Add light theme

Follows the system by default.

core/src/main/java/com/volmit/iris/core/IrisSettings.java

@@ -266,6 +266,7 @@ public class IrisSettings {
         public boolean useServerLaunchedGuis = true;
         public boolean maximumPregenGuiFPS = false;
         public boolean colorMode = true;
+        public String theme = "auto";
     }
 
     @Data

core/src/main/java/com/volmit/iris/core/gui/GuiHost.java

@@ -73,6 +73,11 @@ public final class GuiHost {
             public void windowClosed(WindowEvent event) {
                 MANAGED_FRAMES.remove(frame);
             }
+
+            @Override
+            public void windowActivated(WindowEvent event) {
+                StudioTheme.followSystem();
+            }
         });
         installMacQuitGuard();
         return frame;

core/src/main/java/com/volmit/iris/core/gui/MapCanvas.java

@@ -66,8 +66,8 @@ final class MapCanvas extends JPanel {
     private static final Color MOB_COLOR = StudioTheme.ERROR;
     private static final Color GRID_MINOR = new Color(255, 255, 255, 18);
     private static final Color GRID_MAJOR = new Color(255, 255, 255, 38);
-    private static final Color TILE_EMPTY_A = new Color(0x232427);
-    private static final Color TILE_EMPTY_B = new Color(0x26272B);
+    private static final Color TILE_EMPTY_A = new ThemeColor(0xF0F1F3, 0x232427);
+    private static final Color TILE_EMPTY_B = new ThemeColor(0xEBECEF, 0x26272B);
     private static final int CARD_PADDING = 12;
     private static final int NOTIFICATION_MILLIS = 2_500;
     private static final double DEFAULT_BLOCKS_PER_PIXEL = 4D;
@@ -585,6 +585,13 @@ final class MapCanvas extends JPanel {
         canvas.drawImage(currentTileLayer(), 0, 0, null);
     }
 
+    // The theme changed: the cached layer holds the old theme's background.
+    @Override
+    public void updateUI() {
+        super.updateUI();
+        tileLayerStale = true;
+    }
+
     private BufferedImage currentTileLayer() {
         int width = Math.max(1, getWidth());
         int height = Math.max(1, getHeight());

core/src/main/java/com/volmit/iris/core/gui/MapWindow.java

@@ -178,6 +178,7 @@ public final class MapWindow implements MapCanvas.Listener {
         explorerControls.forEach(toolbar::add);
 
         toolbar.add(Box.createHorizontalGlue());
+        toolbar.add(StudioToolbar.themeButton());
         JComponent help = StudioToolbar.button("Shortcuts", "Show every mouse and key shortcut (/)", canvas::toggleHelp);
         mapControls.add(help);
         toolbar.add(help);

core/src/main/java/com/volmit/iris/core/gui/ObjectRenderer.java

@@ -22,6 +22,7 @@ import com.volmit.iris.core.gui.BlockModel.Face;
 import com.volmit.iris.core.gui.BlockModel.TextureMapping;
 import com.volmit.iris.core.gui.BlockTextures.BlockTexture;
 
+import java.awt.Color;
 import java.awt.image.BufferedImage;
 import java.awt.image.DataBufferInt;
 import java.util.ArrayList;
@@ -36,8 +37,7 @@ import java.util.List;
  * what is already drawn.
  */
 final class ObjectRenderer {
-    private static final int BACKGROUND = StudioTheme.EDITOR_BACKGROUND.getRGB() & 0xFFFFFF;
-    private static final int GRID_COLOR = 0x34373C;
+    private static final Color GRID = new ThemeColor(0xE3E4E8, 0x34373C);
     private static final int GRID_LINES_PER_SIDE = 25;
     private static final double GRID_REACH = 0.7D;
     private static final double GRID_BELOW_OBJECT = 0.035D;
@@ -54,6 +54,7 @@ final class ObjectRenderer {
     private final double[] depths;
     private final boolean[] showsObject;
     private final Projection projection;
+    private final int gridColor = GRID.getRGB() & 0xFFFFFF;
 
     private ObjectRenderer(ObjectMesh mesh, ObjectCamera camera, BufferedImage image, int coveredLeftWidth) {
         this.width = image.getWidth();
@@ -71,7 +72,7 @@ final class ObjectRenderer {
     static BufferedImage render(ObjectMesh mesh, ObjectCamera camera, int width, int height, int coveredLeftWidth) {
         BufferedImage image = new BufferedImage(Math.max(1, width), Math.max(1, height), BufferedImage.TYPE_INT_RGB);
         ObjectRenderer renderer = new ObjectRenderer(mesh, camera, image, Math.max(0, Math.min(width - 1, coveredLeftWidth)));
-        Arrays.fill(renderer.pixels, BACKGROUND);
+        Arrays.fill(renderer.pixels, StudioTheme.EDITOR_BACKGROUND.getRGB() & 0xFFFFFF);
         Arrays.fill(renderer.depths, Double.NEGATIVE_INFINITY);
         renderer.drawGrid(mesh.bounds());
         for (ObjectMesh.Quad quad : mesh.solidQuads()) {
@@ -131,7 +132,7 @@ final class ObjectRenderer {
             double depth = startDepth + (endDepth - startDepth) * progress;
             if (depth > depths[index]) {
                 depths[index] = depth;
-                pixels[index] = GRID_COLOR;
+                pixels[index] = gridColor;
             }
         }
     }

core/src/main/java/com/volmit/iris/core/gui/ObjectViewport.java

@@ -77,6 +77,13 @@ final class ObjectViewport extends JComponent {
         });
     }
 
+    // The theme changed, and the last frame was drawn on the old theme's background.
+    @Override
+    public void updateUI() {
+        super.updateUI();
+        requestFrame();
+    }
+
     void show(ObjectMesh nextMesh) {
         mesh = nextMesh;
         camera = ObjectCamera.START;

core/src/main/java/com/volmit/iris/core/gui/PaletteNavigator.java

@@ -57,7 +57,6 @@ final class PaletteNavigator extends JPanel {
     private static final long serialVersionUID = -6402313718430917284L;
     private static final String HERE_CARD = "here";
     private static final String OVERVIEW_CARD = "overview";
-    private static final String DETAIL_COLOR = StudioTheme.SECONDARY_TEXT_HTML;
     private static final int MESSAGE_WRAP_WIDTH_PIXELS = 190;
 
     private final Listener listener;
@@ -438,13 +437,13 @@ final class PaletteNavigator extends JPanel {
 
     private static String biomeText(BiomeEntry biome, String note) {
         String noteText = note == null ? "" : " · " + escape(note);
-        return "<html>" + escape(biome.name()) + noteText + " <font color='" + DETAIL_COLOR + "'>" + escape(biome.key())
+        return "<html>" + escape(biome.name()) + noteText + " <font color='" + StudioTheme.SECONDARY_TEXT.toHtml() + "'>" + escape(biome.key())
                 + "</font></html>";
     }
 
     private static String labeled(String title, String name, String key) {
-        return "<html><font color='" + DETAIL_COLOR + "'>" + title + "</font>&nbsp; " + escape(name)
-                + " <font color='" + DETAIL_COLOR + "'>" + escape(key) + "</font></html>";
+        return "<html><font color='" + StudioTheme.SECONDARY_TEXT.toHtml() + "'>" + title + "</font>&nbsp; " + escape(name)
+                + " <font color='" + StudioTheme.SECONDARY_TEXT.toHtml() + "'>" + escape(key) + "</font></html>";
     }
 
     private static String escape(String text) {
@@ -477,7 +476,7 @@ final class PaletteNavigator extends JPanel {
             if (detail == null) {
                 return escape(label);
             }
-            return "<html>" + escape(label) + " <font color='" + DETAIL_COLOR + "'>" + escape(detail) + "</font></html>";
+            return "<html>" + escape(label) + " <font color='" + StudioTheme.SECONDARY_TEXT.toHtml() + "'>" + escape(detail) + "</font></html>";
         }
     }
 

core/src/main/java/com/volmit/iris/core/gui/StickyFolderHeaders.java

@@ -51,7 +51,7 @@ import java.util.List;
 final class StickyFolderHeaders extends LayerUI<JScrollPane> {
     private static final long serialVersionUID = -2205474187531254372L;
     private static final int SHADOW_HEIGHT = 4;
-    private static final Color SHADOW = new Color(0, 0, 0, 90);
+    private static final Color SHADOW = new ThemeColor(new Color(0, 0, 0, 28), new Color(0, 0, 0, 90));
     private static final Color NO_SHADOW = new Color(0, 0, 0, 0);
     // The folder handle sits one indent to the left of the folder's name, as the tree draws it.
     private static final int HANDLE_NUDGE = 1;

core/src/main/java/com/volmit/iris/core/gui/StudioTheme.java

@@ -20,62 +20,64 @@ package com.volmit.iris.core.gui;
 
 import com.formdev.flatlaf.FlatDarkLaf;
 import com.formdev.flatlaf.FlatLaf;
+import com.formdev.flatlaf.FlatLightLaf;
 import com.formdev.flatlaf.util.UIScale;
 import com.volmit.iris.Iris;
+import com.volmit.iris.core.IrisSettings;
 
 import javax.swing.BorderFactory;
 import javax.swing.UIManager;
 import javax.swing.border.Border;
 import java.awt.Color;
 import java.awt.Dimension;
+import java.awt.EventQueue;
 import java.awt.Font;
+import java.util.HashMap;
+import java.util.Locale;
 import java.util.Map;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
 import java.util.concurrent.atomic.AtomicBoolean;
 
 /**
- * The colours of IntelliJ's dark "New UI", shared by FlatLaf's controls and everything the studio windows draw themselves.
+ * The colours of IntelliJ's "New UI", light and dark, shared by FlatLaf's controls and everything the studio windows
+ * draw themselves. The theme follows the system unless the user picked light or dark.
  */
 final class StudioTheme {
-    static final Color EDITOR_BACKGROUND = new Color(0x1E1F22);
-    static final Color PANEL_BACKGROUND = new Color(0x2B2D30);
-    static final Color HOVER_BACKGROUND = new Color(0x393B40);
-    static final Color INACTIVE_SELECTION = new Color(0x43454A);
-    static final Color SELECTION = new Color(0x2E436E);
-    static final Color CONTROL_BORDER = new Color(0x4E5157);
-    static final Color SEPARATOR = new Color(0x1E1F22);
-    static final Color TEXT = new Color(0xDFE1E5);
-    static final Color SECONDARY_TEXT = new Color(0x9DA0A8);
-    static final Color MUTED_TEXT = new Color(0x6F737A);
+    static final Color EDITOR_BACKGROUND = new ThemeColor(0xFFFFFF, 0x1E1F22);
+    static final Color PANEL_BACKGROUND = new ThemeColor(0xF7F8FA, 0x2B2D30);
+    static final Color HOVER_BACKGROUND = new ThemeColor(0xDFE1E5, 0x393B40);
+    static final Color INACTIVE_SELECTION = new ThemeColor(0xDFE1E5, 0x43454A);
+    static final Color SELECTION = new ThemeColor(0xD4E2FF, 0x2E436E);
+    static final Color CONTROL_BORDER = new ThemeColor(0xC9CCD6, 0x4E5157);
+    static final Color SEPARATOR = new ThemeColor(0xEBECF0, 0x1E1F22);
+    static final Color TEXT = new ThemeColor(0x000000, 0xDFE1E5);
+    static final ThemeColor SECONDARY_TEXT = new ThemeColor(0x6C707E, 0x9DA0A8);
+    static final Color MUTED_TEXT = new ThemeColor(0x818594, 0x6F737A);
     static final Color ACCENT = new Color(0x3574F0);
-    static final Color LINK = new Color(0x548AF7);
-    static final Color ERROR = new Color(0xF75464);
-    static final Color WARNING = new Color(0xF2C55C);
-    static final Color SUCCESS = new Color(0x5FB865);
-    static final Color OVERLAY_BACKGROUND = new Color(0x2B, 0x2D, 0x30, 236);
-    static final Color OVERLAY_BORDER = new Color(0x43454A);
-    static final String SECONDARY_TEXT_HTML = "#9DA0A8";
+    static final Color LINK = new ThemeColor(0x315FBD, 0x548AF7);
+    static final Color ERROR = new ThemeColor(0xDB3B4B, 0xF75464);
+    static final Color WARNING = new ThemeColor(0xC27D04, 0xF2C55C);
+    static final Color SUCCESS = new ThemeColor(0x208A3C, 0x5FB865);
+    static final Color OVERLAY_BACKGROUND = new ThemeColor(new Color(0xFF, 0xFF, 0xFF, 240), new Color(0x2B, 0x2D, 0x30, 236));
+    static final Color OVERLAY_BORDER = new ThemeColor(0xDFE1E5, 0x43454A);
     static final int OVERLAY_ARC = 10;
 
+    private static final boolean DARK_WITHOUT_SYSTEM_PREFERENCE = true;
     private static final AtomicBoolean INSTALLED = new AtomicBoolean();
+    private static final ExecutorService SYSTEM_CHECK = Executors.newSingleThreadExecutor(runnable -> {
+        Thread thread = new Thread(runnable, "Iris Theme Check");
+        thread.setDaemon(true);
+        return thread;
+    });
+    private static volatile boolean dark = DARK_WITHOUT_SYSTEM_PREFERENCE;
     private static volatile float pixelScale = 1F;
-    private static final Map<String, String> INTELLIJ_NEW_UI_DEFAULTS = Map.ofEntries(
-            Map.entry("@background", "#2B2D30"),
-            Map.entry("@foreground", "#DFE1E5"),
-            Map.entry("@accentColor", "#3574F0"),
-            Map.entry("@selectionBackground", "#2E436E"),
-            Map.entry("@selectionInactiveBackground", "#43454A"),
-            Map.entry("@disabledForeground", "#6F737A"),
-            Map.entry("Component.borderColor", "#4E5157"),
-            Map.entry("Component.focusedBorderColor", "#3574F0"),
+    private static final Map<String, String> SHARED_DEFAULTS = Map.ofEntries(
             Map.entry("Component.focusWidth", "1"),
             Map.entry("Component.innerFocusWidth", "0"),
             Map.entry("Component.arc", "8"),
             Map.entry("Button.arc", "8"),
             Map.entry("TextComponent.arc", "8"),
-            Map.entry("Button.toolbar.hoverBackground", "#393B40"),
-            Map.entry("Button.toolbar.pressedBackground", "#43454A"),
-            Map.entry("Button.toolbar.selectedBackground", "#43454A"),
-            Map.entry("ToggleButton.toolbar.selectedBackground", "#43454A"),
             Map.entry("List.selectionArc", "6"),
             Map.entry("List.selectionInsets", "0,6,0,6"),
             Map.entry("Tree.selectionArc", "6"),
@@ -85,16 +87,49 @@ final class StudioTheme {
             Map.entry("ScrollBar.thumbArc", "999"),
             Map.entry("ScrollBar.thumbInsets", "2,2,2,2"),
             Map.entry("ScrollBar.showButtons", "false"),
-            Map.entry("ScrollBar.track", "#2B2D30"),
             Map.entry("ScrollPane.border", "0,0,0,0"),
             Map.entry("SplitPane.dividerSize", "1"),
             Map.entry("SplitPaneDivider.style", "plain"),
-            Map.entry("SplitPane.background", "#1E1F22"),
-            Map.entry("Separator.foreground", "#1E1F22"),
-            Map.entry("ToolTip.background", "#393B40"),
             Map.entry("ProgressBar.arc", "999"),
             Map.entry("ProgressBar.horizontalSize", "120,4")
     );
+    private static final Map<String, String> DARK_DEFAULTS = withShared(Map.ofEntries(
+            Map.entry("@background", "#2B2D30"),
+            Map.entry("@foreground", "#DFE1E5"),
+            Map.entry("@accentColor", "#3574F0"),
+            Map.entry("@selectionBackground", "#2E436E"),
+            Map.entry("@selectionInactiveBackground", "#43454A"),
+            Map.entry("@disabledForeground", "#6F737A"),
+            Map.entry("Component.borderColor", "#4E5157"),
+            Map.entry("Component.focusedBorderColor", "#3574F0"),
+            Map.entry("Button.toolbar.hoverBackground", "#393B40"),
+            Map.entry("Button.toolbar.pressedBackground", "#43454A"),
+            Map.entry("Button.toolbar.selectedBackground", "#43454A"),
+            Map.entry("ToggleButton.toolbar.selectedBackground", "#43454A"),
+            Map.entry("ScrollBar.track", "#2B2D30"),
+            Map.entry("SplitPane.background", "#1E1F22"),
+            Map.entry("Separator.foreground", "#1E1F22"),
+            Map.entry("ToolTip.background", "#393B40")
+    ));
+    private static final Map<String, String> LIGHT_DEFAULTS = withShared(Map.ofEntries(
+            Map.entry("@background", "#F7F8FA"),
+            Map.entry("@foreground", "#000000"),
+            Map.entry("@accentColor", "#3574F0"),
+            Map.entry("@selectionBackground", "#D4E2FF"),
+            Map.entry("@selectionForeground", "#000000"),
+            Map.entry("@selectionInactiveBackground", "#DFE1E5"),
+            Map.entry("@selectionInactiveForeground", "#000000"),
+            Map.entry("@disabledForeground", "#A8ADBD"),
+            Map.entry("Component.borderColor", "#C9CCD6"),
+            Map.entry("Component.focusedBorderColor", "#3574F0"),
+            Map.entry("Button.toolbar.hoverBackground", "#DFE1E5"),
+            Map.entry("Button.toolbar.pressedBackground", "#C9CCD6"),
+            Map.entry("Button.toolbar.selectedBackground", "#DFE1E5"),
+            Map.entry("ToggleButton.toolbar.selectedBackground", "#DFE1E5"),
+            Map.entry("ScrollBar.track", "#F7F8FA"),
+            Map.entry("SplitPane.background", "#EBECF0"),
+            Map.entry("Separator.foreground", "#EBECF0")
+    ));
 
     private StudioTheme() {
     }
@@ -104,8 +139,7 @@ final class StudioTheme {
             return;
         }
         try {
-            FlatLaf.setGlobalExtraDefaults(INTELLIJ_NEW_UI_DEFAULTS);
-            FlatDarkLaf.setup();
+            applyLookAndFeel(darkFor(mode()));
             pixelScale = UIScale.getUserScaleFactor();
         } catch (Throwable error) {
             Iris.reportError(error);
@@ -113,6 +147,71 @@ final class StudioTheme {
         }
     }
 
+    static boolean isDark() {
+        return dark;
+    }
+
+    static Mode mode() {
+        return Mode.fromSetting(IrisSettings.get().getGui().getTheme());
+    }
+
+    /**
+     * Remembers the user's choice and switches every studio window to it.
+     */
+    static void choose(Mode next) {
+        IrisSettings settings = IrisSettings.get();
+        settings.getGui().setTheme(next.settingName());
+        settings.forceSave();
+        if (next == Mode.AUTO) {
+            followSystem();
+            return;
+        }
+        switchTo(next == Mode.DARK);
+    }
+
+    // Studio windows call this when they come to the front, so a change made in the system's settings shows up.
+    static void followSystem() {
+        if (!INSTALLED.get() || mode() != Mode.AUTO) {
+            return;
+        }
+        SYSTEM_CHECK.execute(() -> {
+            boolean systemDark = SystemAppearance.prefersDark().orElse(DARK_WITHOUT_SYSTEM_PREFERENCE);
+            EventQueue.invokeLater(() -> switchTo(systemDark));
+        });
+    }
+
+    private static boolean darkFor(Mode chosen) {
+        return switch (chosen) {
+            case LIGHT -> false;
+            case DARK -> true;
+            case AUTO -> SystemAppearance.prefersDark().orElse(DARK_WITHOUT_SYSTEM_PREFERENCE);
+        };
+    }
+
+    private static void switchTo(boolean nextDark) {
+        if (nextDark == dark) {
+            return;
+        }
+        applyLookAndFeel(nextDark);
+        FlatLaf.updateUI();
+    }
+
+    private static void applyLookAndFeel(boolean nextDark) {
+        dark = nextDark;
+        FlatLaf.setGlobalExtraDefaults(nextDark ? DARK_DEFAULTS : LIGHT_DEFAULTS);
+        if (nextDark) {
+            FlatDarkLaf.setup();
+        } else {
+            FlatLightLaf.setup();
+        }
+    }
+
+    private static Map<String, String> withShared(Map<String, String> themeDefaults) {
+        Map<String, String> merged = new HashMap<>(SHARED_DEFAULTS);
+        merged.putAll(themeDefaults);
+        return Map.copyOf(merged);
+    }
+
     /**
      * FlatLaf grows fonts and its own controls to the screen's DPI; every size the studio sets itself has to grow with them.
      */
@@ -160,4 +259,33 @@ final class StudioTheme {
         Font font = UIManager.getFont(key);
         return font != null ? font : new Font(Font.SANS_SERIF, fallbackStyle, fallbackSize);
     }
+
+    enum Mode {
+        AUTO("Match system"),
+        LIGHT("Light"),
+        DARK("Dark");
+
+        private final String label;
+
+        Mode(String label) {
+            this.label = label;
+        }
+
+        String label() {
+            return label;
+        }
+
+        String settingName() {
+            return name().toLowerCase(Locale.ROOT);
+        }
+
+        static Mode fromSetting(String setting) {
+            for (Mode mode : values()) {
+                if (mode.settingName().equalsIgnoreCase(setting)) {
+                    return mode;
+                }
+            }
+            return AUTO;
+        }
+    }
 }

core/src/main/java/com/volmit/iris/core/gui/StudioToolbar.java

@@ -22,10 +22,13 @@ import com.formdev.flatlaf.FlatClientProperties;
 import com.formdev.flatlaf.icons.FlatSearchIcon;
 
 import javax.swing.BorderFactory;
+import javax.swing.ButtonGroup;
 import javax.swing.JButton;
 import javax.swing.JComponent;
 import javax.swing.JLabel;
 import javax.swing.JPanel;
+import javax.swing.JPopupMenu;
+import javax.swing.JRadioButtonMenuItem;
 import javax.swing.JScrollPane;
 import javax.swing.JTextField;
 import javax.swing.JToggleButton;
@@ -63,12 +66,39 @@ final class StudioToolbar {
     }
 
     static JButton button(String text, String tooltip, Runnable action) {
+        JButton button = toolbarButton(text, tooltip);
+        button.addActionListener(event -> action.run());
+        return button;
+    }
+
+    /**
+     * Opens a menu to pick light, dark or the system's theme.
+     */
+    static JButton themeButton() {
+        JButton button = toolbarButton("Theme", "Light, dark, or whatever the system uses");
+        button.addActionListener(event -> themeMenu().show(button, 0, button.getHeight()));
+        return button;
+    }
+
+    private static JPopupMenu themeMenu() {
+        JPopupMenu menu = new JPopupMenu();
+        ButtonGroup choices = new ButtonGroup();
+        StudioTheme.Mode current = StudioTheme.mode();
+        for (StudioTheme.Mode mode : StudioTheme.Mode.values()) {
+            JRadioButtonMenuItem item = new JRadioButtonMenuItem(mode.label(), mode == current);
+            item.addActionListener(event -> StudioTheme.choose(mode));
+            choices.add(item);
+            menu.add(item);
+        }
+        return menu;
+    }
+
+    private static JButton toolbarButton(String text, String tooltip) {
         JButton button = new JButton(text);
         button.setToolTipText(tooltip);
         button.setFocusable(false);
         button.setMargin(new Insets(4, 8, 4, 8));
         button.putClientProperty(FlatClientProperties.BUTTON_TYPE, FlatClientProperties.BUTTON_TYPE_TOOLBAR_BUTTON);
-        button.addActionListener(event -> action.run());
         return button;
     }
 

core/src/main/java/com/volmit/iris/core/gui/SystemAppearance.java

@@ -0,0 +1,110 @@
+/*
+ * Iris is a World Generator for Minecraft Bukkit Servers
+ * Copyright (c) 2022 Arcane Arts (Volmit Software)
+ *
+ * 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 <https://www.gnu.org/licenses/>.
+ */
+
+package com.volmit.iris.core.gui;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
+import java.util.List;
+import java.util.Locale;
+import java.util.Optional;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Asks the operating system whether its user prefers dark or light apps, through the same settings desktop apps
+ * follow: the freedesktop portal or GNOME's setting on Linux, the apps theme on Windows, the appearance on macOS.
+ */
+final class SystemAppearance {
+    private static final long COMMAND_TIMEOUT_MILLIS = 2000L;
+    private static final String PORTAL_DARK = "uint32 1";
+    private static final String PORTAL_LIGHT = "uint32 2";
+
+    private SystemAppearance() {
+    }
+
+    /**
+     * Empty when the system has no preference or could not be asked.
+     */
+    static Optional<Boolean> prefersDark() {
+        String os = System.getProperty("os.name", "").toLowerCase(Locale.ROOT);
+        if (os.contains("win")) {
+            return windowsPrefersDark();
+        }
+        if (os.contains("mac")) {
+            return macPrefersDark();
+        }
+        return linuxPrefersDark();
+    }
+
+    private static Optional<Boolean> linuxPrefersDark() {
+        Optional<String> portal = output(List.of("gdbus", "call", "--session", "--dest", "org.freedesktop.portal.Desktop",
+                "--object-path", "/org/freedesktop/portal/desktop", "--method", "org.freedesktop.portal.Settings.ReadOne",
+                "org.freedesktop.appearance", "color-scheme"));
+        if (portal.filter(answer -> answer.contains(PORTAL_DARK)).isPresent()) {
+            return Optional.of(true);
+        }
+        if (portal.filter(answer -> answer.contains(PORTAL_LIGHT)).isPresent()) {
+            return Optional.of(false);
+        }
+        Optional<String> gnome = output(List.of("gsettings", "get", "org.gnome.desktop.interface", "color-scheme"));
+        if (gnome.filter(scheme -> scheme.contains("prefer-dark")).isPresent()) {
+            return Optional.of(true);
+        }
+        if (gnome.filter(scheme -> scheme.contains("prefer-light")).isPresent()) {
+            return Optional.of(false);
+        }
+        return output(List.of("gsettings", "get", "org.gnome.desktop.interface", "gtk-theme"))
+                .map(theme -> theme.toLowerCase(Locale.ROOT).contains("dark"));
+    }
+
+    private static Optional<Boolean> windowsPrefersDark() {
+        return output(List.of("reg", "query", "HKCU\\Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize",
+                "/v", "AppsUseLightTheme"))
+                .filter(answer -> answer.contains("AppsUseLightTheme"))
+                .map(answer -> answer.trim().endsWith("0x0"));
+    }
+
+    // The setting only exists while macOS is dark, so a failed read means light.
+    private static Optional<Boolean> macPrefersDark() {
+        return Optional.of(output(List.of("defaults", "read", "-g", "AppleInterfaceStyle"))
+                .filter(style -> style.trim().equalsIgnoreCase("dark"))
+                .isPresent());
+    }
+
+    private static Optional<String> output(List<String> command) {
+        try {
+            Process process = new ProcessBuilder(command).redirectErrorStream(true).start();
+            if (!process.waitFor(COMMAND_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS)) {
+                process.destroyForcibly();
+                return Optional.empty();
+            }
+            if (process.exitValue() != 0) {
+                return Optional.empty();
+            }
+            try (InputStream stream = process.getInputStream()) {
+                return Optional.of(new String(stream.readAllBytes(), StandardCharsets.UTF_8));
+            }
+        } catch (IOException missingCommand) {
+            return Optional.empty();
+        } catch (InterruptedException interrupted) {
+            Thread.currentThread().interrupt();
+            return Optional.empty();
+        }
+    }
+}

core/src/main/java/com/volmit/iris/core/gui/ThemeColor.java

@@ -0,0 +1,55 @@
+/*
+ * Iris is a World Generator for Minecraft Bukkit Servers
+ * Copyright (c) 2022 Arcane Arts (Volmit Software)
+ *
+ * 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 <https://www.gnu.org/licenses/>.
+ */
+
+package com.volmit.iris.core.gui;
+
+import java.awt.Color;
+
+/**
+ * A colour with a light and a dark version that always answers with the one of the current theme, like IntelliJ's
+ * JBColor. Components keep the same colour object across a theme switch and simply paint in the other version.
+ */
+final class ThemeColor extends Color {
+    private static final long serialVersionUID = 2286435620386470207L;
+    private final Color light;
+    private final Color dark;
+
+    ThemeColor(int lightRgb, int darkRgb) {
+        this(new Color(lightRgb), new Color(darkRgb));
+    }
+
+    ThemeColor(Color light, Color dark) {
+        super(dark.getRGB(), true);
+        this.light = light;
+        this.dark = dark;
+    }
+
+    // Every other colour query of Color, and Java2D's painting, go through this one.
+    @Override
+    public int getRGB() {
+        return current().getRGB();
+    }
+
+    String toHtml() {
+        return String.format("#%06X", getRGB() & 0xFFFFFF);
+    }
+
+    private Color current() {
+        return StudioTheme.isDark() ? dark : light;
+    }
+}