Added option to center tabs in JTabbedPane.

core/src/main/java/com/github/weisj/darklaf/ui/tabbedpane/DarkHandler.java

@@ -154,6 +154,9 @@ public class DarkHandler extends TabbedPaneHandler {
                 ui.westComp = null;
             }
             ui.tabPane.doLayout();
+        } else if (DarkTabbedPaneUI.KEY_CENTER_TABS.endsWith(key)) {
+            ui.tabPane.doLayout();
+            ui.tabPane.repaint();
         }
     }
 

core/src/main/java/com/github/weisj/darklaf/ui/tabbedpane/DarkTabbedPaneLayout.java

@@ -35,6 +35,24 @@ public class DarkTabbedPaneLayout extends TabbedPaneLayout {
         this.ui = ui;
     }
 
+
+    @Override
+    protected void centerTabs(final int tabPlacement, final int tabCount, final int returnAt) {
+        if (ui.runCount == 1 && Boolean.TRUE.equals(ui.tabPane.getClientProperty(DarkTabbedPaneUI.KEY_CENTER_TABS))) {
+            if (ui.isHorizontalTabPlacement()) {
+                int shift = (returnAt - (ui.rects[tabCount - 1].x + ui.rects[tabCount - 1].width)) / 2;
+                for (int i = 0; i < tabCount; i++) {
+                    ui.rects[i].x += shift;
+                }
+            } else {
+                int shift = (returnAt - (ui.rects[tabCount - 1].y + ui.rects[tabCount - 1].height)) / 2;
+                for (int i = 0; i < tabCount; i++) {
+                    ui.rects[i].y += shift;
+                }
+            }
+        }
+    }
+
     /*
      * Non scroll-layout
      */

core/src/main/java/com/github/weisj/darklaf/ui/tabbedpane/DarkTabbedPaneScrollLayout.java

@@ -325,6 +325,12 @@ public class DarkTabbedPaneScrollLayout extends TabbedPaneScrollLayout {
                 shiftBoundsToVisibleX(selectedBounds, leftMargin, returnAt, tabCount);
             }
             restoreHiddenTabsX(leftMargin, returnAt, tabCount);
+
+            if (ui.minVisible == 0 && ui.maxVisible == tabCount - 1
+                && Boolean.TRUE.equals(ui.tabPane.getClientProperty(DarkTabbedPaneUI.KEY_CENTER_TABS))) {
+                adjustForCenterX(leftMargin, returnAt, tabCount);
+            }
+
             if (tabsButton.isVisible() && ui.tabPane.getSelectedIndex() < ui.maxVisible) {
                 //Shift again. Hiding the the tab button might reveal the last tab.
                 //Only do this if the last visible tab is not currently selected.
@@ -339,6 +345,7 @@ public class DarkTabbedPaneScrollLayout extends TabbedPaneScrollLayout {
             adjustForDropX(leftMargin, returnAt, tabCount);
 
             layoutMoreTabsButton(tabCount);
+
             commitShiftX(ui.currentShiftXTmp, tabCount);
             ui.currentShiftX = ui.currentShiftXTmp;
 
@@ -371,6 +378,12 @@ public class DarkTabbedPaneScrollLayout extends TabbedPaneScrollLayout {
                 shiftBoundsToVisibleY(selectedBounds, topMargin, returnAt, tabCount);
             }
             restoreHiddenTabsY(topMargin, returnAt, tabCount);
+
+            if (ui.minVisible == 0 && ui.maxVisible == tabCount - 1
+                && Boolean.TRUE.equals(ui.tabPane.getClientProperty(DarkTabbedPaneUI.KEY_CENTER_TABS))) {
+                adjustForCenterY(topMargin, returnAt, tabCount);
+            }
+
             if (tabsButton.isVisible() && ui.tabPane.getSelectedIndex() < ui.maxVisible) {
                 shiftTabsY(0, topMargin, bottomMargin, tabCount, false);
                 if (ui.minVisible > 0 || ui.maxVisible < tabCount - 1) {
@@ -390,6 +403,20 @@ public class DarkTabbedPaneScrollLayout extends TabbedPaneScrollLayout {
         ui.tabScroller.tabPanel.setPreferredSize(tabBounds.getSize());
     }
 
+    @Override
+    protected void centerTabs(final int tabPlacement, final int tabCount, final int returnAt) {
+        // Do nothing.
+    }
+
+    protected void adjustForCenterX(final int leftMargin, final int returnAt, final int tabCount) {
+        int shift = (returnAt - (ui.rects[tabCount - 1].x + ui.rects[tabCount - 1].width)) / 2;
+        shiftTabsX(shift, 0, returnAt, tabCount - 1, true);
+    }
+
+    protected void adjustForCenterY(final int topMargin, final int returnAt, final int tabCount) {
+        int shift = (returnAt - (ui.rects[tabCount - 1].y + ui.rects[tabCount - 1].height)) / 2;
+        shiftTabsY(shift, 0, returnAt, tabCount - 1, true);
+    }
 
     @Override
     protected int preferredTabAreaWidth(final int tabPlacement, final int height) {

core/src/main/java/com/github/weisj/darklaf/ui/tabbedpane/DarkTabbedPaneUI.java

@@ -46,6 +46,12 @@ import java.util.function.Consumer;
 public class DarkTabbedPaneUI extends DarkTabbedPaneUIBridge {
 
     protected static final String KEY_PREFIX = "JTabbedPane.";
+    /*
+     * Centering tabs only applies if in
+     *  - WRAP_TAB_LAYOUT there is only one tab run.
+     *  - SCROLL_TAB_LAYOUT the viewport doesn't need to be scrolled.
+     */
+    public static final String KEY_CENTER_TABS = KEY_PREFIX + "centerTabs";
     public static final String KEY_DND = KEY_PREFIX + "dndEnabled";
     public static final String KEY_NORTH_COMP = KEY_PREFIX + "northComponent";
     public static final String KEY_WEST_COMP = KEY_PREFIX + "westComponent";

core/src/main/java/com/github/weisj/darklaf/ui/tabbedpane/TabbedPaneLayout.java

@@ -30,7 +30,7 @@ import java.awt.*;
  * This class should be treated as a "protected" inner class. Instantiate it only within subclasses of
  * BasicTabbedPaneUI.
  */
-public class TabbedPaneLayout implements LayoutManager {
+public abstract class TabbedPaneLayout implements LayoutManager {
 
     protected final DarkTabbedPaneUIBridge ui;
 
@@ -395,6 +395,7 @@ public class TabbedPaneLayout implements LayoutManager {
             }
         }
 
+        centerTabs(tabPlacement, tabCount, returnAt);
         // Pad the selected tab so that it appears raised in front
         padSelectedTab(tabPlacement, selectedIndex);
 
@@ -409,6 +410,8 @@ public class TabbedPaneLayout implements LayoutManager {
         }
     }
 
+    protected abstract void centerTabs(final int tabPlacement, final int tabCount, int returnAt);
+
     /**
      * Normalizes the tab runs.
      *

core/src/main/java/com/github/weisj/darklaf/ui/tabbedpane/TabbedPaneScrollLayout.java

@@ -23,9 +23,6 @@
  */
 package com.github.weisj.darklaf.ui.tabbedpane;
 
-import javax.swing.*;
-import java.awt.*;
-
 abstract class TabbedPaneScrollLayout extends TabbedPaneLayout {
 
 
@@ -33,103 +30,7 @@ abstract class TabbedPaneScrollLayout extends TabbedPaneLayout {
         super(ui);
     }
 
-    protected void calculateTabRects(final int tabPlacement, final int tabCount) {
+    protected abstract void calculateTabRects(final int tabPlacement, final int tabCount);
-        FontMetrics metrics = ui.getFontMetrics();
-        Dimension size = ui.tabPane.getSize();
-        Insets insets = ui.tabPane.getInsets();
-        Insets tabAreaInsets = ui.getTabAreaInsets(tabPlacement);
-        int fontHeight = metrics.getHeight();
-        int selectedIndex = ui.tabPane.getSelectedIndex();
-        int i;
-        boolean verticalTabRuns = (tabPlacement == SwingConstants.LEFT || tabPlacement == SwingConstants.RIGHT);
-        boolean leftToRight = ui.tabPane.getComponentOrientation().isLeftToRight();
-        int x = tabAreaInsets.left;
-        int y = tabAreaInsets.top;
-        int totalWidth = 0;
-        int totalHeight = 0;
-
-        //
-        // Calculate bounds within which a tab run must fit
-        //
-        switch (tabPlacement) {
-            case SwingConstants.LEFT:
-            case SwingConstants.RIGHT:
-                ui.maxTabWidth = ui.calculateMaxTabWidth(tabPlacement);
-                break;
-            case SwingConstants.BOTTOM:
-            case SwingConstants.TOP:
-            default:
-                ui.maxTabHeight = ui.calculateMaxTabHeight(tabPlacement);
-        }
-
-        ui.runCount = 0;
-        ui.selectedRun = -1;
-
-        if (tabCount == 0) {
-            return;
-        }
-
-        ui.selectedRun = 0;
-        ui.runCount = 1;
-
-        // Run through tabs and lay them out in a single run
-        Rectangle rect;
-        for (i = 0; i < tabCount; i++) {
-            rect = ui.rects[i];
-
-            if (!verticalTabRuns) {
-                // Tabs on TOP or BOTTOM....
-                if (i > 0) {
-                    rect.x = ui.rects[i - 1].x + ui.rects[i - 1].width;
-                } else {
-                    ui.tabRuns[0] = 0;
-                    ui.maxTabWidth = 0;
-                    totalHeight += ui.maxTabHeight;
-                    rect.x = x;
-                }
-                rect.width = ui.calculateTabWidth(tabPlacement, i, metrics);
-                totalWidth = rect.x + rect.width;
-                ui.maxTabWidth = Math.max(ui.maxTabWidth, rect.width);
-
-                rect.y = y;
-                rect.height = ui.maxTabHeight/* - 2*/;
-
-            } else {
-                // Tabs on LEFT or RIGHT...
-                if (i > 0) {
-                    rect.y = ui.rects[i - 1].y + ui.rects[i - 1].height;
-                } else {
-                    ui.tabRuns[0] = 0;
-                    ui.maxTabHeight = 0;
-                    totalWidth = ui.maxTabWidth;
-                    rect.y = y;
-                }
-                rect.height = ui.calculateTabHeight(tabPlacement, i, fontHeight);
-                totalHeight = rect.y + rect.height;
-                ui.maxTabHeight = Math.max(ui.maxTabHeight, rect.height);
-
-                rect.x = x;
-                rect.width = ui.maxTabWidth/* - 2*/;
-
-            }
-        }
-
-        if (ui.tabsOverlapBorder) {
-            // Pad the selected tab so that it appears raised in front
-            padSelectedTab(tabPlacement, selectedIndex);
-        }
-
-        // if right to left and tab placement on the top or
-        // the bottom, flip x positions and adjust by widths
-        if (!leftToRight && !verticalTabRuns) {
-            int rightMargin = size.width
-                              - (insets.right + tabAreaInsets.right);
-            for (i = 0; i < tabCount; i++) {
-                ui.rects[i].x = rightMargin - ui.rects[i].x - ui.rects[i].width;
-            }
-        }
-        ui.tabScroller.tabPanel.setPreferredSize(new Dimension(totalWidth, totalHeight));
-    }
 
     protected int preferredTabAreaWidth(final int tabPlacement, final int height) {
         return ui.calculateMaxTabWidth(tabPlacement);