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@@ -0,0 +1,257 @@
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+package eu.kanade.presentation.util
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+
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+/*
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+ * MIT License
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+ *
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+ * Copyright (c) 2022 Albert Chang
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+ *
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+ * Permission is hereby granted, free of charge, to any person obtaining a copy
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+ * of this software and associated documentation files (the "Software"), to deal
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+ * in the Software without restriction, including without limitation the rights
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+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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+ * copies of the Software, and to permit persons to whom the Software is
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+ * furnished to do so, subject to the following conditions:
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+ *
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+ * The above copyright notice and this permission notice shall be included in all
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+ * copies or substantial portions of the Software.
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+ *
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+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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+ * SOFTWARE.
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+ */
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+
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+/**
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+ * Code taken from https://gist.github.com/mxalbert1996/33a360fcab2105a31e5355af98216f5a
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+ * with some modifications to handle contentPadding.
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+ *
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+ * Modifiers for regular scrollable list is omitted.
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+ */
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+
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+import android.view.ViewConfiguration
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+import androidx.compose.animation.core.Animatable
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+import androidx.compose.animation.core.tween
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+import androidx.compose.foundation.gestures.Orientation
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+import androidx.compose.foundation.layout.fillMaxWidth
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+import androidx.compose.foundation.layout.padding
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+import androidx.compose.foundation.lazy.LazyColumn
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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.foundation.lazy.rememberLazyListState
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+import androidx.compose.material3.MaterialTheme
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+import androidx.compose.material3.Text
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+import androidx.compose.runtime.Composable
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+import androidx.compose.runtime.LaunchedEffect
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+import androidx.compose.runtime.remember
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+import androidx.compose.ui.Modifier
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+import androidx.compose.ui.composed
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+import androidx.compose.ui.draw.CacheDrawScope
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+import androidx.compose.ui.draw.DrawResult
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+import androidx.compose.ui.draw.drawWithCache
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+import androidx.compose.ui.geometry.Offset
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+import androidx.compose.ui.geometry.Size
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+import androidx.compose.ui.graphics.Color
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+import androidx.compose.ui.graphics.drawscope.DrawScope
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+import androidx.compose.ui.input.nestedscroll.NestedScrollConnection
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+import androidx.compose.ui.input.nestedscroll.NestedScrollSource
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+import androidx.compose.ui.input.nestedscroll.nestedScroll
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+import androidx.compose.ui.platform.LocalContext
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+import androidx.compose.ui.platform.LocalLayoutDirection
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+import androidx.compose.ui.tooling.preview.Preview
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+import androidx.compose.ui.unit.LayoutDirection
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+import androidx.compose.ui.unit.dp
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+import androidx.compose.ui.util.fastSumBy
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+import kotlinx.coroutines.channels.BufferOverflow
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+import kotlinx.coroutines.flow.MutableSharedFlow
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+import kotlinx.coroutines.flow.collectLatest
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+
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+fun Modifier.drawHorizontalScrollbar(
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+ state: LazyListState,
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+ reverseScrolling: Boolean = false,
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+ // The amount of offset the scrollbar position towards the top of the layout
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+ positionOffsetPx: Float = 0f,
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+): Modifier = drawScrollbar(state, Orientation.Horizontal, reverseScrolling, positionOffsetPx)
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+
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+fun Modifier.drawVerticalScrollbar(
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+ state: LazyListState,
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+ reverseScrolling: Boolean = false,
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+ // The amount of offset the scrollbar position towards the start of the layout
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+ positionOffsetPx: Float = 0f,
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+): Modifier = drawScrollbar(state, Orientation.Vertical, reverseScrolling, positionOffsetPx)
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+
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+private fun Modifier.drawScrollbar(
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+ state: LazyListState,
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+ orientation: Orientation,
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+ reverseScrolling: Boolean,
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+ positionOffset: Float,
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+): Modifier = drawScrollbar(
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+ orientation, reverseScrolling,
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+) { reverseDirection, atEnd, thickness, color, alpha ->
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+ val layoutInfo = state.layoutInfo
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+ val viewportSize = if (orientation == Orientation.Horizontal) {
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+ layoutInfo.viewportSize.width
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+ } else {
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+ layoutInfo.viewportSize.height
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+ } - layoutInfo.beforeContentPadding - layoutInfo.afterContentPadding
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+ val items = layoutInfo.visibleItemsInfo
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+ val itemsSize = items.fastSumBy { it.size }
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+ val showScrollbar = items.size < layoutInfo.totalItemsCount || itemsSize > viewportSize
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+ val estimatedItemSize = if (items.isEmpty()) 0f else itemsSize.toFloat() / items.size
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+ val totalSize = estimatedItemSize * layoutInfo.totalItemsCount
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+ val thumbSize = viewportSize / totalSize * viewportSize
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+ val startOffset = if (items.isEmpty()) 0f else items
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+ .first()
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+ .run {
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+ val startPadding = if (reverseDirection) layoutInfo.afterContentPadding else layoutInfo.beforeContentPadding
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+ startPadding + ((estimatedItemSize * index - offset) / totalSize * viewportSize)
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+ }
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+ val drawScrollbar = onDrawScrollbar(
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+ orientation, reverseDirection, atEnd, showScrollbar,
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+ thickness, color, alpha, thumbSize, startOffset, positionOffset,
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+ )
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+ onDrawWithContent {
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+ drawContent()
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+ drawScrollbar()
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+ }
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+}
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+
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+private fun CacheDrawScope.onDrawScrollbar(
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+ orientation: Orientation,
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+ reverseDirection: Boolean,
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+ atEnd: Boolean,
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+ showScrollbar: Boolean,
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+ thickness: Float,
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+ color: Color,
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+ alpha: () -> Float,
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+ thumbSize: Float,
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+ scrollOffset: Float,
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+ positionOffset: Float,
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+): DrawScope.() -> Unit {
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+ val topLeft = if (orientation == Orientation.Horizontal) {
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+ Offset(
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+ if (reverseDirection) size.width - scrollOffset - thumbSize else scrollOffset,
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+ if (atEnd) size.height - positionOffset - thickness else positionOffset,
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+ )
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+ } else {
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+ Offset(
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+ if (atEnd) size.width - positionOffset - thickness else positionOffset,
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+ if (reverseDirection) size.height - scrollOffset - thumbSize else scrollOffset,
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+ )
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+ }
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+ val size = if (orientation == Orientation.Horizontal) {
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+ Size(thumbSize, thickness)
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+ } else {
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+ Size(thickness, thumbSize)
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+ }
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+
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+ return {
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+ if (showScrollbar) {
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+ drawRect(
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+ color = color,
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+ topLeft = topLeft,
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+ size = size,
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+ alpha = alpha(),
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+ )
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+ }
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+ }
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+}
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+
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+private fun Modifier.drawScrollbar(
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+ orientation: Orientation,
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+ reverseScrolling: Boolean,
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+ onBuildDrawCache: CacheDrawScope.(
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+ reverseDirection: Boolean,
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+ atEnd: Boolean,
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+ thickness: Float,
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+ color: Color,
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+ alpha: () -> Float,
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+ ) -> DrawResult,
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+): Modifier = composed {
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+ val scrolled = remember {
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+ MutableSharedFlow<Unit>(
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+ extraBufferCapacity = 1,
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+ onBufferOverflow = BufferOverflow.DROP_OLDEST,
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+ )
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+ }
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+ val nestedScrollConnection = remember(orientation, scrolled) {
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+ object : NestedScrollConnection {
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+ override fun onPostScroll(
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+ consumed: Offset,
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+ available: Offset,
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+ source: NestedScrollSource,
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+ ): Offset {
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+ val delta = if (orientation == Orientation.Horizontal) consumed.x else consumed.y
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+ if (delta != 0f) scrolled.tryEmit(Unit)
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+ return Offset.Zero
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+ }
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+ }
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+ }
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+
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+ val alpha = remember { Animatable(0f) }
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+ LaunchedEffect(scrolled, alpha) {
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+ scrolled.collectLatest {
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+ alpha.snapTo(1f)
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+ alpha.animateTo(0f, animationSpec = FadeOutAnimationSpec)
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+ }
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+ }
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+
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+ val isLtr = LocalLayoutDirection.current == LayoutDirection.Ltr
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+ val reverseDirection = if (orientation == Orientation.Horizontal) {
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+ if (isLtr) reverseScrolling else !reverseScrolling
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+ } else reverseScrolling
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+ val atEnd = if (orientation == Orientation.Vertical) isLtr else true
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+
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+ val context = LocalContext.current
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+ val thickness = remember { ViewConfiguration.get(context).scaledScrollBarSize.toFloat() }
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+ val color = MaterialTheme.colorScheme.onSurface.copy(alpha = 0.364f)
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+ Modifier
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+ .nestedScroll(nestedScrollConnection)
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+ .drawWithCache {
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+ onBuildDrawCache(reverseDirection, atEnd, thickness, color, alpha::value)
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+ }
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+}
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+
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+private val FadeOutAnimationSpec = tween<Float>(
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+ durationMillis = ViewConfiguration.getScrollBarFadeDuration(),
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+ delayMillis = ViewConfiguration.getScrollDefaultDelay(),
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+)
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+
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+@Preview(widthDp = 400, heightDp = 400, showBackground = true)
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+@Composable
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+fun LazyListScrollbarPreview() {
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+ val state = rememberLazyListState()
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+ LazyColumn(
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+ modifier = Modifier.drawVerticalScrollbar(state),
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+ state = state,
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+ ) {
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+ items(50) {
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+ Text(
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+ text = "Item ${it + 1}",
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+ modifier = Modifier
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+ .fillMaxWidth()
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+ .padding(16.dp),
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+ )
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+ }
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+ }
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+}
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+
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+@Preview(widthDp = 400, showBackground = true)
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+@Composable
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+fun LazyListHorizontalScrollbarPreview() {
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+ val state = rememberLazyListState()
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+ LazyRow(
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+ modifier = Modifier.drawHorizontalScrollbar(state),
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+ state = state,
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+ ) {
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+ items(50) {
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+ Text(
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+ text = (it + 1).toString(),
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+ modifier = Modifier
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+ .padding(horizontal = 8.dp, vertical = 16.dp),
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+ )
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+ }
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+ }
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+}
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Ivan Iskandar