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fix(LineChart): correct PointMode valueIndex and dot alignment #173

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fix(LineChart): correct PointMode valueIndex and dot alignment #173

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87e8e28
fix(LineChart): correct PointMode valueIndex with nearest data point
saadkhalidkhan Jun 6, 2026
4c0ed35
fix(LineChart): align dot x positions with line path xPositions
saadkhalidkhan Jun 6, 2026
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97 changes: 72 additions & 25 deletions compose-charts/src/commonMain/kotlin/ir/ehsannarmani/compose_charts/LineChart.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,7 @@ import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.Job
import kotlinx.coroutines.delay
import kotlinx.coroutines.launch
import kotlin.math.abs

private data class Popup(
val properties: PopupProperties,
Expand Down Expand Up @@ -277,40 +278,64 @@ fun LineChart(
val showOnPointsThreshold =
((properties.mode as? PopupProperties.Mode.PointMode)?.threshold
?: 0.dp).toPx()
val pointX = pathData.xPositions.find {
it in positionX - showOnPointsThreshold..positionX + showOnPointsThreshold
val pointIndex = if (properties.mode is PopupProperties.Mode.PointMode && !isSingleValue) {
findNearestValueIndex(
x = positionX,
pathData = pathData,
valuesCount = line.values.size,
threshold = showOnPointsThreshold
)
} else {
null
}

if (properties.mode !is PopupProperties.Mode.PointMode || pointX != null || isSingleValue) {
val relevantX =
if (properties.mode is PopupProperties.Mode.PointMode) (pointX?.toFloat()
?: 0f) else positionX
val fraction = (relevantX / size.width)
if (properties.mode !is PopupProperties.Mode.PointMode || pointIndex != null || isSingleValue) {
val relevantX = when {
isSingleValue -> 0f
pointIndex != null -> pathData.xPositions[pointIndex].toFloat()
else -> positionX
}
val fraction = relevantX / size.width

val valueIndex = if(isSingleValue){
0
}else{
calculateValueIndex(
val valueIndex = when {
isSingleValue -> 0
pointIndex != null -> pointIndex
else -> calculateValueIndex(
fraction = fraction.toDouble(),
values = line.values,
pathData = pathData
pathData = pathData,
chartWidth = size.width.toFloat()
)
}

val popupValue = if(isSingleValue){
val popupValue = if (isSingleValue) {
Value(
calculatedValue = line.values.first(),
offset = Offset(
x = 0f,
y = size.height-calculateOffset(
y = size.height - calculateOffset(
maxValue = maxValue,
minValue = minValue,
value = line.values.first().toFloat(),
total = size.toSize().height
).toFloat()
)
)
}else{
} else if (pointIndex != null && properties.mode is PopupProperties.Mode.PointMode) {
val value = line.values[pointIndex]
Value(
calculatedValue = value,
offset = Offset(
x = pathData.xPositions[pointIndex].toFloat(),
y = size.height - calculateOffset(
maxValue = computedMaxValue,
minValue = minValue,
total = size.height.toFloat(),
value = value.toFloat()
).toFloat()
)
)
} else {
getPopupValue(
points = line.values,
fraction = fraction.toDouble(),
Expand Down Expand Up @@ -559,6 +584,7 @@ fun LineChart(
pathMeasure = pathMeasure,
scope = scope,
size = size,
xPositions = pathData.xPositions,
startIndex = pathData.startIndex,
endIndex = pathData.endIndex
)
Expand Down Expand Up @@ -622,16 +648,36 @@ private fun Indicators(
}
}

private fun findNearestValueIndex(
x: Float,
pathData: PathData,
valuesCount: Int,
threshold: Float? = null,
): Int? {
if (valuesCount <= 0) return null
val lastIndex = valuesCount - 1
val nearestIndex = pathData.xPositions.indices
.filter { it <= lastIndex }
.minByOrNull { abs(pathData.xPositions[it] - x) }
?: return null
if (threshold != null && abs(pathData.xPositions[nearestIndex] - x) > threshold) {
return null
}
return nearestIndex
}

private fun calculateValueIndex(
fraction: Double,
values: List<Double>,
pathData: PathData
pathData: PathData,
chartWidth: Float,
): Int {
val xPosition = (fraction * pathData.path.getBounds().width).toFloat()
val closestXIndex = pathData.xPositions.indexOfFirst { x ->
x >= xPosition
}
return if (closestXIndex >= 0) closestXIndex else values.size - 1
if (values.size <= 1) return 0
return findNearestValueIndex(
x = (fraction * chartWidth).toFloat(),
pathData = pathData,
valuesCount = values.size
) ?: values.lastIndex
}

private fun DrawScope.drawPopup(
Expand Down Expand Up @@ -753,6 +799,7 @@ private fun DrawScope.drawDots(
pathMeasure: PathMeasure,
scope: CoroutineScope,
size: Size? = null,
xPositions: List<Double>,
startIndex: Int,
endIndex: Int,
) {
Expand All @@ -767,11 +814,11 @@ private fun DrawScope.drawDots(
properties.confirmDraw(DotProperties.Dot(value.dataIndex, valueIndex, value.value.toDouble())) &&
valueIndex in startIndex..endIndex
) {
val dotX = xPositions.getOrElse(valueIndex) {
if (dataPoints.size <= 1) 0.0 else valueIndex * _size.width.toDouble() / (dataPoints.size - 1)
}.toFloat()
val dotOffset = Offset(
x = _size.width.spaceBetween(
itemCount = dataPoints.count(),
index = valueIndex
),
x = dotX,
y = (_size.height - calculateOffset(
maxValue = maxValue.toDouble(),
minValue = minValue.toDouble(),
Expand Down