LibDraw+LibGUI: Allow changing individual colors in a Palette

Palette is now a value wrapper around a NonnullRefPtr<PaletteImpl>.
A new function, set_color(ColorRole, Color) implements a simple
copy-on-write mechanism so that we're sharing the PaletteImpl in the
common case, but allowing you to create custom palettes if you like,
by getting a GWidget's palette, modifying it, and then assigning the
modified palette to the widget via GWidget::set_palette().

Use this to make PaintBrush show its palette colors once again.

Fixes #943.

Libraries/LibDraw/Palette.cpp

@@ -1,26 +1,46 @@
 #include <LibDraw/Palette.h>
 
-NonnullRefPtr<Palette> Palette::create_with_shared_buffer(SharedBuffer& buffer)
+NonnullRefPtr<PaletteImpl> PaletteImpl::create_with_shared_buffer(SharedBuffer& buffer)
 {
-    return adopt(*new Palette(buffer));
+    return adopt(*new PaletteImpl(buffer));
 }
 
-Palette::Palette(SharedBuffer& buffer)
+PaletteImpl::PaletteImpl(SharedBuffer& buffer)
     : m_theme_buffer(buffer)
 {
 }
 
+Palette::Palette(const PaletteImpl& impl)
+    : m_impl(impl)
+{
+}
+
 Palette::~Palette()
 {
 }
 
-const SystemTheme& Palette::theme() const
+const SystemTheme& PaletteImpl::theme() const
 {
     return *(const SystemTheme*)m_theme_buffer->data();
 }
 
-Color Palette::color(ColorRole role) const
+Color PaletteImpl::color(ColorRole role) const
 {
     ASSERT((int)role < (int)ColorRole::__Count);
     return theme().color[(int)role];
 }
+
+NonnullRefPtr<PaletteImpl> PaletteImpl::clone() const
+{
+    auto new_theme_buffer = SharedBuffer::create_with_size(m_theme_buffer->size());
+    memcpy(new_theme_buffer->data(), m_theme_buffer->data(), m_theme_buffer->size());
+    return adopt(*new PaletteImpl(*new_theme_buffer));
+}
+
+void Palette::set_color(ColorRole role, Color color)
+{
+    if (m_impl->ref_count() != 1)
+        m_impl = m_impl->clone();
+    auto& theme = const_cast<SystemTheme&>(impl().theme());
+    theme.color[(int)role] = color;
+}

Libraries/LibDraw/Palette.h

@@ -1,13 +1,33 @@
 #pragma once
 
 #include <AK/Badge.h>
+#include <AK/Noncopyable.h>
 #include <LibDraw/SystemTheme.h>
 
 class GApplication;
 
-class Palette : public RefCounted<Palette> {
+class PaletteImpl : public RefCounted<PaletteImpl> {
+    AK_MAKE_NONCOPYABLE(PaletteImpl)
+    AK_MAKE_NONMOVABLE(PaletteImpl)
 public:
-    static NonnullRefPtr<Palette> create_with_shared_buffer(SharedBuffer&);
+    static NonnullRefPtr<PaletteImpl> create_with_shared_buffer(SharedBuffer&);
+    NonnullRefPtr<PaletteImpl> clone() const;
+
+    Color color(ColorRole) const;
+    const SystemTheme& theme() const;
+
+    void replace_internal_buffer(Badge<GApplication>, SharedBuffer& buffer) { m_theme_buffer = buffer; }
+
+private:
+    explicit PaletteImpl(SharedBuffer&);
+
+    RefPtr<SharedBuffer> m_theme_buffer;
+};
+
+class Palette {
+
+public:
+    explicit Palette(const PaletteImpl&);
     ~Palette();
 
     Color window() const { return color(ColorRole::Window); }
@@ -41,14 +61,14 @@ public:
     Color threed_shadow2() const { return color(ColorRole::ThreedShadow2); }
     Color hover_highlight() const { return color(ColorRole::ThreedHighlight); }
 
-    Color color(ColorRole) const;
+    Color color(ColorRole role) const { return m_impl->color(role); }
+    void set_color(ColorRole, Color);
 
-    const SystemTheme& theme() const;
+    const SystemTheme& theme() const { return m_impl->theme(); }
 
-    void replace_internal_buffer(Badge<GApplication>, SharedBuffer& buffer) { m_theme_buffer = buffer; }
+    PaletteImpl& impl() { return *m_impl; }
+    const PaletteImpl& impl() const { return *m_impl; }
 
 private:
-    explicit Palette(SharedBuffer&);
-
-    RefPtr<SharedBuffer> m_theme_buffer;
+    NonnullRefPtr<PaletteImpl> m_impl;
 };

Libraries/LibDraw/SystemTheme.h

@@ -39,6 +39,7 @@ enum class ColorRole {
 
     __Count,
 
+    Background = Window,
     DisabledText = ThreedShadow1,
 };
 

Libraries/LibGUI/GApplication.cpp

@@ -147,7 +147,7 @@ void GApplication::did_delete_last_window(Badge<GWindow>)
 void GApplication::set_system_palette(SharedBuffer& buffer)
 {
     if (!m_system_palette)
-        m_system_palette = Palette::create_with_shared_buffer(buffer);
+        m_system_palette = PaletteImpl::create_with_shared_buffer(buffer);
     else
         m_system_palette->replace_internal_buffer({}, buffer);
 
@@ -157,5 +157,5 @@ void GApplication::set_system_palette(SharedBuffer& buffer)
 
 void GApplication::set_palette(const Palette& palette)
 {
-    m_palette = palette;
+    m_palette = palette.impl();
 }

Libraries/LibGUI/GApplication.h

@@ -3,6 +3,7 @@
 #include <AK/Badge.h>
 #include <AK/HashMap.h>
 #include <AK/OwnPtr.h>
+#include <LibDraw/Palette.h>
 #include <LibGUI/GShortcut.h>
 
 class CEventLoop;
@@ -42,7 +43,7 @@ public:
     const String& invoked_as() const { return m_invoked_as; }
     const Vector<String>& args() const { return m_args; }
 
-    const Palette& palette() const { return *m_palette; }
+    Palette palette() const { return Palette(*m_palette); }
     void set_palette(const Palette&);
 
     void set_system_palette(SharedBuffer&);
@@ -50,8 +51,8 @@ public:
 private:
     OwnPtr<CEventLoop> m_event_loop;
     OwnPtr<GMenuBar> m_menubar;
-    RefPtr<Palette> m_palette;
-    RefPtr<Palette> m_system_palette;
+    RefPtr<PaletteImpl> m_palette;
+    RefPtr<PaletteImpl> m_system_palette;
     HashMap<GShortcut, GAction*> m_global_shortcut_actions;
     class TooltipWindow;
     TooltipWindow* m_tooltip_window { nullptr };

Libraries/LibGUI/GWidget.cpp

@@ -67,7 +67,7 @@ const GWidgetClassRegistration* GWidgetClassRegistration::find(const String& cla
 GWidget::GWidget(GWidget* parent)
     : CObject(parent, true)
     , m_font(Font::default_font())
-    , m_palette(GApplication::the().palette())
+    , m_palette(GApplication::the().palette().impl())
 {
 }
 
@@ -695,5 +695,5 @@ Vector<GWidget*> GWidget::child_widgets() const
 
 void GWidget::set_palette(const Palette& palette)
 {
-    m_palette = palette;
+    m_palette = palette.impl();
 }

Libraries/LibGUI/GWidget.h

@@ -8,6 +8,7 @@
 #include <LibDraw/Color.h>
 #include <LibDraw/Font.h>
 #include <LibDraw/Orientation.h>
+#include <LibDraw/Palette.h>
 #include <LibDraw/Rect.h>
 #include <LibDraw/SystemTheme.h>
 #include <LibGUI/GEvent.h>
@@ -22,7 +23,6 @@ class GLayout;
 class GMenu;
 class GWindow;
 class GraphicsBitmap;
-class Palette;
 
 enum class SizePolicy {
     Fixed,
@@ -237,7 +237,7 @@ public:
 
     void do_layout();
 
-    const Palette& palette() const { return *m_palette; }
+    Palette palette() const { return Palette(*m_palette); }
     void set_palette(const Palette&);
 
 protected:
@@ -301,7 +301,7 @@ private:
 
     HashMap<GShortcut, GAction*> m_local_shortcut_actions;
 
-    NonnullRefPtr<Palette> m_palette;
+    NonnullRefPtr<PaletteImpl> m_palette;
 };
 
 template<>