = current + leftover
+            overscroll.floatValue =
+                when {
+                    current > 0f -> next.coerceAtLeast(0f)
+                    current < 0f -> next.coerceAtMost(0f)
+                    else -> next
+                }
+        }
+        return Offset(consumed.x, delta.y)
+    }
+
+    override suspend fun applyToFling(
+        velocity: Velocity,
+        performFling: suspend (Velocity) -> Velocity,
+    ) {
+        if (overscroll.floatValue != 0f) {
+            Animatable(overscroll.floatValue).animateTo(0f, spring(stiffness = Spring.StiffnessMedium)) {
+                overscroll.floatValue = value
+            }
+        }
+        performFling(velocity)
+    }
+}
+
 @Composable
 fun StretchOverscroll(
     modifier: Modifier = Modifier,
     content: @Composable () -> Unit,
 ) {
-    val overscroll = remember { Animatable(0f) }
+    CompositionLocalProvider(LocalOverscrollFactory provides StretchOverscrollFactory) {
-    val scope = rememberCoroutineScope()
+        Box(modifier) { content() }
-
-    val connection =
-        remember(overscroll) {
-            object : NestedScrollConnection {
-                override fun onPreScroll(
-                    available: Offset,
-                    source: NestedScrollSource,
-                ): Offset {
-                    val current = overscroll.value
-                    if (current == 0f || available.y == 0f) return Offset.Zero
-                    val next = current + available.y
-                    scope.launch {
-                        overscroll.snapTo(if (current > 0f) next.coerceAtLeast(0f) else next.coerceAtMost(0f))
-                    }
-                    return available
-                }
-
-                override fun onPostScroll(
-                    consumed: Offset,
-                    available: Offset,
-                    source: NestedScrollSource,
-                ): Offset {
-                    val current = overscroll.value
-                    if (available.y == 0f) return Offset.Zero
-                    val next = current + available.y
-                    scope.launch {
-                        overscroll.snapTo(if (current > 0f) next.coerceAtLeast(0f) else next.coerceAtMost(0f))
-                    }
-                    return available
-                }
-
-                override suspend fun onPostFling(
-                    consumed: Velocity,
-                    available: Velocity,
-                ): Velocity {
-                    overscroll.animateTo(0f, spring(stiffness = Spring.StiffnessMedium))
-                    return available
-                }
-            }
-        }
-
-    CompositionLocalProvider(LocalOverscrollFactory provides null) {
-        Box(
-            modifier =
-                modifier
-                    .nestedScroll(connection)
-                    .graphicsLayer {
-                        val raw = overscroll.value
-                        if (raw == 0f) {
-                            scaleY = 1f
-                            translationY = 0f
-                        } else {
-                            val limit = size.height * MAX_STRETCH_FRACTION
-                            val capped = raw.coerceIn(-limit, limit)
-                            val resisted = capped / (1f + abs(capped) / (size.height * 0.5f))
-                            scaleY = 1f + abs(resisted) / size.height
-                            translationY = resisted
-                            transformOrigin = TransformOrigin(0.5f, if (resisted > 0f) 0f else 1f)
-                        }
-                    },
-        ) {
-            content()
-        }
     }
 }

app/src/main/kotlin/com/subtracks/ui/library/AlbumDetailScreen.kt

@@ -20,6 +20,7 @@ import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.navigationBars
 import androidx.compose.foundation.layout.offset
 import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.requiredHeight
 import androidx.compose.foundation.layout.statusBars
 import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.lazy.LazyColumn
@@ -136,7 +137,7 @@ fun AlbumDetailScreen(
 
                 var headerHeightPx by remember { mutableFloatStateOf(0f) }
                 var rowHeightPx by remember { mutableFloatStateOf(0f) }
-                var titleTopPx by remember { mutableFloatStateOf(0f) }
+                var titleBottomPx by remember { mutableFloatStateOf(0f) }
                 val scrollPx by remember {
                     derivedStateOf {
                         val index = listState.firstVisibleItemIndex
@@ -146,10 +147,10 @@ fun AlbumDetailScreen(
                 }
                 val barFraction by remember {
                     derivedStateOf {
-                        if (titleTopPx <= 0f || fadeDistancePx <= 0f) {
+                        if (titleBottomPx <= 0f || fadeDistancePx <= 0f) {
                             0f
                         } else {
-                            ((scrollPx - (titleTopPx - barHeightPx)) / fadeDistancePx).coerceIn(0f, 1f)
+                            ((scrollPx - (titleBottomPx - barHeightPx)) / fadeDistancePx).coerceIn(0f, 1f)
                         }
                     }
                 }
@@ -164,7 +165,7 @@ fun AlbumDetailScreen(
                     modifier =
                         Modifier
                             .fillMaxWidth()
-                            .height(maxHeight * GRADIENT_SCREENS)
+                            .requiredHeight(maxHeight * GRADIENT_SCREENS)
                             .offset { IntOffset(0, -scrollPx.roundToInt()) }
                             .alpha(gradientAlpha),
                 )
@@ -188,7 +189,10 @@ fun AlbumDetailScreen(
                                 onDownload = onDownload,
                                 onMore = onMore,
                                 topInset = statusBarDp,
-                                titleModifier = Modifier.onGloballyPositioned { titleTopPx = it.positionInParent().y },
+                                titleModifier =
+                                    Modifier.onGloballyPositioned {
+                                        titleBottomPx = it.positionInParent().y + it.size.height
+                                    },
                                 modifier = Modifier.onSizeChanged { headerHeightPx = it.height.toFloat() },
                             )
                         }
@@ -217,6 +221,18 @@ fun AlbumDetailScreen(
                         ).alpha(1f - barFraction),
                 )
 
+                Box(
+                    Modifier
+                        .align(Alignment.TopStart)
+                        .fillMaxWidth()
+                        .height(statusBarDp)
+                        .background(
+                            Brush.verticalGradient(
+                                listOf(Color.Black.copy(alpha = 0.55f), Color.Transparent),
+                            ),
+                        ).alpha(1f - barFraction),
+                )
+
                 TopAppBar(
                     title = {
                         Text(
@@ -236,7 +252,6 @@ fun AlbumDetailScreen(
                     modifier =
                         Modifier
                             .align(Alignment.TopStart)
-                            .background(Color.Black.copy(alpha = barFraction))
                             .clickable(
                                 interactionSource = remember { MutableInteractionSource() },
                                 indication = null,
@@ -264,7 +279,7 @@ private fun AlbumHeader(
         modifier =
             modifier
                 .fillMaxWidth()
-                .padding(start = 24.dp, end = 24.dp, top = topInset + 8.dp, bottom = 16.dp),
+                .padding(start = 24.dp, end = 24.dp, top = topInset + 24.dp, bottom = 16.dp),
         horizontalAlignment = Alignment.CenterHorizontally,
     ) {
         CoverArt(