Get rid of the "root widget" concept in WindowManager.

Instead just create a GraphicsBitmap wrapper around the display framebuffer
and teach Painter how to draw directly into a GraphicsBitmap.

Kernel/Makefile

@@ -55,7 +55,6 @@ WIDGETS_OBJS = \
     ../Widgets/Color.o \
     ../Widgets/CharacterBitmap.o \
     ../Widgets/EventLoop.o \
-    ../Widgets/RootWidget.o \
     ../Widgets/Label.o \
     ../Widgets/Button.o \
     ../Widgets/MsgBox.o \

Kernel/WindowComposer.cpp

@@ -3,7 +3,6 @@
 #include <Widgets/Font.h>
 #include <Widgets/FrameBuffer.h>
 #include <Widgets/WindowManager.h>
-#include <Widgets/RootWidget.h>
 #include <Widgets/EventLoop.h>
 #include <Widgets/MsgBox.h>
 #include <Widgets/TextBox.h>
@@ -26,11 +25,8 @@ void WindowComposer_main()
     dbgprintf("Screen is %ux%ux%ubpp\n", info.width, info.height, info.bpp);
 
     FrameBuffer framebuffer((dword*)info.framebuffer, info.width, info.height);
-    RootWidget rw;
     EventLoop loop;
 
-    WindowManager::the().setRootWidget(&rw);
-
     MsgBox(nullptr, "Serenity Operating System");
 
     {

Widgets/Makefile

@@ -13,7 +13,6 @@ VFS_OBJS = \
     Rect.o \
     Object.o \
     Widget.o \
-    RootWidget.o \
     Color.o \
     Painter.o \
     Label.o \

Widgets/Painter.cpp

@@ -6,9 +6,15 @@
 #include <AK/Assertions.h>
 #include <AK/StdLibExtras.h>
 
+Painter::Painter(GraphicsBitmap& bitmap)
+{
+    m_font = &Font::defaultFont();
+    m_target = &bitmap;
+    m_clipRect = { { 0, 0 }, bitmap.size() };
+}
+
 Painter::Painter(Widget& widget)
-    : m_widget(widget)
-    , m_font(&widget.font())
+    : m_font(&widget.font())
 {
     m_target = widget.backing();
     ASSERT(m_target);
@@ -102,7 +108,6 @@ void Painter::drawText(const Rect& rect, const String& text, TextAlignment align
     if (alignment == TextAlignment::TopLeft) {
         point = rect.location();
     } else if (alignment == TextAlignment::CenterLeft) {
-        int textWidth = text.length() * font().glyphWidth();
         point = { rect.x(), rect.center().y() - (font().glyphHeight() / 2) };
     } else if (alignment == TextAlignment::Center) {
         int textWidth = text.length() * font().glyphWidth();

Widgets/Painter.h

@@ -16,6 +16,7 @@ class Painter {
 public:
     enum class TextAlignment { TopLeft, CenterLeft, Center };
     explicit Painter(Widget&);
+    explicit Painter(GraphicsBitmap&);
     ~Painter();
     void fillRect(const Rect&, Color);
     void drawRect(const Rect&, Color);
@@ -37,7 +38,6 @@ public:
 private:
     void set_pixel_with_draw_op(dword& pixel, const Color&);
 
-    Widget& m_widget;
     const Font* m_font;
     Point m_translation;
     Rect m_clipRect;

Widgets/RootWidget.cpp

@@ -1,29 +0,0 @@
-#include "AbstractScreen.h"
-#include "GraphicsBitmap.h"
-#include "RootWidget.h"
-#include "Painter.h"
-#include "WindowManager.h"
-#include "FrameBuffer.h"
-
-RootWidget::RootWidget()
-{
-    setWindowRelativeRect(FrameBuffer::the().rect());
-    m_backing = GraphicsBitmap::create_wrapper(size(), FrameBuffer::the().scanline(0));
-}
-
-RootWidget::~RootWidget()
-{
-}
-
-void RootWidget::paintEvent(PaintEvent& event)
-{
-    Painter painter(*this);
-    painter.fillRect(event.rect(), Color(0, 72, 96));
-}
-
-void RootWidget::mouseMoveEvent(MouseEvent& event)
-{
-    //printf("RootWidget::mouseMoveEvent: x=%d, y=%d\n", event.x(), event.y());
-    Widget::mouseMoveEvent(event);
-}
-

Widgets/RootWidget.h

@@ -1,19 +0,0 @@
-#pragma once
-
-#include "Widget.h"
-
-class GraphicsBitmap;
-
-class RootWidget final : public Widget {
-public:
-    RootWidget();
-    virtual ~RootWidget() override;
-
-private:
-    virtual void paintEvent(PaintEvent&) override;
-    virtual void mouseMoveEvent(MouseEvent&) override;
-
-    virtual GraphicsBitmap* backing() override { return m_backing.ptr(); }
-
-    RetainPtr<GraphicsBitmap> m_backing;
-};

Widgets/WindowManager.cpp

@@ -63,6 +63,8 @@ void WindowManager::initialize()
 
 WindowManager::WindowManager()
 {
+    m_root_bitmap = GraphicsBitmap::create_wrapper(FrameBuffer::the().rect().size(), FrameBuffer::the().scanline(0));
+
     m_activeWindowBorderColor = Color(0, 64, 192);
     m_activeWindowTitleColor = Color::White;
 
@@ -78,7 +80,7 @@ WindowManager::~WindowManager()
 
 void WindowManager::paintWindowFrame(Window& window)
 {
-    Painter p(*m_rootWidget);
+    Painter p(*m_root_bitmap);
 
     //printf("[WM] paintWindowFrame {%p}, rect: %d,%d %dx%d\n", &window, window.rect().x(), window.rect().y(), window.rect().width(), window.rect().height());
 
@@ -253,12 +255,12 @@ void WindowManager::compose()
         return false;
     };
     {
+        Painter p(*m_root_bitmap);
         for (auto& r : m_invalidated_rects) {
             if (any_window_contains_rect(r))
                 continue;
             dbgprintf("Repaint root %d,%d %dx%d\n", r.x(), r.y(), r.width(), r.height());
-            PaintEvent event(r);
-            m_rootWidget->paintEvent(event);
+            p.fillRect(r, Color(0, 72, 96));
         }
     }
     auto& framebuffer = FrameBuffer::the();
@@ -279,7 +281,7 @@ void WindowManager::compose()
 void WindowManager::redraw_cursor()
 {
     auto cursor_location = AbstractScreen::the().cursor_location();
-    Painter painter(*m_rootWidget);
+    Painter painter(*m_root_bitmap);
     painter.set_draw_op(Painter::DrawOp::Xor);
     auto draw_cross = [&painter] (const Point& p) {
         painter.drawLine({ p.x() - 10, p.y() }, { p.x() + 10, p.y() }, Color::Red);
@@ -307,16 +309,6 @@ void WindowManager::event(Event& event)
     return Object::event(event);
 }
 
-void WindowManager::setRootWidget(Widget* widget)
-{
-    // FIXME: Should we support switching root widgets?
-    ASSERT(!m_rootWidget);
-    ASSERT(widget);
-
-    m_rootWidget = widget;
-    EventLoop::main().postEvent(m_rootWidget, make<ShowEvent>());
-}
-
 void WindowManager::setActiveWindow(Window* window)
 {
     if (window == m_activeWindow.ptr())

Widgets/WindowManager.h

@@ -11,6 +11,7 @@ class MouseEvent;
 class PaintEvent;
 class Widget;
 class Window;
+class GraphicsBitmap;
 
 class WindowManager : public Object {
 public:
@@ -21,9 +22,6 @@ public:
     void notifyTitleChanged(Window&);
     void notifyRectChanged(Window&, const Rect& oldRect, const Rect& newRect);
 
-    Widget* rootWidget() { return m_rootWidget; }
-    void setRootWidget(Widget*);
-
     Window* activeWindow() { return m_activeWindow.ptr(); }
     void setActiveWindow(Window*);
 
@@ -60,7 +58,6 @@ private:
     void paintWindowFrame(Window&);
     HashTable<Window*> m_windows;
     InlineLinkedList<Window> m_windows_in_order;
-    Widget* m_rootWidget { nullptr };
 
     WeakPtr<Window> m_activeWindow;
 
@@ -76,5 +73,7 @@ private:
 
     unsigned m_recompose_count { 0 };
 
+    RetainPtr<GraphicsBitmap> m_root_bitmap;
+
     Vector<Rect> m_invalidated_rects;
 };

Widgets/test.cpp

@@ -1,6 +1,5 @@
 #include "FrameBuffer.h"
 #include "EventLoop.h"
-#include "RootWidget.h"
 #include "Label.h"
 #include "Button.h"
 #include "WindowManager.h"
@@ -19,9 +18,6 @@ int main(int argc, char** argv)
 
     EventLoop loop;
 
-    RootWidget w;
-    WindowManager::the().setRootWidget(&w);
-
     auto* fontTestWindow = new Window;
     fontTestWindow->setTitle("Font test");
     fontTestWindow->setRect({ 140, 100, 300, 80 });