Preliminary support for custom decorations.

src/main/java/com/weis/darklaf/ui/rootpane/DarkTitlePane.java

@@ -217,8 +217,8 @@ public class DarkTitlePane extends JComponent {
         titleLabel = new JLabel();
         add(titleLabel);
         if (decorationStyle == JRootPane.FRAME) {
-            createActions();
             createIcons();
+            createActions();
             createButtons();
 
             windowIconButton = createWindowIcon();
@@ -294,13 +294,21 @@ public class DarkTitlePane extends JComponent {
     }
 
     private void addMenuItems(@NotNull final JPopupMenu menu) {
-        menu.add(restoreAction);
-        menu.add(minimizeAction);
+        menu.add(new JMenuItem(restoreAction) {{
+            setDisabledIcon(restoreIcon);
+        }});
+        menu.add(new JMenuItem(minimizeAction) {{
+            setDisabledIcon(minimizeIcon);
+        }});
         if (Toolkit.getDefaultToolkit().isFrameStateSupported(Frame.MAXIMIZED_BOTH)) {
-            menu.add(maximizeAction);
+            menu.add(new JMenuItem(maximizeAction) {{
+                setDisabledIcon(maximizeIcon);
+            }});
         }
         menu.add(new JSeparator());
-        menu.add(closeAction);
+        menu.add(new JMenuItem(closeAction) {{
+            setDisabledIcon(closeIcon);
+        }});
     }
 
     private void close() {
@@ -362,8 +370,6 @@ public class DarkTitlePane extends JComponent {
     private void createButtons() {
         closeButton = createButton("Close", closeIcon, closeAction);
         closeButton.setRolloverIcon(UIManager.getIcon("TitlePane.closeHover.icon"));
-        closeButton.putClientProperty("rolloverColor", Color.RED);
-        closeButton.putClientProperty("rolloverArmedColor", Color.RED);
         closeButton.setUI(new CloseButtonUI());
 
         if (getWindowDecorationStyle() == JRootPane.FRAME) {
@@ -524,7 +530,7 @@ public class DarkTitlePane extends JComponent {
 
     private class CloseAction extends AbstractAction {
         public CloseAction() {
-            super("Close");
+            super("Close", closeIcon);
         }
 
         public void actionPerformed(final ActionEvent e) {
@@ -536,7 +542,7 @@ public class DarkTitlePane extends JComponent {
     private class MinimizeAction extends AbstractAction {
         public MinimizeAction() {
             //UIManager.getString("Minimize", getLocale())
-            super("Minimize");
+            super("Minimize", minimizeIcon);
         }
 
         public void actionPerformed(final ActionEvent e) {
@@ -546,7 +552,7 @@ public class DarkTitlePane extends JComponent {
 
     private class MaximizeAction extends AbstractAction {
         public MaximizeAction() {
-            super("Maximize");
+            super("Maximize", maximizeIcon);
         }
 
         public void actionPerformed(final ActionEvent e) {
@@ -556,7 +562,7 @@ public class DarkTitlePane extends JComponent {
 
     private class RestoreAction extends AbstractAction {
         public RestoreAction() {
-            super("Restore");
+            super("Restore", restoreIcon);
         }
 
         public void actionPerformed(final ActionEvent e) {

src/main/java/com/weis/darklaf/util/WindowsFrameUtil.java

@@ -0,0 +1,79 @@
+package com.weis.darklaf.util;
+
+import com.sun.jna.LastErrorException;
+import com.sun.jna.Native;
+import com.sun.jna.Pointer;
+import com.sun.jna.platform.win32.User32;
+import com.sun.jna.platform.win32.WinDef;
+import com.sun.jna.platform.win32.WinDef.HWND;
+import com.sun.jna.win32.StdCallLibrary;
+import com.sun.jna.win32.W32APIOptions;
+import org.jetbrains.annotations.Contract;
+import org.jetbrains.annotations.NotNull;
+
+import java.awt.*;
+
+public final class WindowsFrameUtil {
+
+    public static final WinDef.LRESULT PASS_TO_SUPER = new WinDef.LRESULT(-1);
+    public static final WinDef.LRESULT PASS_TO_DEFAULT = new WinDef.LRESULT(-2);
+    private static int prevWndProc;
+
+    public static void enableTitleBar(final Window window, final boolean enabled) {
+        if (window == null) return;
+
+        final HWND hwnd = getHWND(window);
+        int style = User32.INSTANCE.GetWindowLong(hwnd, User32dll.GWL_STYLE);
+        if (enabled) {
+            style |= 0xc00000;
+        } else {
+            style = 0x00040000;
+        }
+        //ResizeMode="CanResizeWithGrip" AllowsTransparency="True"
+        User32.INSTANCE.SetWindowLong(hwnd, User32dll.GWL_STYLE, style);
+        User32.INSTANCE.SetWindowPos(hwnd, new HWND(new Pointer(0L)),
+                                     0, 0, 0, 0, 0x27);
+    }
+
+    public static void setWindowCallback(final Window window, final WindowProc callback) {
+        if (window == null) return;
+
+        final HWND hwnd = getHWND(window);
+        callback.parent = User32dll.INSTANCE.GetWindowLongPtr(hwnd, (long) User32dll.GWL_WNDPROC);
+        User32dll.INSTANCE.SetWindowLongPtr(hwnd, User32dll.GWL_WNDPROC, callback);
+    }
+
+    @NotNull
+    @Contract("_ -> new")
+    public static HWND getHWND(final Component component) {
+        var hwnd = new HWND();
+        hwnd.setPointer(Native.getComponentPointer(component));
+        return hwnd;
+    }
+
+    public interface User32dll extends User32 {
+
+        User32dll INSTANCE = Native.loadLibrary("user32", User32dll.class,
+                                                W32APIOptions.UNICODE_OPTIONS);
+
+        WNDPROC GetWindowLongPtr(HWND hWnd, long nIndex) throws LastErrorException;
+
+        LONG_PTR SetWindowLongPtr(HWND hWnd, int nIndex, WNDPROC wndProc) throws LastErrorException;
+
+        void DisableProcessWindowsGhosting() throws LastErrorException;
+
+        INT_PTR GetWindowDC(HWND hwnd);
+
+        int ReleaseDC(HWND hwnd, INT_PTR hdc);
+    }
+
+    public interface WNDPROC extends StdCallLibrary.StdCallCallback {
+        WinDef.LRESULT callback(HWND hWnd, int uMsg, WinDef.WPARAM uParam, WinDef.LPARAM lParam) throws LastErrorException;
+    }
+
+    public abstract static class WindowProc implements WNDPROC {
+
+        protected WNDPROC parent;
+
+    }
+}