Add basic z-order for Windows.

Widgets/Window.h

@@ -4,11 +4,12 @@
 #include "Rect.h"
 #include "GraphicsBitmap.h"
 #include <AK/AKString.h>
+#include <AK/InlineLinkedList.h>
 #include <AK/WeakPtr.h>
 
 class Widget;
 
-class Window final : public Object {
+class Window final : public Object, public InlineLinkedListNode<Window> {
 public:
     explicit Window(Object* parent = nullptr);
     virtual ~Window() override;
@@ -55,6 +56,11 @@ public:
 
     void did_paint();
 
+    // For InlineLinkedList.
+    // FIXME: Maybe make a ListHashSet and then WindowManager can just use that.
+    Window* m_next { nullptr };
+    Window* m_prev { nullptr };
+
 private:
     String m_title;
     Rect m_rect;

Widgets/WindowManager.cpp

@@ -60,7 +60,7 @@ WindowManager::~WindowManager()
 
 void WindowManager::paintWindowFrames()
 {
-    for (auto* window : m_windows)
+    for (auto* window = m_windows_in_order.head(); window; window = window->next())
         paintWindowFrame(*window);
 }
 
@@ -123,20 +123,27 @@ void WindowManager::paintWindowFrame(Window& window)
 void WindowManager::addWindow(Window& window)
 {
     m_windows.set(&window);
+    m_windows_in_order.append(&window);
     if (!activeWindow())
         setActiveWindow(&window);
 }
 
+void WindowManager::move_to_front(Window& window)
+{
+    m_windows_in_order.remove(&window);
+    m_windows_in_order.append(&window);
+}
+
 void WindowManager::repaint()
 {
     handlePaintEvent(*make<PaintEvent>());
 }
 
-void WindowManager::did_paint(Window& window)
+void WindowManager::did_paint(Window&)
 {
     auto& framebuffer = FrameBufferSDL::the();
     framebuffer.blit({ 0, 0 }, *m_rootWidget->backing());
-    for (auto* window : m_windows) {
+    for (auto* window = m_windows_in_order.head(); window; window = window->next()) {
         ASSERT(window->backing());
         framebuffer.blit(window->position(), *window->backing());
     }
@@ -149,6 +156,7 @@ void WindowManager::removeWindow(Window& window)
         return;
 
     m_windows.remove(&window);
+    m_windows_in_order.remove(&window);
     if (!activeWindow() && !m_windows.is_empty())
         setActiveWindow(*m_windows.begin());
 
@@ -200,7 +208,7 @@ void WindowManager::repaintAfterMove(const Rect& oldRect, const Rect& newRect)
 
     m_rootWidget->repaint(oldRect);
     m_rootWidget->repaint(newRect);
-    for (auto* window : m_windows) {
+    for (auto* window = m_windows_in_order.head(); window; window = window->next()) {
         if (outerRectForWindow(*window).intersects(oldRect) || outerRectForWindow(*window).intersects(newRect)) {
             paintWindowFrame(*window);
             window->repaint();
@@ -233,18 +241,21 @@ void WindowManager::processMouseEvent(MouseEvent& event)
         }
     }
 
-    // FIXME: Respect z-order of windows...
+    for (auto* window = m_windows_in_order.head(); window; window = window->next()) {
-    for (auto* window : m_windows) {
         if (titleBarRectForWindow(*window).contains(event.position())) {
-            if (event.type() == Event::MouseDown)
+            if (event.type() == Event::MouseDown) {
+                move_to_front(*window);
                 setActiveWindow(window);
+            }
             handleTitleBarMouseEvent(*window, event);
             return;
         }
 
         if (window->rect().contains(event.position())) {
-            if (event.type() == Event::MouseDown)
+            if (event.type() == Event::MouseDown) {
+                move_to_front(*window);
                 setActiveWindow(window);
+            }
             // FIXME: Re-use the existing event instead of crafting a new one?
             auto localEvent = make<MouseEvent>(event.type(), event.x() - window->rect().x(), event.y() - window->rect().y(), event.button());
             window->event(*localEvent);
@@ -264,12 +275,12 @@ void WindowManager::handlePaintEvent(PaintEvent& event)
     m_rootWidget->event(event);
     paintWindowFrames();
 
-    for (auto* window : m_windows)
+    for (auto* window = m_windows_in_order.head(); window; window = window->next())
         window->event(event);
 
     auto& framebuffer = FrameBufferSDL::the();
     framebuffer.blit({ 0, 0 }, *m_rootWidget->backing());
-    for (auto* window : m_windows) {
+    for (auto* window = m_windows_in_order.head(); window; window = window->next()) {
         ASSERT(window->backing());
         framebuffer.blit(window->position(), *window->backing());
     }

Widgets/WindowManager.h

@@ -4,6 +4,7 @@
 #include "Rect.h"
 #include "Color.h"
 #include <AK/HashTable.h>
+#include <AK/InlineLinkedList.h>
 #include <AK/WeakPtr.h>
 
 class MouseEvent;
@@ -32,6 +33,7 @@ public:
     void did_paint(Window&);
 
     void repaint();
+    void move_to_front(Window&);
 
 private:
     WindowManager();
@@ -52,6 +54,7 @@ private:
 
     void paintWindowFrame(Window&);
     HashTable<Window*> m_windows;
+    InlineLinkedList<Window> m_windows_in_order;
     Widget* m_rootWidget { nullptr };
 
     WeakPtr<Window> m_activeWindow;