feat(bar): add per-bar colors support

androidApp/src/screenshotTest/kotlin/io/github/dautovicharis/charts/app/screenshot/BarChartScreenshotTest.kt

@@ -27,14 +27,34 @@ fun BarChartDefaultPreview() {
 @Composable
 fun BarChartCustomPreview() {
     ScreenshotSurface {
+        val dataSet = SCREENSHOT_BAR_SAMPLE_USE_CASE.initialBarDataSet()
         BarChart(
-            dataSet = SCREENSHOT_BAR_SAMPLE_USE_CASE.initialBarDataSet(),
+            dataSet = dataSet,
             style = ChartTestStyleFixtures.barCustomStyle(chartViewStyle = ChartViewDefaults.style()),
             animateOnStart = SCREENSHOT_ANIMATE_ON_START,
         )
     }
 }
 
+@PreviewTest
+@ScreenshotPreview
+@Composable
+fun BarChartCustomBarColorsPreview() {
+    ScreenshotSurface {
+        val dataSet = SCREENSHOT_BAR_SAMPLE_USE_CASE.initialBarDataSet()
+        BarChart(
+            dataSet = dataSet,
+            style =
+                ChartTestStyleFixtures.barCustomStyle(
+                    chartViewStyle = ChartViewDefaults.style(),
+                    barCount = dataSet.data.item.points.size,
+                    useBarColors = true,
+                ),
+            animateOnStart = SCREENSHOT_ANIMATE_ON_START,
+        )
+    }
+}
+
 @PreviewTest
 @ScreenshotPreview
 @Composable

app/src/commonMain/kotlin/io/github/dautovicharis/charts/app/demo/bar/BarChartStyleItems.kt

@@ -23,24 +23,29 @@ object BarChartStyleItems {
 
     @Composable
     fun customStyle(
+        barCount: Int,
         minValue: Float,
         maxValue: Float,
         aspectRatioPreset: ChartAspectRatioPreset = ChartAspectRatioPreset.Square,
     ) = ChartTestStyleFixtures.barCustomStyle(
         chartViewStyle = chartViewStyle(aspectRatioPreset),
+        barCount = barCount,
+        useBarColors = true,
         minValue = minValue,
         maxValue = maxValue,
     )
 
     @Composable
     fun custom(
+        barCount: Int,
         minValue: Float,
         maxValue: Float,
         aspectRatioPreset: ChartAspectRatioPreset = ChartAspectRatioPreset.Square,
     ): StyleItems =
         ChartStyleItems(
             currentStyle =
                 customStyle(
+                    barCount = barCount,
                     minValue = minValue,
                     maxValue = maxValue,
                     aspectRatioPreset = aspectRatioPreset,

app/src/commonMain/kotlin/io/github/dautovicharis/charts/app/demo/bar/BarDemo.kt

@@ -57,6 +57,7 @@ fun BarChartDemo(
             ChartPreset.Default -> BarChartStyleItems.default(aspectRatioPreset)
             ChartPreset.Custom ->
                 BarChartStyleItems.custom(
+                    barCount = dataSet.data.item.points.size,
                     minValue = controlsState.minValue.toFloat(),
                     maxValue = controlsState.maxValue.toFloat(),
                     aspectRatioPreset = aspectRatioPreset,
@@ -120,6 +121,7 @@ fun BarChartDemo(
                         dataSet = dataSet,
                         style =
                             BarChartStyleItems.customStyle(
+                                barCount = dataSet.data.item.points.size,
                                 minValue = controlsState.minValue.toFloat(),
                                 maxValue = controlsState.maxValue.toFloat(),
                                 aspectRatioPreset = aspectRatioPreset,

charts-bar/src/commonMain/kotlin/io/github/dautovicharis/charts/BarChart.kt

@@ -30,9 +30,10 @@ fun BarChart(
     selectedBarIndex: Int = NO_SELECTION,
 ) {
     val errors =
-        remember(dataSet) {
+        remember(dataSet, style.barColors) {
             validateBarData(
                 data = dataSet.data.item,
+                colorsSize = style.barColors.size,
             )
         }
 

charts-bar/src/commonMain/kotlin/io/github/dautovicharis/charts/internal/BarValidation.kt

@@ -1,10 +1,14 @@
 package io.github.dautovicharis.charts.internal
 
 import io.github.dautovicharis.charts.internal.ValidationErrors.MIN_REQUIRED_BAR
+import io.github.dautovicharis.charts.internal.ValidationErrors.RULE_COLORS_SIZE_MISMATCH
 import io.github.dautovicharis.charts.internal.common.model.ChartData
 
 @InternalChartsApi
-fun validateBarData(data: ChartData): List<String> {
+fun validateBarData(
+    data: ChartData,
+    colorsSize: Int = 0,
+): List<String> {
     val validationErrors = mutableListOf<String>()
     val pointsSize = data.points.size
 
@@ -15,6 +19,12 @@ fun validateBarData(data: ChartData): List<String> {
         return validationErrors
     }
 
+    if (colorsSize > 0 && colorsSize != pointsSize) {
+        val validationError =
+            RULE_COLORS_SIZE_MISMATCH.format(colorsSize, pointsSize)
+        validationErrors.add(validationError)
+    }
+
     data.points.forEachIndexed { index, value ->
         if (value.isNaN()) {
             val validationError = ValidationErrors.RULE_DATA_POINT_NOT_NUMBER.format(index)

charts-bar/src/commonMain/kotlin/io/github/dautovicharis/charts/internal/barchart/BarChart.kt

@@ -42,7 +42,11 @@ internal fun BarChart(
     selectedBarIndex: Int = NO_SELECTION,
     onValueChanged: (Int) -> Unit = {},
 ) {
-    val barColor = style.barColor.copy(alpha = style.barAlpha)
+    val baseBarColor = style.barColor.copy(alpha = style.barAlpha)
+    val sourceBarColors =
+        remember(style.barColors, style.barAlpha) {
+            style.barColors.map { color -> color.copy(alpha = style.barAlpha) }
+        }
     val isPreview = LocalInspectionMode.current
     val sourceDataSize = chartData.points.size
     BoxWithConstraints(modifier = style.modifier) {
@@ -87,6 +91,17 @@ internal fun BarChart(
             }
         var denseExpanded by rememberDenseExpandedState(isDenseModeAvailable = isDenseData)
         val compactDenseMode = isDenseData && !denseExpanded
+        val compactBarCenterIndices =
+            remember(sourceDataSize, compactDenseMode, maxFitBars) {
+                if (compactDenseMode) {
+                    compactDensityCenterIndices(
+                        sourcePointsCount = sourceDataSize,
+                        targetPoints = maxFitBars,
+                    )
+                } else {
+                    emptyList()
+                }
+            }
         val renderData =
             remember(chartData, compactDenseMode, maxFitBars) {
                 if (compactDenseMode) {
@@ -98,6 +113,17 @@ internal fun BarChart(
                     chartData
                 }
             }
+        val renderBarColors =
+            remember(sourceBarColors, compactBarCenterIndices, compactDenseMode, baseBarColor) {
+                when {
+                    sourceBarColors.isEmpty() -> emptyList()
+                    !compactDenseMode -> sourceBarColors
+                    else ->
+                        compactBarCenterIndices.map { centerIndex ->
+                            sourceBarColors.getOrElse(centerIndex) { baseBarColor }
+                        }
+                }
+            }
         val dataSize = renderData.points.size
         val hasFixedRange = style.minValue != null || style.maxValue != null
         val (fixedMin, fixedMax) =
@@ -214,7 +240,8 @@ internal fun BarChart(
                 interactionEnabled = interactionEnabled,
                 dragSelectionEnabled = !isScrollable,
                 animatedValues = animatedValues,
-                barColor = barColor,
+                barColors = renderBarColors,
+                defaultBarColor = baseBarColor,
                 fixedMin = fixedMin,
                 fixedMax = fixedMax,
                 isScrollable = isScrollable,

charts-bar/src/commonMain/kotlin/io/github/dautovicharis/charts/internal/barchart/BarChartContent.kt

@@ -40,7 +40,8 @@ internal fun BarChartContent(
     interactionEnabled: Boolean,
     dragSelectionEnabled: Boolean,
     animatedValues: List<Animatable<Float, AnimationVector1D>>,
-    barColor: Color,
+    barColors: List<Color>,
+    defaultBarColor: Color,
     fixedMin: Double,
     fixedMax: Double,
     isScrollable: Boolean,
@@ -282,7 +283,8 @@ internal fun BarChartContent(
                                 animatedValues = animatedValues,
                                 visibleRange = visibleRange,
                                 selectedIndex = selectedIndex,
-                                barColor = barColor,
+                                barColors = barColors,
+                                defaultBarColor = defaultBarColor,
                                 maxValue = fixedMax,
                                 minValue = fixedMin,
                                 barWidthPx = barWidthPx,

charts-bar/src/commonMain/kotlin/io/github/dautovicharis/charts/internal/barchart/BarChartDrawing.kt

@@ -16,7 +16,8 @@ internal fun DrawScope.drawBars(
     animatedValues: List<Animatable<Float, AnimationVector1D>>,
     visibleRange: IntRange,
     selectedIndex: Int,
-    barColor: Color,
+    barColors: List<Color>,
+    defaultBarColor: Color,
     maxValue: Double,
     minValue: Double,
     barWidthPx: Float,
@@ -70,9 +71,10 @@ internal fun DrawScope.drawBars(
         val barHeight = abs(value) * size.height
         val top = if (value >= 0f) clampedBaselineY - barHeight else clampedBaselineY
         val left = unitWidth * index
+        val resolvedBarColor = barColors.getOrNull(index) ?: defaultBarColor
 
         drawRect(
-            color = barColor,
+            color = resolvedBarColor,
             topLeft = Offset(x = left, y = top),
             size =
                 androidx.compose.ui.geometry.Size(

charts-bar/src/commonMain/kotlin/io/github/dautovicharis/charts/internal/barchart/BarChartHelpers.kt

@@ -101,6 +101,22 @@ internal fun aggregateForCompactDensity(
     return aggregatedPoints.toChartData(labels = aggregatedLabels)
 }
 
+internal fun compactDensityCenterIndices(
+    sourcePointsCount: Int,
+    targetPoints: Int = BAR_DENSE_THRESHOLD,
+): List<Int> {
+    if (sourcePointsCount <= 0) return emptyList()
+    if (targetPoints <= 1 || sourcePointsCount <= targetPoints) {
+        return List(sourcePointsCount) { index -> index }
+    }
+
+    val bucketSize = bucketSizeForTargetCore(totalPoints = sourcePointsCount, targetPoints = targetPoints)
+    val bucketRanges = buildBucketRangesCore(totalPoints = sourcePointsCount, bucketSize = bucketSize)
+    return bucketRanges.map { range ->
+        range.first + ((range.last - range.first) / 2)
+    }
+}
+
 internal fun maxBarsThatFit(
     viewportWidthPx: Float,
     spacingPx: Float,

charts-bar/src/commonMain/kotlin/io/github/dautovicharis/charts/style/BarChartStyle.kt

@@ -16,6 +16,7 @@ import androidx.compose.ui.unit.sp
  * @property modifier The modifier to be applied to the chart.
  * @property chartViewStyle The style to be applied to the chart view.
  * @property barColor The color to be used for the bars in the chart.
+ * @property barColors Optional explicit colors used for individual bars.
  * @property barAlpha The alpha value applied to rendered bars.
  * @property space The space between the bars in the chart.
  * @property minValue Optional fixed minimum value for the chart scale.
@@ -46,6 +47,7 @@ class BarChartStyle(
     val modifier: Modifier,
     val chartViewStyle: ChartViewStyle,
     val barColor: Color,
+    val barColors: List<Color>,
     val barAlpha: Float,
     val space: Dp,
     val minValue: Float?,
@@ -77,6 +79,7 @@ class BarChartStyle(
     override fun getProperties(): List<Pair<String, Any>> =
         listOf(
             BarChartStyle::barColor.name to barColor,
+            BarChartStyle::barColors.name to barColors,
             BarChartStyle::barAlpha.name to barAlpha,
             BarChartStyle::space.name to space,
             BarChartStyle::minValue.name to (minValue ?: "auto"),
@@ -127,6 +130,7 @@ object BarChartDefaults {
      * Returns a BarChartStyle with the provided parameters or their default values.
      *
      * @param barColor The color to be used for the bars in the chart. Defaults to the primary color of the MaterialTheme.
+     * @param barColors Optional explicit colors used for individual bars. Defaults to an empty list.
      * @param barAlpha The alpha value applied to rendered bars. Defaults to 0.4f in light theme and 0.6f in dark theme.
      * @param space The space between the bars in the chart. Defaults to 10.dp.
      * @param minValue Optional fixed minimum value for the chart scale. Defaults to null.
@@ -156,6 +160,7 @@ object BarChartDefaults {
     @Composable
     fun style(
         barColor: Color = MaterialTheme.colorScheme.primary,
+        barColors: List<Color> = emptyList(),
         barAlpha: Float = defaultChartAlpha(),
         space: Dp = 10.dp,
         minValue: Float? = null,
@@ -187,6 +192,7 @@ object BarChartDefaults {
         return BarChartStyle(
             modifier = modifier,
             barColor = barColor,
+            barColors = barColors,
             barAlpha = barAlpha.coerceIn(0f, 1f),
             space = space,
             minValue = minValue,

charts-bar/src/commonTest/kotlin/io/github/dautovicharis/charts/ui/BarChartTest.kt

@@ -1,5 +1,6 @@
 package io.github.dautovicharis.charts.ui
 
+import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.test.ExperimentalTestApi
 import androidx.compose.ui.test.assertTextEquals
 import androidx.compose.ui.test.isDisplayed
@@ -9,13 +10,15 @@ import androidx.compose.ui.test.runComposeUiTest
 import io.github.dautovicharis.charts.BarChart
 import io.github.dautovicharis.charts.internal.TestTags
 import io.github.dautovicharis.charts.internal.ValidationErrors.MIN_REQUIRED_BAR
+import io.github.dautovicharis.charts.internal.ValidationErrors.RULE_COLORS_SIZE_MISMATCH
 import io.github.dautovicharis.charts.internal.ValidationErrors.RULE_DATA_POINTS_LESS_THAN_MIN
 import io.github.dautovicharis.charts.internal.common.model.ChartDataType
 import io.github.dautovicharis.charts.internal.format
 import io.github.dautovicharis.charts.mock.MockTest.TITLE
 import io.github.dautovicharis.charts.mock.MockTest.dataSet
 import io.github.dautovicharis.charts.model.ChartDataSet
 import io.github.dautovicharis.charts.model.toChartDataSet
+import io.github.dautovicharis.charts.style.BarChartDefaults
 import kotlin.test.Test
 import kotlin.test.assertTrue
 
@@ -104,4 +107,47 @@ class BarChartTest {
 
             assertTrue(lastLabelBounds.right <= axisBounds.right - 1f)
         }
+
+    @OptIn(ExperimentalTestApi::class)
+    @Test
+    fun barChart_withMatchingBarColors_displaysChart() =
+        runComposeUiTest {
+            setContent {
+                val style =
+                    BarChartDefaults.style(
+                        barColors = listOf(Color.Red, Color.Green, Color.Blue, Color.Cyan),
+                    )
+                BarChart(
+                    dataSet = dataSet,
+                    style = style,
+                )
+            }
+
+            onNodeWithTag(TestTags.BAR_CHART).isDisplayed()
+        }
+
+    @OptIn(ExperimentalTestApi::class)
+    @Test
+    fun barChart_withInvalidBarColors_displaysError() =
+        runComposeUiTest {
+            val expectedError =
+                RULE_COLORS_SIZE_MISMATCH.format(
+                    2,
+                    dataSet.data.item.points.size,
+                )
+
+            setContent {
+                val style =
+                    BarChartDefaults.style(
+                        barColors = listOf(Color.Red, Color.Green),
+                    )
+                BarChart(
+                    dataSet = dataSet,
+                    style = style,
+                )
+            }
+
+            onNodeWithTag(TestTags.CHART_ERROR).isDisplayed()
+            onNodeWithText("${expectedError}\n").isDisplayed()
+        }
 }