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@@ -1,5 +1,8 @@
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package eu.kanade.presentation.components
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+import androidx.compose.foundation.gestures.FlingBehavior
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+import androidx.compose.foundation.gestures.Orientation
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+import androidx.compose.foundation.gestures.snapping.SnapLayoutInfoProvider
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import androidx.compose.foundation.gestures.snapping.rememberSnapFlingBehavior
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import androidx.compose.foundation.layout.Arrangement
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import androidx.compose.foundation.layout.Box
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@@ -7,6 +10,7 @@ import androidx.compose.foundation.layout.BoxScope
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import androidx.compose.foundation.layout.PaddingValues
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import androidx.compose.foundation.layout.wrapContentSize
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import androidx.compose.foundation.lazy.LazyListItemInfo
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+import androidx.compose.foundation.lazy.LazyListLayoutInfo
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import androidx.compose.foundation.lazy.LazyListState
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import androidx.compose.foundation.lazy.LazyRow
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import androidx.compose.runtime.Composable
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@@ -14,6 +18,7 @@ import androidx.compose.runtime.LaunchedEffect
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import androidx.compose.runtime.Stable
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import androidx.compose.runtime.getValue
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import androidx.compose.runtime.mutableStateOf
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+import androidx.compose.runtime.remember
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import androidx.compose.runtime.saveable.Saver
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import androidx.compose.runtime.saveable.listSaver
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import androidx.compose.runtime.saveable.rememberSaveable
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@@ -21,7 +26,10 @@ import androidx.compose.runtime.setValue
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import androidx.compose.runtime.snapshotFlow
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import androidx.compose.ui.Alignment
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import androidx.compose.ui.Modifier
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+import androidx.compose.ui.unit.Density
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+import androidx.compose.ui.util.fastForEach
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import androidx.compose.ui.util.fastMaxBy
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+import androidx.compose.ui.util.fastSumBy
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import kotlinx.coroutines.flow.distinctUntilChanged
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@Composable
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@@ -79,7 +87,7 @@ private fun Pager(
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horizontalAlignment = horizontalAlignment,
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verticalArrangement = Arrangement.aligned(verticalAlignment),
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userScrollEnabled = userScrollEnabled,
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- flingBehavior = rememberSnapFlingBehavior(lazyListState = state.lazyListState),
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+ flingBehavior = rememberLazyListSnapFlingBehavior(lazyListState = state.lazyListState),
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) {
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items(
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count = count,
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@@ -102,7 +110,7 @@ private fun Pager(
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verticalAlignment = verticalAlignment,
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horizontalArrangement = Arrangement.aligned(horizontalAlignment),
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userScrollEnabled = userScrollEnabled,
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- flingBehavior = rememberSnapFlingBehavior(lazyListState = state.lazyListState),
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+ flingBehavior = rememberLazyListSnapFlingBehavior(lazyListState = state.lazyListState),
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) {
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items(
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count = count,
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@@ -180,3 +188,72 @@ class PagerState(
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)
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}
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}
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+
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+// https://android.googlesource.com/platform/frameworks/support/+/refs/changes/78/2160778/35/compose/foundation/foundation/src/commonMain/kotlin/androidx/compose/foundation/gestures/snapping/LazyListSnapLayoutInfoProvider.kt
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+private fun lazyListSnapLayoutInfoProvider(
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+ lazyListState: LazyListState,
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+ positionInLayout: (layoutSize: Float, itemSize: Float) -> Float = { layoutSize, itemSize ->
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+ layoutSize / 2f - itemSize / 2f
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+ },
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+) = object : SnapLayoutInfoProvider {
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+
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+ private val layoutInfo: LazyListLayoutInfo
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+ get() = lazyListState.layoutInfo
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+
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+ // Single page snapping is the default
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+ override fun Density.calculateApproachOffset(initialVelocity: Float): Float = 0f
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+
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+ override fun Density.calculateSnappingOffsetBounds(): ClosedFloatingPointRange<Float> {
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+ var lowerBoundOffset = Float.NEGATIVE_INFINITY
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+ var upperBoundOffset = Float.POSITIVE_INFINITY
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+
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+ layoutInfo.visibleItemsInfo.fastForEach { item ->
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+ val offset =
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+ calculateDistanceToDesiredSnapPosition(layoutInfo, item, positionInLayout)
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+
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+ // Find item that is closest to the center
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+ if (offset <= 0 && offset > lowerBoundOffset) {
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+ lowerBoundOffset = offset
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+ }
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+
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+ // Find item that is closest to center, but after it
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+ if (offset >= 0 && offset < upperBoundOffset) {
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+ upperBoundOffset = offset
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+ }
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+ }
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+
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+ return lowerBoundOffset.rangeTo(upperBoundOffset)
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+ }
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+
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+ override fun Density.calculateSnapStepSize(): Float = with(layoutInfo) {
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+ if (visibleItemsInfo.isNotEmpty()) {
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+ visibleItemsInfo.fastSumBy { it.size } / visibleItemsInfo.size.toFloat()
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+ } else {
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+ 0f
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+ }
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+ }
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+}
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+
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+@Composable
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+private fun rememberLazyListSnapFlingBehavior(lazyListState: LazyListState): FlingBehavior {
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+ val snappingLayout = remember(lazyListState) { lazyListSnapLayoutInfoProvider(lazyListState) }
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+ return rememberSnapFlingBehavior(snappingLayout)
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+}
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+
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+private fun calculateDistanceToDesiredSnapPosition(
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+ layoutInfo: LazyListLayoutInfo,
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+ item: LazyListItemInfo,
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+ positionInLayout: (layoutSize: Float, itemSize: Float) -> Float,
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+): Float {
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+ val containerSize =
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+ with(layoutInfo) { singleAxisViewportSize - beforeContentPadding - afterContentPadding }
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+
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+ val desiredDistance =
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+ positionInLayout(containerSize.toFloat(), item.size.toFloat())
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+
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+ val itemCurrentPosition = item.offset
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+ return itemCurrentPosition - desiredDistance
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+}
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+
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+private val LazyListLayoutInfo.singleAxisViewportSize: Int
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+ get() = if (orientation == Orientation.Vertical) viewportSize.height else viewportSize.width
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