Demos: Add a little "Mouse" demo for showing mouse button states

This was very helpful when adding support for 5-button mice! :^)

Demos/Mouse/Makefile

@@ -0,0 +1,8 @@
+OBJS = \
+    main.o
+
+PROGRAM = Mouse
+
+LIB_DEPS = GUI IPC Gfx Core
+
+include ../../Makefile.common

Demos/Mouse/main.cpp

@@ -0,0 +1,100 @@
+#include <LibGUI/Application.h>
+#include <LibGUI/BoxLayout.h>
+#include <LibGUI/Frame.h>
+#include <LibGUI/Painter.h>
+#include <LibGUI/Widget.h>
+#include <LibGUI/Window.h>
+
+static unsigned s_mouse_button_state;
+
+class MouseButtonIndicator final : public GUI::Frame {
+    C_OBJECT(MouseButtonIndicator);
+
+public:
+    virtual ~MouseButtonIndicator() {}
+
+private:
+    virtual void paint_event(GUI::PaintEvent& event) override
+    {
+        Frame::paint_event(event);
+
+        GUI::Painter painter(*this);
+        painter.add_clip_rect(event.rect());
+
+        Color background_color;
+        Color foreground_color;
+
+        if (s_mouse_button_state & m_button) {
+            background_color = Color::Black;
+            foreground_color = Color::White;
+        } else {
+            background_color = Color::White;
+            foreground_color = Color::Black;
+        }
+
+        painter.fill_rect(frame_inner_rect(), background_color);
+        painter.draw_text(frame_inner_rect(), m_name, Gfx::TextAlignment::Center, foreground_color);
+    }
+
+    void mousedown_event(GUI::MouseEvent& event) override
+    {
+        event.ignore();
+    }
+
+    void mouseup_event(GUI::MouseEvent& event) override
+    {
+        event.ignore();
+    }
+
+    MouseButtonIndicator(const String& name, GUI::MouseButton button)
+        : m_name(name)
+        , m_button(button)
+    {
+    }
+
+    String m_name;
+    GUI::MouseButton m_button;
+};
+
+class MainWidget final : public GUI::Widget {
+    C_OBJECT(MainWidget);
+
+public:
+    void mousedown_event(GUI::MouseEvent& event) override
+    {
+        s_mouse_button_state = event.buttons();
+        update();
+        Widget::mousedown_event(event);
+    }
+
+    void mouseup_event(GUI::MouseEvent& event) override
+    {
+        s_mouse_button_state = event.buttons();
+        update();
+        Widget::mouseup_event(event);
+    }
+
+private:
+    MainWidget() {}
+};
+
+int main(int argc, char** argv)
+{
+    GUI::Application app(argc, argv);
+    auto window = GUI::Window::construct();
+    window->set_title("Mouse button demo");
+
+    auto& main_widget = window->set_main_widget<MainWidget>();
+    main_widget.set_fill_with_background_color(true);
+
+    main_widget.set_layout<GUI::VerticalBoxLayout>();
+
+    main_widget.add<MouseButtonIndicator>("Left", GUI::MouseButton::Left);
+    main_widget.add<MouseButtonIndicator>("Middle", GUI::MouseButton::Middle);
+    main_widget.add<MouseButtonIndicator>("Right", GUI::MouseButton::Right);
+    main_widget.add<MouseButtonIndicator>("Back", GUI::MouseButton::Back);
+    main_widget.add<MouseButtonIndicator>("Forward", GUI::MouseButton::Forward);
+
+    window->show();
+    return app.exec();
+}

Kernel/build-root-filesystem.sh

@@ -150,6 +150,7 @@ cp ../Demos/WidgetGallery/WidgetGallery mnt/bin/WidgetGallery
 cp ../Demos/Cube/Cube mnt/bin/Cube
 cp ../Demos/Screensaver/Screensaver mnt/bin/Screensaver
 cp ../Demos/Fire/Fire mnt/bin/Fire
+cp ../Demos/Mouse/Mouse mnt/bin/Mouse
 cp ../Demos/DynamicLink/LinkDemo/LinkDemo mnt/bin/LinkDemo
 cp ../DevTools/HackStudio/HackStudio mnt/bin/HackStudio
 cp ../DevTools/VisualBuilder/VisualBuilder mnt/bin/VisualBuilder