#2496 Displays use complementary color for aliases in dark mode (#2548)

Co-authored-by: denny <dennis.sheirer@gmail.com>

src/main/java/io/github/dsheirer/channel/metadata/ChannelMetadataPanel.java

@@ -27,6 +27,7 @@ import io.github.dsheirer.controller.channel.ChannelModel;
 import io.github.dsheirer.controller.channel.ChannelProcessingManager;
 import io.github.dsheirer.eventbus.MyEventBus;
 import io.github.dsheirer.gui.playlist.channel.ViewChannelRequest;
+import io.github.dsheirer.gui.theme.ThemeManager;
 import io.github.dsheirer.icon.IconModel;
 import io.github.dsheirer.identifier.Identifier;
 import io.github.dsheirer.identifier.configuration.FrequencyConfigurationIdentifier;
@@ -246,7 +247,8 @@ public class ChannelMetadataPanel extends JPanel implements ListSelectionListene
                 {
                     label.setText(Joiner.on(", ").skipNulls().join(aliases));
                     label.setIcon(mIconModel.getIcon(aliases.get(0).getIconName(), IconModel.DEFAULT_ICON_SIZE));
-                    label.setForeground(aliases.get(0).getDisplayColor());
+                    label.setForeground(ThemeManager.getInstance().getReadableColor(aliases.get(0).getDisplayColor(),
+                        label.getBackground()));
                 }
                 else
                 {

src/main/java/io/github/dsheirer/gui/playlist/alias/AliasConfigurationEditor.java

@@ -19,15 +19,19 @@
 
 package io.github.dsheirer.gui.playlist.alias;
 
+import com.google.common.eventbus.Subscribe;
 import io.github.dsheirer.alias.Alias;
 import io.github.dsheirer.alias.AliasFactory;
 import io.github.dsheirer.alias.AliasList;
 import io.github.dsheirer.alias.AliasModel;
+import io.github.dsheirer.eventbus.MyEventBus;
 import io.github.dsheirer.gui.control.MaxLengthUnaryOperator;
 import io.github.dsheirer.gui.playlist.Editor;
 import io.github.dsheirer.gui.playlist.IAliasListRefreshListener;
+import io.github.dsheirer.gui.theme.ThemeManager;
 import io.github.dsheirer.icon.Icon;
 import io.github.dsheirer.playlist.PlaylistManager;
+import io.github.dsheirer.preference.PreferenceType;
 import io.github.dsheirer.preference.UserPreferences;
 import java.util.ArrayList;
 import java.util.List;
@@ -66,6 +70,7 @@ import javafx.scene.layout.VBox;
 import javafx.scene.paint.Color;
 import javafx.scene.shape.Rectangle;
 import javafx.util.Callback;
+import javax.swing.UIManager;
 import jiconfont.IconCode;
 import jiconfont.icons.font_awesome.FontAwesome;
 import jiconfont.javafx.IconNode;
@@ -124,6 +129,20 @@ public class AliasConfigurationEditor extends SplitPane implements IAliasListRef
         setOrientation(Orientation.VERTICAL);
         mCurrentEditor = getAliasItemEditor();
         getItems().addAll(topBox, getAliasItemEditor());
+
+        MyEventBus.getGlobalEventBus().register(this);
+    }
+
+    /**
+     * Redraws the alias color swatches after a change to the application theme.
+     */
+    @Subscribe
+    public void onPreferenceUpdated(PreferenceType preferenceType)
+    {
+        if(preferenceType == PreferenceType.APPLICATION)
+        {
+            Platform.runLater(() -> getAliasTableView().refresh());
+        }
     }
 
     /**
@@ -727,7 +746,11 @@ public class AliasConfigurationEditor extends SplitPane implements IAliasListRef
                         if(alias != null)
                         {
                             rectangle.setVisible(true);
-                            rectangle.setFill(ColorUtil.fromInteger(alias.getColor()));
+                            java.awt.Color color = alias.getDisplayColor();
+                            java.awt.Color readable = ThemeManager.getInstance().getReadableColor(color,
+                                UIManager.getColor("TextField.background"));
+                            rectangle.setFill(ColorUtil.fromInteger(readable.equals(color) ? alias.getColor() :
+                                readable.getRGB()));
                         }
                         else
                         {

src/main/java/io/github/dsheirer/gui/theme/ColorContrast.java

@@ -0,0 +1,100 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+
+package io.github.dsheirer.gui.theme;
+
+import java.awt.Color;
+
+/**
+ * Color contrast utilities based on the WCAG relative luminance and contrast ratio definitions.
+ */
+public final class ColorContrast
+{
+    /**
+     * Minimum contrast ratio to treat a color as readable.  This is the WCAG threshold for graphics and large text.
+     * The stricter 4.5 threshold for body text would also replace saturated colors like pure red that read fine on a
+     * dark background.
+     */
+    public static final double MINIMUM_CONTRAST_RATIO = 3.0;
+
+    private static final double BLEND_STEP = 0.05;
+
+    private ColorContrast()
+    {
+    }
+
+    /**
+     * Provides a color that is readable against the background.
+     * @param color that is preferred.
+     * @param background that the color is rendered against.
+     * @return the color when it has sufficient contrast, otherwise its RGB complement, adjusted toward white or black
+     * when the complement also lacks sufficient contrast (e.g. mid-gray is its own complement).
+     */
+    public static Color getReadable(Color color, Color background)
+    {
+        if(getContrastRatio(color, background) >= MINIMUM_CONTRAST_RATIO)
+        {
+            return color;
+        }
+
+        Color complement = new Color(255 - color.getRed(), 255 - color.getGreen(), 255 - color.getBlue());
+        Color target = getContrastRatio(Color.WHITE, background) >= getContrastRatio(Color.BLACK, background) ?
+            Color.WHITE : Color.BLACK;
+
+        Color readable = complement;
+
+        for(double fraction = BLEND_STEP; getContrastRatio(readable, background) < MINIMUM_CONTRAST_RATIO &&
+            fraction < 1.0; fraction += BLEND_STEP)
+        {
+            readable = blend(complement, target, fraction);
+        }
+
+        return getContrastRatio(readable, background) < MINIMUM_CONTRAST_RATIO ? target : readable;
+    }
+
+    /**
+     * Contrast ratio between two colors.
+     * @return ratio in the range 1.0 (identical luminance) to 21.0 (black and white).
+     */
+    public static double getContrastRatio(Color a, Color b)
+    {
+        double luminanceA = getRelativeLuminance(a);
+        double luminanceB = getRelativeLuminance(b);
+        return (Math.max(luminanceA, luminanceB) + 0.05) / (Math.min(luminanceA, luminanceB) + 0.05);
+    }
+
+    private static double getRelativeLuminance(Color color)
+    {
+        return 0.2126 * linearize(color.getRed()) + 0.7152 * linearize(color.getGreen()) +
+            0.0722 * linearize(color.getBlue());
+    }
+
+    private static double linearize(int value)
+    {
+        double normalized = value / 255.0;
+        return normalized <= 0.04045 ? normalized / 12.92 : Math.pow((normalized + 0.055) / 1.055, 2.4);
+    }
+
+    private static Color blend(Color from, Color to, double fraction)
+    {
+        return new Color((int)Math.round(from.getRed() + (to.getRed() - from.getRed()) * fraction),
+            (int)Math.round(from.getGreen() + (to.getGreen() - from.getGreen()) * fraction),
+            (int)Math.round(from.getBlue() + (to.getBlue() - from.getBlue()) * fraction));
+    }
+}

src/main/java/io/github/dsheirer/gui/theme/ThemeManager.java

@@ -221,6 +221,18 @@ public class ThemeManager
         return mCurrentTheme != null && mCurrentTheme.isDark();
     }
 
+    /**
+     * Provides the color to render user-selected content (e.g. an alias) against a background in the current theme.
+     * @param color selected by the user.
+     * @param background that the color is rendered against.
+     * @return the color, or a readable alternative when dark mode is active and the color lacks contrast with the
+     * background.
+     */
+    public Color getReadableColor(Color color, Color background)
+    {
+        return isDarkMode() ? ColorContrast.getReadable(color, background) : color;
+    }
+
     public void register(Scene scene)
     {
         if(scene == null)

src/main/java/io/github/dsheirer/module/decode/event/DecodeEventPanel.java

@@ -26,6 +26,7 @@ import io.github.dsheirer.alias.AliasModel;
 import io.github.dsheirer.channel.IChannelDescriptor;
 import io.github.dsheirer.eventbus.MyEventBus;
 import io.github.dsheirer.filter.FilterSet;
+import io.github.dsheirer.gui.theme.ThemeManager;
 import io.github.dsheirer.icon.IconModel;
 import io.github.dsheirer.identifier.Form;
 import io.github.dsheirer.identifier.Identifier;
@@ -285,7 +286,8 @@ public class DecodeEventPanel extends JPanel implements Listener<ProcessingChain
                                     sb.append(",");
                                 }
                                 sb.append(Joiner.on(", ").skipNulls().join(aliases));
-                                color = aliases.getFirst().getDisplayColor();
+                                color = ThemeManager.getInstance().getReadableColor(
+                                    aliases.getFirst().getDisplayColor(), label.getBackground());
                                 icon = mIconModel.getIcon(aliases.getFirst().getIconName(), IconModel.DEFAULT_ICON_SIZE);
                             }
                         }

src/test/java/io/github/dsheirer/gui/theme/ColorContrastTest.java

@@ -0,0 +1,66 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2026 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+
+package io.github.dsheirer.gui.theme;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.awt.Color;
+import org.junit.jupiter.api.Test;
+
+class ColorContrastTest
+{
+    private static final Color DARK_BACKGROUND = new Color(0x2B2B2B);
+    private static final Color SELECTION_BACKGROUND = new Color(0x214283);
+
+    @Test
+    void blackBecomesWhite()
+    {
+        assertEquals(Color.WHITE, ColorContrast.getReadable(Color.BLACK, DARK_BACKGROUND));
+    }
+
+    @Test
+    void lowContrastColorBecomesComplement()
+    {
+        assertEquals(Color.YELLOW, ColorContrast.getReadable(Color.BLUE, DARK_BACKGROUND));
+    }
+
+    @Test
+    void readableColorsAreUnchanged()
+    {
+        assertEquals(Color.RED, ColorContrast.getReadable(Color.RED, DARK_BACKGROUND));
+        assertEquals(Color.ORANGE, ColorContrast.getReadable(Color.ORANGE, DARK_BACKGROUND));
+    }
+
+    @Test
+    void everyGrayIsReadable()
+    {
+        for(int value = 0; value < 256; value++)
+        {
+            Color gray = new Color(value, value, value);
+
+            for(Color background: new Color[]{DARK_BACKGROUND, SELECTION_BACKGROUND, new Color(127, 127, 127)})
+            {
+                assertTrue(ColorContrast.getContrastRatio(ColorContrast.getReadable(gray, background), background) >=
+                    ColorContrast.MINIMUM_CONTRAST_RATIO, "Gray " + value + " on " + background);
+            }
+        }
+    }
+}