Fix a couple issues with the toolbars

- When the header bar is being used (Windows / Linux), avoid adding an empty main toolbar. This added a few pixels of unnecessary padding
- Similarly, omit the option to hide the main toolbar when the header bar is being used
- The tool's toolbar now scrolls horizontally if there are too many widgets (e.g. the line/curve tool)

Pinta.Core/Actions/ViewActions.cs

@@ -160,8 +160,10 @@ public void RegisterActions (Gtk.Application app, Gio.Menu menu)
 		app.AddAction (Rulers);
 		show_hide_menu.AppendItem (Rulers.CreateMenuItem ());
 
-		app.AddAction (ToolBar);
-		show_hide_menu.AppendItem (ToolBar.CreateMenuItem ());
+		if (PintaCore.Chrome.MainToolBar is not null) {
+			app.AddAction (ToolBar);
+			show_hide_menu.AppendItem (ToolBar.CreateMenuItem ());
+		}
 
 		app.AddAction (StatusBar);
 		show_hide_menu.AppendItem (StatusBar.CreateMenuItem ());

Pinta.Core/Extensions/GtkExtensions.cs

@@ -102,6 +102,15 @@ public static Gtk.Box CreateToolBar ()
 		return toolbar;
 	}
 
+	/// <summary>
+	/// Remove all child widgets from a box.
+	/// </summary>
+	public static void RemoveAll (this Gtk.Box box)
+	{
+		while (box.GetFirstChild () is Widget child)
+			box.Remove (child);
+	}
+
 	public static Gtk.Button CreateToolBarItem (this Command action, bool force_icon_only = false)
 	{
 		var label = action.ShortLabel ?? action.Label;

Pinta.Core/Managers/ChromeManager.cs

@@ -45,7 +45,7 @@ public sealed class ChromeManager
 	private MessageDialogHandler message_dialog_handler = null!;
 	private SimpleEffectDialogHandler simple_effect_dialog_handler = null!;
 
-	public Box MainToolBar { get; private set; } = null!;
+	public Box? MainToolBar { get; private set; }
 	public Box ToolToolBar { get; private set; } = null!;
 	public Box ToolBox { get; private set; } = null!;
 	public Box StatusBar { get; private set; } = null!;

Pinta.Core/Managers/ToolManager.cs

@@ -194,7 +194,8 @@ public void SetCurrentTool (BaseTool tool)
 		PintaCore.Chrome.ToolToolBar.Append (ToolImage);
 		PintaCore.Chrome.ToolToolBar.Append (ToolSeparator);
 
-		tool.DoBuildToolBar (PintaCore.Chrome.ToolToolBar);
+		PintaCore.Chrome.ToolToolBar.Append (ToolWidgetsScroll);
+		tool.DoBuildToolBar (ToolWidgetsBox);
 
 		PintaCore.Workspace.Invalidate ();
 		PintaCore.Chrome.SetStatusBarText ($" {tool.Name}: {tool.StatusBarText}");
@@ -242,12 +243,10 @@ public bool SetCurrentTool (Gdk.Key shortcut)
 		return shortcut_tools[next_index];
 	}
 
-	private static void DeactivateTool (BaseTool tool, BaseTool? newTool)
+	private void DeactivateTool (BaseTool tool, BaseTool? newTool)
 	{
-		var toolbar = PintaCore.Chrome.ToolToolBar;
-
-		while (toolbar.GetFirstChild () is Widget child)
-			toolbar.Remove (child);
+		ToolWidgetsBox.RemoveAll ();
+		PintaCore.Chrome.ToolToolBar.RemoveAll ();
 
 		tool.DoDeactivated (PintaCore.Workspace.ActiveDocumentOrDefault, newTool);
 		tool.ToolItem.Active = false;
@@ -350,8 +349,22 @@ public override int Compare (BaseTool? x, BaseTool? y)
 	private Label? tool_label;
 	private Image? tool_image;
 	private Separator? tool_sep;
+	private Box? tool_widgets_box;
+	private ScrolledWindow? tool_widgets_scroll;
 
 	private Label ToolLabel => tool_label ??= Label.New (string.Format (" {0}:  ", Translations.GetString ("Tool")));
 	private Image ToolImage => tool_image ??= new Image ();
 	private Separator ToolSeparator => tool_sep ??= GtkExtensions.CreateToolBarSeparator ();
+	private Box ToolWidgetsBox => tool_widgets_box ??= Gtk.Box.New (Orientation.Horizontal, 0);
+	// Scroll the toolbar contents if they are very long (e.g. the line/curve tool).
+	private ScrolledWindow ToolWidgetsScroll => tool_widgets_scroll ??= new ScrolledWindow () {
+		Child = ToolWidgetsBox,
+		HscrollbarPolicy = PolicyType.Automatic,
+		VscrollbarPolicy = PolicyType.Never,
+		HasFrame = false,
+		OverlayScrolling = true,
+		WindowPlacement = CornerType.BottomRight,
+		Hexpand = true,
+		Halign = Align.Fill
+	};
 }

Pinta/Actions/View/ToolBarToggledAction.cs

@@ -44,6 +44,7 @@ public void Uninitialize ()
 
 	private void Activated (bool value)
 	{
-		PintaCore.Chrome.MainToolBar.Visible = value;
+		if (PintaCore.Chrome.MainToolBar is not null)
+			PintaCore.Chrome.MainToolBar.Visible = value;
 	}
 }

Pinta/MainWindow.cs

@@ -394,20 +394,18 @@ private void CreateMainMenu (WindowShell shell)
 
 	private void CreateMainToolBar (WindowShell shell)
 	{
-		var main_toolbar = window_shell.CreateToolBar ("main_toolbar");
-
 		if (window_shell.HeaderBar is not null)
 			PintaCore.Actions.CreateHeaderToolBar (window_shell.HeaderBar!);
-		else
+		else {
+			var main_toolbar = window_shell.CreateToolBar ("main_toolbar");
 			PintaCore.Actions.CreateToolBar (main_toolbar);
-
-		PintaCore.Chrome.InitializeMainToolBar (main_toolbar);
+		}
 	}
 
 	private void CreateToolToolBar (WindowShell shell)
 	{
 		var tool_toolbar = window_shell.CreateToolBar ("tool_toolbar");
-		tool_toolbar.HeightRequest = 42;
+		tool_toolbar.HeightRequest = 48;
 
 		PintaCore.Chrome.InitializeToolToolBar (tool_toolbar);
 	}