On the fly look and feel updates, change zoom hotkey to ctrl+alt+wheel

src/core/src/main/java/org/apache/jmeter/gui/AbstractJMeterGuiComponent.java

@@ -184,10 +184,15 @@ protected NamePanel getNamePanel() {
      * @return a JLabel which subclasses can add to their GUI
      */
     protected Component createTitleLabel() {
-        JLabel titleLabel = new JLabel(getStaticLabel());
-        Font curFont = titleLabel.getFont();
-        titleLabel.setFont(curFont.deriveFont((float) curFont.getSize() + 4));
-        return titleLabel;
+        return new JLabel(getStaticLabel()) {
+            @Override
+            public void updateUI() {
+                super.updateUI();
+                // Setting the font in updateUI reduces UI jumps when look and feel changes
+                Font curFont = getFont();
+                setFont(curFont.deriveFont((float) curFont.getSize() + 4));
+            }
+        };
     }
 
     /**

src/core/src/main/java/org/apache/jmeter/gui/GuiPackage.java

@@ -18,6 +18,7 @@
 package org.apache.jmeter.gui;
 
 import java.awt.Component;
+import java.awt.event.ActionEvent;
 import java.awt.event.MouseEvent;
 import java.beans.Introspector;
 import java.util.ArrayList;
@@ -36,6 +37,8 @@
 import org.apache.jmeter.engine.util.ValueReplacer;
 import org.apache.jmeter.exceptions.IllegalUserActionException;
 import org.apache.jmeter.gui.UndoHistory.HistoryListener;
+import org.apache.jmeter.gui.action.ActionNames;
+import org.apache.jmeter.gui.action.ActionRouter;
 import org.apache.jmeter.gui.action.TreeNodeNamingPolicy;
 import org.apache.jmeter.gui.action.impl.DefaultTreeNodeNamingPolicy;
 import org.apache.jmeter.gui.logging.GuiLogEventBus;
@@ -648,27 +651,24 @@ public void localeChanged(LocaleChangeEvent event) {
         // will flush it away):
         updateCurrentNode();
 
-        // Forget about all GUIs we've created so far: we'll need to re-created
-        // them all!
-        guis = new HashMap<>();
-        nodesToGui = new HashMap<>();
-        testBeanGUIs = new HashMap<>();
-
-        // BeanInfo objects also contain locale-sensitive data -- flush them
-        // away:
         Introspector.flushCaches();
 
-        // Now put the current GUI in place. [This code was copied from the
-        // EditCommand action -- we can't just trigger the action because that
-        // would populate the current node with the contents of the new GUI --
-        // which is empty.]
-        MainFrame mf = getMainFrame(); // Fetch once
-        if (mf == null) { // Probably caused by unit testing on headless system
-            log.warn("Mainframe is null");
-        } else {
-            mf.setMainPanel((javax.swing.JComponent) getCurrentGui());
-            mf.setEditMenu(getTreeListener().getCurrentNode().createPopupMenu());
-        }
+        invalidateCachedUi();
+    }
+
+    public void invalidateCachedUi() {
+        // Save current edits from the GUI to tree model just in case
+        updateCurrentNode();
+
+        // Invalidate UIs
+        guis.clear();
+        nodesToGui.clear();
+        testBeanGUIs.clear();
+
+        // Call "start edit for the current tree node" action to show the UI
+        ActionRouter.getInstance().actionPerformed(
+                new ActionEvent(this, 3334, ActionNames.EDIT)
+        );
     }
 
     private String testPlanFile;

src/core/src/main/java/org/apache/jmeter/gui/MainFrame.java

@@ -232,8 +232,8 @@ public MainFrame(TreeModel treeModel, JMeterTreeListener treeListener) {
         initTopLevelDndHandler();
         setDefaultCloseOperation(DO_NOTHING_ON_CLOSE);
 
-        int ctrlShiftMask = (IS_MAC ? InputEvent.META_DOWN_MASK : InputEvent.CTRL_DOWN_MASK) |
-                InputEvent.SHIFT_DOWN_MASK;
+        int ctrlAltMask = (IS_MAC ? InputEvent.META_DOWN_MASK : InputEvent.CTRL_DOWN_MASK) |
+                InputEvent.ALT_DOWN_MASK;
 
         addMouseWheelListener(e -> {
             if (e.getWheelRotation() == 0) {
@@ -243,7 +243,8 @@ public MainFrame(TreeModel treeModel, JMeterTreeListener treeListener) {
                 // See https://github.com/JetBrains/intellij-community/blob/21c99af7c78fc82aefc4d05646389f4991b08b38/bin/idea.properties#L133-L156
                 return;
             }
-            if ((e.getModifiersEx() & ctrlShiftMask) == ctrlShiftMask) {
+            // Shift down means "horizontal scrolling" on macOS, and we need only vertical one
+            if ((e.getModifiersEx() & (ctrlAltMask | InputEvent.SHIFT_DOWN_MASK)) == ctrlAltMask) {
                 final float scale = 1.1f;
                 int rotation = e.getWheelRotation();
                 if (rotation > 0) { // DOWN

src/core/src/main/java/org/apache/jmeter/gui/action/LookAndFeelCommand.java

@@ -30,7 +30,6 @@
 import java.util.Set;
 import java.util.prefs.Preferences;
 
-import javax.swing.JOptionPane;
 import javax.swing.UIManager;
 import javax.swing.UnsupportedLookAndFeelException;
 
@@ -212,6 +211,7 @@ public static void activateLookAndFeel(String command) {
             } else {
                 UIManager.setLookAndFeel(className);
                 UIManager.put("Button.defaultButtonFollowsFocus", false);
+                LafManager.updateLaf();
             }
             PREFS.put(USER_PREFS_KEY, item.command);
         } catch (UnsupportedLookAndFeelException
@@ -230,14 +230,7 @@ public static void activateLookAndFeel(String command) {
     public void doAction(ActionEvent ev) {
         try {
             activateLookAndFeel(ev.getActionCommand());
-            JMeterUtils.refreshUI();
-            int chosenOption = JOptionPane.showConfirmDialog(GuiPackage.getInstance().getMainFrame(), JMeterUtils
-                    .getResString("laf_quit_after_change"), // $NON-NLS-1$
-                    JMeterUtils.getResString("exit"), // $NON-NLS-1$
-                    JOptionPane.YES_NO_OPTION, JOptionPane.QUESTION_MESSAGE);
-            if (chosenOption == JOptionPane.YES_OPTION) {
-                ActionRouter.getInstance().doActionNow(new ActionEvent(ev.getSource(), ev.getID(), ActionNames.RESTART));
-            }
+            GuiPackage.getInstance().invalidateCachedUi();
         } catch (IllegalArgumentException e) {
             JMeterUtils.reportErrorToUser(e.getMessage(), e);
         }

src/core/src/main/java/org/apache/jmeter/gui/util/JMeterToolBar.java

@@ -39,6 +39,8 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import com.github.weisj.darklaf.ui.button.DarkButtonUI;
+
 /**
  * The JMeter main toolbar class
  *
@@ -126,7 +128,18 @@ private static JButton makeButtonItemRes(IconToolbarBean iconBean) throws Except
         if (imageURL == null) {
             throw new Exception("No icon for: " + iconBean.getActionName());
         }
-        JButton button = new JButton(new ImageIcon(imageURL));
+        JButton button = new JButton(new ImageIcon(imageURL)) {
+            @Override
+            public void updateUI() {
+                super.updateUI();
+                // Certain LaFs might alter button configuration, so we revert it to the way we want
+                // For instance, https://github.com/weisJ/darklaf/issues/84
+                setFocusable(false);
+                setRolloverEnabled(true);
+                putClientProperty(DarkButtonUI.KEY_VARIANT, DarkButtonUI.VARIANT_SHADOW);
+                putClientProperty(DarkButtonUI.KEY_THIN, true);
+            }
+        };
         button.setToolTipText(JMeterUtils.getResString(iconBean.getI18nKey()));
         final URL imageURLPressed = JMeterUtils.class.getClassLoader().getResource(iconBean.getIconPathPressed());
         button.setPressedIcon(new ImageIcon(imageURLPressed));

src/core/src/main/java/org/apache/jmeter/util/JMeterUtils.java

@@ -18,11 +18,8 @@
 package org.apache.jmeter.util;
 
 import java.awt.Component;
-import java.awt.Dialog;
 import java.awt.Font;
-import java.awt.Frame;
 import java.awt.HeadlessException;
-import java.awt.Window;
 import java.io.BufferedReader;
 import java.io.File;
 import java.io.FileInputStream;
@@ -73,6 +70,7 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import com.github.weisj.darklaf.LafManager;
 import com.thoughtworks.xstream.XStream;
 import com.thoughtworks.xstream.security.AnyTypePermission;
 import com.thoughtworks.xstream.security.NoTypePermission;
@@ -1267,15 +1265,7 @@ public static void applyScaleOnFonts(final float scale) {
      * Refresh UI after LAF change or resizing
      */
     public static final void refreshUI() {
-        for (Window w : Window.getWindows()) {
-            SwingUtilities.updateComponentTreeUI(w);
-            if (w.isDisplayable() &&
-                (w instanceof Frame ? !((Frame)w).isResizable() :
-                w instanceof Dialog ? !((Dialog)w).isResizable() :
-                true)) {
-                w.pack();
-            }
-        }
+        LafManager.updateLaf();
     }
 
     /**

xdocs/changes.xml

@@ -83,6 +83,12 @@ are gray. It is purely a UI change, and the behavior is not altered.
 
 <p>Tree context menu is shown even in case the node selection is changed. Previously
     the popup did disappear and it was required to select a node first and only then launch popup.</p>
+
+<p>Update look and feel without restart</p>
+
+<p>Use <keycombo><keysym>CTRL</keysym><keysym>ALT</keysym><keysym>wheel</keysym></keycombo> for zooming
+    fonts. Previous shortcut was <keycombo><keysym>CTRL</keysym><keysym>SHIFT</keysym><keysym>wheel</keysym></keycombo>,
+    however, it conflicted with horizontal scrolling.</p>
 <!--
 <ch_title>Functions</ch_title>
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