From 8e1b5b4803b0da76f0ed5091d3fb1b6c3b2359f5 Mon Sep 17 00:00:00 2001
From: Ivan Iskandar <12537387+ivaniskandar@users.noreply.github.com>
Date: Tue, 20 Dec 2022 21:16:43 +0700
Subject: [PATCH] Pager: Bring back previous snapping behavior (#8776)
New default LazyList snap behavior is optimized for non-pager use.
---
.../kanade/presentation/components/Pager.kt | 81 ++++++++++++++++++-
1 file changed, 79 insertions(+), 2 deletions(-)
diff --git a/app/src/main/java/eu/kanade/presentation/components/Pager.kt b/app/src/main/java/eu/kanade/presentation/components/Pager.kt
index 285abac68..9e21256e3 100644
--- a/app/src/main/java/eu/kanade/presentation/components/Pager.kt
+++ b/app/src/main/java/eu/kanade/presentation/components/Pager.kt
@@ -1,5 +1,8 @@
package eu.kanade.presentation.components
+import androidx.compose.foundation.gestures.FlingBehavior
+import androidx.compose.foundation.gestures.Orientation
+import androidx.compose.foundation.gestures.snapping.SnapLayoutInfoProvider
import androidx.compose.foundation.gestures.snapping.rememberSnapFlingBehavior
import androidx.compose.foundation.layout.Arrangement
import androidx.compose.foundation.layout.Box
@@ -7,6 +10,7 @@ import androidx.compose.foundation.layout.BoxScope
import androidx.compose.foundation.layout.PaddingValues
import androidx.compose.foundation.layout.wrapContentSize
import androidx.compose.foundation.lazy.LazyListItemInfo
+import androidx.compose.foundation.lazy.LazyListLayoutInfo
import androidx.compose.foundation.lazy.LazyListState
import androidx.compose.foundation.lazy.LazyRow
import androidx.compose.runtime.Composable
@@ -14,6 +18,7 @@ import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.Stable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
import androidx.compose.runtime.saveable.Saver
import androidx.compose.runtime.saveable.listSaver
import androidx.compose.runtime.saveable.rememberSaveable
@@ -21,7 +26,10 @@ import androidx.compose.runtime.setValue
import androidx.compose.runtime.snapshotFlow
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
+import androidx.compose.ui.unit.Density
+import androidx.compose.ui.util.fastForEach
import androidx.compose.ui.util.fastMaxBy
+import androidx.compose.ui.util.fastSumBy
import kotlinx.coroutines.flow.distinctUntilChanged
@Composable
@@ -79,7 +87,7 @@ private fun Pager(
horizontalAlignment = horizontalAlignment,
verticalArrangement = Arrangement.aligned(verticalAlignment),
userScrollEnabled = userScrollEnabled,
- flingBehavior = rememberSnapFlingBehavior(lazyListState = state.lazyListState),
+ flingBehavior = rememberLazyListSnapFlingBehavior(lazyListState = state.lazyListState),
) {
items(
count = count,
@@ -102,7 +110,7 @@ private fun Pager(
verticalAlignment = verticalAlignment,
horizontalArrangement = Arrangement.aligned(horizontalAlignment),
userScrollEnabled = userScrollEnabled,
- flingBehavior = rememberSnapFlingBehavior(lazyListState = state.lazyListState),
+ flingBehavior = rememberLazyListSnapFlingBehavior(lazyListState = state.lazyListState),
) {
items(
count = count,
@@ -180,3 +188,72 @@ class PagerState(
)
}
}
+
+// 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
+private fun lazyListSnapLayoutInfoProvider(
+ lazyListState: LazyListState,
+ positionInLayout: (layoutSize: Float, itemSize: Float) -> Float = { layoutSize, itemSize ->
+ layoutSize / 2f - itemSize / 2f
+ },
+) = object : SnapLayoutInfoProvider {
+
+ private val layoutInfo: LazyListLayoutInfo
+ get() = lazyListState.layoutInfo
+
+ // Single page snapping is the default
+ override fun Density.calculateApproachOffset(initialVelocity: Float): Float = 0f
+
+ override fun Density.calculateSnappingOffsetBounds(): ClosedFloatingPointRange<Float> {
+ var lowerBoundOffset = Float.NEGATIVE_INFINITY
+ var upperBoundOffset = Float.POSITIVE_INFINITY
+
+ layoutInfo.visibleItemsInfo.fastForEach { item ->
+ val offset =
+ calculateDistanceToDesiredSnapPosition(layoutInfo, item, positionInLayout)
+
+ // Find item that is closest to the center
+ if (offset <= 0 && offset > lowerBoundOffset) {
+ lowerBoundOffset = offset
+ }
+
+ // Find item that is closest to center, but after it
+ if (offset >= 0 && offset < upperBoundOffset) {
+ upperBoundOffset = offset
+ }
+ }
+
+ return lowerBoundOffset.rangeTo(upperBoundOffset)
+ }
+
+ override fun Density.calculateSnapStepSize(): Float = with(layoutInfo) {
+ if (visibleItemsInfo.isNotEmpty()) {
+ visibleItemsInfo.fastSumBy { it.size } / visibleItemsInfo.size.toFloat()
+ } else {
+ 0f
+ }
+ }
+}
+
+@Composable
+private fun rememberLazyListSnapFlingBehavior(lazyListState: LazyListState): FlingBehavior {
+ val snappingLayout = remember(lazyListState) { lazyListSnapLayoutInfoProvider(lazyListState) }
+ return rememberSnapFlingBehavior(snappingLayout)
+}
+
+private fun calculateDistanceToDesiredSnapPosition(
+ layoutInfo: LazyListLayoutInfo,
+ item: LazyListItemInfo,
+ positionInLayout: (layoutSize: Float, itemSize: Float) -> Float,
+): Float {
+ val containerSize =
+ with(layoutInfo) { singleAxisViewportSize - beforeContentPadding - afterContentPadding }
+
+ val desiredDistance =
+ positionInLayout(containerSize.toFloat(), item.size.toFloat())
+
+ val itemCurrentPosition = item.offset
+ return itemCurrentPosition - desiredDistance
+}
+
+private val LazyListLayoutInfo.singleAxisViewportSize: Int
+ get() = if (orientation == Orientation.Vertical) viewportSize.height else viewportSize.width