Change lightness of annotation color if it's not readable on pie/bar (#…

…971) * Change lightness of annotation color if it's not readable on pie/bar. * Update notebook.
JetBrains · Dec 20, 2023 · 8a93611 · 8a93611
1 parent 810360e
commit 8a93611
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Showing 5 changed files with 36 additions and 12 deletions.
diff --git a/commons/src/commonMain/kotlin/org/jetbrains/letsPlot/commons/values/Colors.kt b/commons/src/commonMain/kotlin/org/jetbrains/letsPlot/commons/values/Colors.kt
@@ -193,6 +193,12 @@ object Colors {
  return (luminance(color) + .05) / (luminance(other) + .05)
  }
 
+ fun contrastRatio(color: Color, other: Color): Double {
+ val l1 = luminance(color)
+ val l2 = luminance(other)
+ return (max(l1, l2) + .05) / (min(l1, l2) + .05)
+ }
+
  fun luminance(color: Color): Double {
  return .2126 * colorLuminance(color.red) + .7152 * colorLuminance(color.green) + .0722 * colorLuminance(color.blue)
  }

diff --git a/docs/f-23f/theme_label_text.ipynb b/docs/f-23f/theme_label_text.ipynb
diff --git a/plot-base/src/commonMain/kotlin/org/jetbrains/letsPlot/core/plot/base/geom/BarGeom.kt b/plot-base/src/commonMain/kotlin/org/jetbrains/letsPlot/core/plot/base/geom/BarGeom.kt
@@ -101,7 +101,7 @@ open class BarGeom : GeomBase() {
  val labelColor = when {
  barRect.contains(textRect) -> {
  alpha = 0.0
- AnnotationsUtil.chooseColor(p.fill()!!)
+ AnnotationsUtil.chooseColor(annotations.textStyle.color, p.fill()!!)
  }
  else -> {
  alpha = 0.75

diff --git a/plot-base/src/commonMain/kotlin/org/jetbrains/letsPlot/core/plot/base/geom/PieGeom.kt b/plot-base/src/commonMain/kotlin/org/jetbrains/letsPlot/core/plot/base/geom/PieGeom.kt
@@ -438,7 +438,7 @@ class PieGeom : GeomBase(), WithWidth, WithHeight {
  )
  }
  val textColor = when (side) {
- Side.INSIDE -> AnnotationsUtil.chooseColor(sector.p.fill()!!)
+ Side.INSIDE -> AnnotationsUtil.chooseColor(annotations.textStyle.color, sector.p.fill()!!)
  else -> annotations.textStyle.color
  }
  return AnnotationLabel(

diff --git a/.../src/commonMain/kotlin/org/jetbrains/letsPlot/core/plot/base/geom/util/AnnotationsUtil.kt b/.../src/commonMain/kotlin/org/jetbrains/letsPlot/core/plot/base/geom/util/AnnotationsUtil.kt
@@ -5,6 +5,9 @@
 
 package org.jetbrains.letsPlot.core.plot.base.geom.util
 
+import org.jetbrains.letsPlot.commons.colorspace.HSL
+import org.jetbrains.letsPlot.commons.colorspace.hslFromRgb
+import org.jetbrains.letsPlot.commons.colorspace.rgbFromHsl
 import org.jetbrains.letsPlot.commons.geometry.DoubleVector
 import org.jetbrains.letsPlot.commons.values.Color
 import org.jetbrains.letsPlot.commons.values.Colors
@@ -25,9 +28,24 @@ object AnnotationsUtil {
  )
  }
 
- fun chooseColor(background: Color) = when {
- Colors.luminance(background) < 0.5 -> Color.WHITE // if fill is dark
- else -> Color.BLACK
+ private const val LIGHTER_LUMINANCE = 0.85
+ private const val DARKER_LUMINANCE = 0.15
+ // WCAG recommend a minimum contrast ratio of 4.5:1 for normal text and 3:1 for large text
+ private const val CONTRAST_RATIO = 3.0
+
+ fun chooseColor(textColor: Color, background: Color): Color {
+ val contrastRatio = Colors.contrastRatio(background, textColor)
+ if (contrastRatio >= CONTRAST_RATIO) {
+ return textColor
+ }
+ val newLightness = when {
+ Colors.luminance(background) < 0.5 -> LIGHTER_LUMINANCE
+ else -> DARKER_LUMINANCE
+ }
+ val hsl = hslFromRgb(textColor)
+ return rgbFromHsl(
+ HSL(hsl.h, hsl.s, newLightness)
+ )
  }
 
  data class TextParams(