Add switch for "multiple windows" in Edit > Preferences > General

As the "multiple windows" feature is still buggy (#3556) and we've
disabled it by default, it's nice to make this option more visible (in
the General section) so users reliant on this will find the switch
quickly.

data/extensions/aseprite-theme/dark/theme.xml

@@ -444,6 +444,8 @@
         <part id="cursor_skew_e" x="288" y="176" w="16" h="16" focusx="8" focusy="8" />
         <part id="cursor_skew_nw" x="272" y="160" w="16" h="16" focusx="8" focusy="8" />
         <part id="cursor_skew_ne" x="288" y="160" w="16" h="16" focusx="8" focusy="8" />
+        <part id="one_win_icon" x="96" y="256" w="8" h="7" />
+        <part id="multi_win_icon" x="104" y="256" w="8" h="7" />
     </parts>
     <styles>
         <style id="box" />

data/extensions/aseprite-theme/theme.xml

@@ -440,6 +440,8 @@
         <part id="cursor_skew_e" x="288" y="176" w="16" h="16" focusx="8" focusy="8" />
         <part id="cursor_skew_nw" x="272" y="160" w="16" h="16" focusx="8" focusy="8" />
         <part id="cursor_skew_ne" x="288" y="160" w="16" h="16" focusx="8" focusy="8" />
+        <part id="one_win_icon" x="96" y="256" w="8" h="7" />
+        <part id="multi_win_icon" x="104" y="256" w="8" h="7" />
     </parts>
     <styles>
         <style id="box" />

data/strings/en.ini

@@ -1438,6 +1438,16 @@ section_theme = Theme
 section_extensions = Extensions
 section_experimental = Experimental
 general = General
+ui_windows = User Interface:
+one_win = <<<END
+Confine the user interface to one native window.
+i.e. Menus, Preview, popups are inside the main window area.
+END
+multi_win = <<<END
+Create one native window for each interface window.
+i.e. Menus, Preview, popups have their own window.
+END
+theme_mode = Theme Mode:
 screen_scaling = Screen Scaling:
 ui_scaling = UI Elements Scaling:
 language = Language:

data/widgets/options.xml

@@ -32,6 +32,18 @@
         <vbox id="section_general">
           <separator text="@.section_general" horizontal="true" />
           <grid columns="3">
+            <label text="@.ui_windows" />
+            <hbox>
+              <buttonset columns="2" id="ui_windows">
+                <item icon="one_win_icon" tooltip="@.one_win" tooltip_dir="bottom" />
+                <item icon="multi_win_icon" tooltip="@.multi_win" tooltip_dir="bottom" />
+              </buttonset>
+              <hbox id="theme_variants">
+                <label text="@.theme_mode" />
+              </hbox>
+            </hbox>
+            <boxfiller />
+
             <label text="@.screen_scaling" />
             <combobox id="screen_scale">
               <listitem text="100%" value="1" />
@@ -39,7 +51,7 @@
               <listitem text="300%" value="3" />
               <listitem text="400%" value="4" />
             </combobox>
-	    <hbox id="theme_variants" />
+            <boxfiller />
 
             <label text="@.ui_scaling" />
             <combobox id="ui_scale">

src/app/commands/cmd_options.cpp

@@ -484,6 +484,17 @@ public:
       gridScope()->Change.connect([this]{ onChangeGridScope(); });
     }
 
+    // Update the one/multiple window buttonset (and keep in on sync
+    // with the old/experimental checkbox)
+    uiWindows()->setSelectedItem(multipleWindows()->isSelected() ? 1: 0);
+    uiWindows()->ItemChange.connect([this]() {
+      multipleWindows()->setSelected(uiWindows()->selectedItem() == 1);
+    });
+    multipleWindows()->Click.connect([this](){
+      uiWindows()->setSelectedItem(multipleWindows()->isSelected() ? 1: 0);
+    });
+
+    // Scaling
     selectScalingItems();
 
 #ifdef _DEBUG // TODO enable this on Release when Aseprite supports
@@ -942,6 +953,7 @@ private:
       m_themeVars->deferDelete();
     }
     m_themeVars = list;
+    themeVariants()->setVisible(list ? true: false);
   }
 
   void fillExtensionsCombobox(ui::ComboBox* combobox,