[WIP] Properly scale all UI elements based on Theme.scale() setting

app/src/processing/app/Base.java

@@ -247,6 +247,8 @@ public Base(String[] args) throws Exception {
         // ignore
       }
 
+      UIHelper.scaleElements((float)(Theme.getScale()) / 100.0f);
+
       // Use native popups so they don't look so crappy on osx
       JPopupMenu.setDefaultLightWeightPopupEnabled(false);
     } else {

app/src/processing/app/UIHelper.java

@@ -0,0 +1,119 @@
+package processing.app;
+
+import java.awt.Font;
+import java.lang.reflect.Field;
+import java.util.Map;
+
+import javax.swing.JButton;
+import javax.swing.JCheckBox;
+import javax.swing.JCheckBoxMenuItem;
+import javax.swing.JComboBox;
+import javax.swing.JFrame;
+import javax.swing.JLabel;
+import javax.swing.JMenu;
+import javax.swing.JMenuBar;
+import javax.swing.JRadioButton;
+import javax.swing.JRadioButtonMenuItem;
+import javax.swing.JSlider;
+import javax.swing.JSpinner;
+import javax.swing.JTabbedPane;
+import javax.swing.JTable;
+import javax.swing.JTextArea;
+import javax.swing.JTextField;
+import javax.swing.JToggleButton;
+import javax.swing.LookAndFeel;
+import javax.swing.UIManager;
+import javax.swing.plaf.FontUIResource;
+
+import processing.app.helpers.OSUtils;
+
+public class UIHelper {
+  public static void scaleElements(float scale) throws Exception {
+
+    Font menuFont = UIManager.getFont("Menu.font");
+    Font f = new Font(menuFont.getFontName(), menuFont.getStyle(), (int)((float)menuFont.getSize() * scale));
+    UIManager.put("Button.font", f);
+    UIManager.put("ToggleButton.font", f);
+    UIManager.put("RadioButton.font", f);
+    UIManager.put("CheckBox.font", f);
+    UIManager.put("ColorChooser.font", f);
+    UIManager.put("ComboBox.font", f);
+    UIManager.put("Label.font", f);
+    UIManager.put("List.font", f);
+    UIManager.put("MenuBar.font", f);
+    UIManager.put("MenuItem.font", f);
+    UIManager.put("RadioButtonMenuItem.font", f);
+    UIManager.put("CheckBoxMenuItem.font", f);
+    UIManager.put("Menu.font", f);
+    UIManager.put("PopupMenu.font", f);
+    UIManager.put("OptionPane.font", f);
+    UIManager.put("Panel.font", f);
+    UIManager.put("ProgressBar.font", f);
+    UIManager.put("ScrollPane.font", f);
+    UIManager.put("Viewport.font", f);
+    UIManager.put("TabbedPane.font", f);
+    UIManager.put("Table.font", f);
+    UIManager.put("TableHeader.font", f);
+    UIManager.put("TextField.font", f);
+    UIManager.put("PasswordField.font", f);
+    UIManager.put("TextArea.font", f);
+    UIManager.put("TextPane.font", f);
+    UIManager.put("EditorPane.font", f);
+    UIManager.put("TitledBorder.font", f);
+    UIManager.put("ToolBar.font", f);
+    UIManager.put("ToolTip.font", f);
+    UIManager.put("Tree.font", f);
+
+    // On Linux this doesn't seem to be enough :(
+    if (OSUtils.isLinux()) {
+      checkGTKLookAndFeel(scale);
+    }
+  }
+
+  // Stolen from https://stackoverflow.com/a/31345102 , helps bypassing GTK LaF endless bugs
+  private static void checkGTKLookAndFeel(float scale) throws Exception {
+    LookAndFeel look = UIManager.getLookAndFeel();
+    if (!look.getID().equals("GTK")) return;
+
+    new JFrame();
+    new JButton();
+    new JComboBox();
+    new JRadioButton();
+    new JCheckBox();
+    new JTextArea();
+    new JTextField();
+    new JTable();
+    new JToggleButton();
+    new JSpinner();
+    new JSlider();
+    new JTabbedPane();
+    new JMenu();
+    new JMenuBar();
+    new JRadioButtonMenuItem();
+    new JLabel();
+    new JCheckBoxMenuItem();
+
+    Object styleFactory;
+    Field styleFactoryField = look.getClass().getDeclaredField("styleFactory");
+    styleFactoryField.setAccessible(true);
+    styleFactory = styleFactoryField.get(look);
+
+    Field defaultFontField = styleFactory.getClass().getDeclaredField("defaultFont");
+    defaultFontField.setAccessible(true);
+    Font defaultFont = (Font) defaultFontField.get(styleFactory);
+    FontUIResource newFontUI;
+    newFontUI = new FontUIResource(defaultFont.deriveFont((float)(defaultFont.getSize() * scale)));
+    defaultFontField.set(styleFactory, newFontUI);
+
+    Field stylesCacheField = styleFactory.getClass().getDeclaredField("stylesCache");
+    stylesCacheField.setAccessible(true);
+    Object stylesCache = stylesCacheField.get(styleFactory);
+    Map stylesMap = (Map) stylesCache;
+    for (Object mo : stylesMap.values()) {
+        Field f = mo.getClass().getDeclaredField("font");
+        f.setAccessible(true);
+        Font fo = (Font)f.get(mo);
+        f.set(mo, fo.deriveFont((float)(fo.getSize() * scale)));
+    }
+  }
+}