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Improving the reusability and maintainability in ScrollbarExt.kt file and Fix the scroll bar thumb jumping a little bit due to lack of smothness on interpolatedIndex #1550

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Improving the reusability and maintainability in ScrollbarExt.kt file and Fix the scroll bar thumb jumping a little bit due to lack of smothness on interpolatedIndex #1550

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13d4e26
Improving the reusability and maintainability in ScrollbarExt.kt file
rodrigodiasferreira Jul 14, 2024
e8d5d12
Remove the inline qualifier from the genericScrollbarState and make i…
rodrigodiasferreira Jul 14, 2024
31b77d5
Fix the scroll bar thumb jumping a little bit due to lack of smothnes…
rodrigodiasferreira Jul 15, 2024
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2 changes: 1 addition & 1 deletion ...samples/apps/nowinandroid/core/designsystem/component/scrollbar/LazyScrollbarUtilities.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,7 @@ import kotlin.math.abs
* @return a [Float] in the range [firstItemPosition..nextItemPosition) where nextItemPosition
* is the index of the consecutive item along the major axis.
* */
internal inline fun <LazyState : ScrollableState, LazyStateItem> LazyState.interpolateFirstItemIndex(
internal inline fun <LazyState : ScrollableState, LazyStateItem> LazyState.interpolateIndex(
visibleItems: List<LazyStateItem>,
crossinline itemSize: LazyState.(LazyStateItem) -> Int,
crossinline offset: LazyState.(LazyStateItem) -> Int,
Expand Down
224 changes: 96 additions & 128 deletions ...om/google/samples/apps/nowinandroid/core/designsystem/component/scrollbar/ScrollbarExt.kt
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@
package com.google.samples.apps.nowinandroid.core.designsystem.component.scrollbar

import androidx.compose.foundation.gestures.Orientation
import androidx.compose.foundation.gestures.ScrollableState
import androidx.compose.foundation.lazy.LazyListItemInfo
import androidx.compose.foundation.lazy.LazyListState
import androidx.compose.foundation.lazy.grid.LazyGridItemInfo
Expand All @@ -41,58 +42,18 @@ import kotlin.math.min
fun LazyListState.scrollbarState(
itemsAvailable: Int,
itemIndex: (LazyListItemInfo) -> Int = LazyListItemInfo::index,
): ScrollbarState {
val state = remember { ScrollbarState() }
LaunchedEffect(this, itemsAvailable) {
snapshotFlow {
if (itemsAvailable == 0) return@snapshotFlow null

val visibleItemsInfo = layoutInfo.visibleItemsInfo
if (visibleItemsInfo.isEmpty()) return@snapshotFlow null

val firstIndex = min(
a = interpolateFirstItemIndex(
visibleItems = visibleItemsInfo,
itemSize = { it.size },
offset = { it.offset },
nextItemOnMainAxis = { first -> visibleItemsInfo.find { it != first } },
itemIndex = itemIndex,
),
b = itemsAvailable.toFloat(),
)
if (firstIndex.isNaN()) return@snapshotFlow null

val itemsVisible = visibleItemsInfo.floatSumOf { itemInfo ->
itemVisibilityPercentage(
itemSize = itemInfo.size,
itemStartOffset = itemInfo.offset,
viewportStartOffset = layoutInfo.viewportStartOffset,
viewportEndOffset = layoutInfo.viewportEndOffset,
)
}

val thumbTravelPercent = min(
a = firstIndex / itemsAvailable,
b = 1f,
)
val thumbSizePercent = min(
a = itemsVisible / itemsAvailable,
b = 1f,
)
scrollbarStateValue(
thumbSizePercent = thumbSizePercent,
thumbMovedPercent = when {
layoutInfo.reverseLayout -> 1f - thumbTravelPercent
else -> thumbTravelPercent
},
)
}
.filterNotNull()
.distinctUntilChanged()
.collect { state.onScroll(it) }
}
return state
}
) = genericScrollbarState(
itemsAvailable = itemsAvailable,
visibleItems = { layoutInfo.visibleItemsInfo },
visibleItemsOnMainAxis = { layoutInfo.visibleItemsInfo },
itemSize = { it.size },
offset = { it.offset },
nextItemOnMainAxis = { first -> layoutInfo.visibleItemsInfo.find { it != first } },
index = itemIndex,
viewportStartOffset = { layoutInfo.viewportStartOffset },
viewportEndOffset = { layoutInfo.viewportEndOffset },
reverseLayout = { layoutInfo.reverseLayout },
)

/**
* Calculates a [ScrollbarState] driven by the changes in a [LazyGridState]
Expand All @@ -104,68 +65,33 @@ fun LazyListState.scrollbarState(
fun LazyGridState.scrollbarState(
itemsAvailable: Int,
itemIndex: (LazyGridItemInfo) -> Int = LazyGridItemInfo::index,
): ScrollbarState {
val state = remember { ScrollbarState() }
LaunchedEffect(this, itemsAvailable) {
snapshotFlow {
if (itemsAvailable == 0) return@snapshotFlow null

val visibleItemsInfo = layoutInfo.visibleItemsInfo
if (visibleItemsInfo.isEmpty()) return@snapshotFlow null

val firstIndex = min(
a = interpolateFirstItemIndex(
visibleItems = visibleItemsInfo,
itemSize = { layoutInfo.orientation.valueOf(it.size) },
offset = { layoutInfo.orientation.valueOf(it.offset) },
nextItemOnMainAxis = { first ->
when (layoutInfo.orientation) {
Orientation.Vertical -> visibleItemsInfo.find {
it != first && it.row != first.row
}

Orientation.Horizontal -> visibleItemsInfo.find {
it != first && it.column != first.column
}
}
},
itemIndex = itemIndex,
),
b = itemsAvailable.toFloat(),
)
if (firstIndex.isNaN()) return@snapshotFlow null

val itemsVisible = visibleItemsInfo.floatSumOf { itemInfo ->
itemVisibilityPercentage(
itemSize = layoutInfo.orientation.valueOf(itemInfo.size),
itemStartOffset = layoutInfo.orientation.valueOf(itemInfo.offset),
viewportStartOffset = layoutInfo.viewportStartOffset,
viewportEndOffset = layoutInfo.viewportEndOffset,
)
) = genericScrollbarState(
itemsAvailable = itemsAvailable,
visibleItems = { layoutInfo.visibleItemsInfo },
visibleItemsOnMainAxis = {
when (layoutInfo.orientation) {
Orientation.Vertical -> layoutInfo.visibleItemsInfo.filter { it.row == 0 }
Orientation.Horizontal -> layoutInfo.visibleItemsInfo.filter { it.column == 0 }
}
},
itemSize = { layoutInfo.orientation.valueOf(it.size) },
offset = { layoutInfo.orientation.valueOf(it.offset) },
nextItemOnMainAxis = { first ->
when (layoutInfo.orientation) {
Orientation.Vertical -> layoutInfo.visibleItemsInfo.find {
it != first && it.row != first.row
}

val thumbTravelPercent = min(
a = firstIndex / itemsAvailable,
b = 1f,
)
val thumbSizePercent = min(
a = itemsVisible / itemsAvailable,
b = 1f,
)
scrollbarStateValue(
thumbSizePercent = thumbSizePercent,
thumbMovedPercent = when {
layoutInfo.reverseLayout -> 1f - thumbTravelPercent
else -> thumbTravelPercent
},
)
Orientation.Horizontal -> layoutInfo.visibleItemsInfo.find {
it != first && it.column != first.column
}
}
.filterNotNull()
.distinctUntilChanged()
.collect { state.onScroll(it) }
}
return state
}
},
index = itemIndex,
viewportStartOffset = { layoutInfo.viewportStartOffset },
viewportEndOffset = { layoutInfo.viewportEndOffset },
reverseLayout = { layoutInfo.reverseLayout },
)

/**
* Remembers a [ScrollbarState] driven by the changes in a [LazyStaggeredGridState]
Expand All @@ -178,40 +104,79 @@ fun LazyGridState.scrollbarState(
fun LazyStaggeredGridState.scrollbarState(
itemsAvailable: Int,
itemIndex: (LazyStaggeredGridItemInfo) -> Int = LazyStaggeredGridItemInfo::index,
) = genericScrollbarState(
itemsAvailable = itemsAvailable,
visibleItems = { layoutInfo.visibleItemsInfo },
visibleItemsOnMainAxis = { layoutInfo.visibleItemsInfo.filter { it.lane == 0 } },
itemSize = { layoutInfo.orientation.valueOf(it.size) },
offset = { layoutInfo.orientation.valueOf(it.offset) },
nextItemOnMainAxis = { first ->
layoutInfo.visibleItemsInfo.find { it != first && it.lane == first.lane }
},
index = itemIndex,
viewportStartOffset = { layoutInfo.viewportStartOffset },
viewportEndOffset = { layoutInfo.viewportEndOffset },
)

/**
* Calculates a [ScrollbarState] driven by the changes in a [LazyState].
*
* @param itemsAvailable the total amount of items available to scroll in the [LazyState].
* @param itemSize a lookup function for the size of an item in the layout.
* @param offset a lookup function for the offset of an item relative to the start of the view port.
* @param nextItemOnMainAxis a lookup function for the next item on the main axis in the direction
* of the scroll.
* @param itemSize next [LazyStateItem] on the main axis of [LazyState], null if none.
* @param index a lookup function for index of an item in the layout relative to
* @param viewportStartOffset a lookup function for the start offset of the view port
* @param viewportEndOffset a lookup function for the end offset of the view port
* @param reverseLayout a lookup function for the reverseLayout of [LazyState].
*/
@Composable
private fun <LazyState : ScrollableState, LazyStateItem> LazyState.genericScrollbarState(
itemsAvailable: Int,
visibleItems: () -> List<LazyStateItem>,
visibleItemsOnMainAxis: () -> List<LazyStateItem>,
itemSize: LazyState.(LazyStateItem) -> Int,
offset: LazyState.(LazyStateItem) -> Int,
nextItemOnMainAxis: LazyState.(LazyStateItem) -> LazyStateItem?,
index: (LazyStateItem) -> Int,
viewportStartOffset: () -> Int,
viewportEndOffset: () -> Int,
reverseLayout: () -> Boolean = { false },
): ScrollbarState {
val state = remember { ScrollbarState() }
LaunchedEffect(this, itemsAvailable) {
snapshotFlow {
if (itemsAvailable == 0) return@snapshotFlow null

val visibleItemsInfo = layoutInfo.visibleItemsInfo
val visibleItemsInfo = visibleItems()
val visibleItemsOnMainAxis = visibleItemsOnMainAxis()
if (visibleItemsInfo.isEmpty()) return@snapshotFlow null

val firstIndex = min(
a = interpolateFirstItemIndex(
visibleItems = visibleItemsInfo,
itemSize = { layoutInfo.orientation.valueOf(it.size) },
offset = { layoutInfo.orientation.valueOf(it.offset) },
nextItemOnMainAxis = { first ->
visibleItemsInfo.find { it != first && it.lane == first.lane }
},
itemIndex = itemIndex,
val interpolatedIndex = min(
a = interpolateIndex(
visibleItems = visibleItemsOnMainAxis,
itemSize = itemSize,
offset = offset,
nextItemOnMainAxis = nextItemOnMainAxis,
itemIndex = index,
),
b = itemsAvailable.toFloat(),
)
if (firstIndex.isNaN()) return@snapshotFlow null
if (interpolatedIndex.isNaN()) return@snapshotFlow null

val itemsVisible = visibleItemsInfo.floatSumOf { itemInfo ->
itemVisibilityPercentage(
itemSize = layoutInfo.orientation.valueOf(itemInfo.size),
itemStartOffset = layoutInfo.orientation.valueOf(itemInfo.offset),
viewportStartOffset = layoutInfo.viewportStartOffset,
viewportEndOffset = layoutInfo.viewportEndOffset,
itemSize = itemSize(itemInfo),
itemStartOffset = offset(itemInfo),
viewportStartOffset = viewportStartOffset(),
viewportEndOffset = viewportEndOffset(),
)
}

val thumbTravelPercent = min(
a = firstIndex / itemsAvailable,
a = interpolatedIndex / itemsAvailable,
b = 1f,
)
val thumbSizePercent = min(
Expand All @@ -220,7 +185,10 @@ fun LazyStaggeredGridState.scrollbarState(
)
scrollbarStateValue(
thumbSizePercent = thumbSizePercent,
thumbMovedPercent = thumbTravelPercent,
thumbMovedPercent = when {
reverseLayout() -> 1f - thumbTravelPercent
else -> thumbTravelPercent
},
)
}
.filterNotNull()
Expand Down