Fix overlay scrollbar intercepting clicks on selection handles at image edges (#2200)

Author: AoMas17

Pinta.Core/Classes/IToolHandle.cs

@@ -14,6 +14,11 @@ public interface IToolHandle
 	/// </summary>
 	public bool Active { get; }
 
+	/// <summary>
+	/// Tests whether the window point is inside the handle's area.
+	/// </summary>
+	public bool ContainsPoint (PointD windowPoint);
+
 	/// <summary>
 	/// Draw the handle onto the canvas widget.
 	/// This is in window space, so CanvasPointToWindow() should be used to transform a canvas position

Pinta.Gui.Widgets/Widgets/Canvas/CanvasWindow.cs

@@ -25,6 +25,7 @@
 // THE SOFTWARE.
 
 using System;
+using System.Linq;
 using Pinta.Core;
 using Pinta.Gui.Widgets;
 
@@ -39,6 +40,8 @@ public sealed class CanvasWindow : Gtk.Grid
 	private readonly Ruler horizontal_ruler;
 	private readonly Ruler vertical_ruler;
 	private readonly Gtk.ScrolledWindow scrolled_window;
+	private readonly Gtk.Widget? horizontal_scrollbar;
+	private readonly Gtk.Widget? vertical_scrollbar;
 	private readonly Gtk.EventControllerMotion motion_controller;
 	private readonly Gtk.GestureDrag drag_controller;
 	private readonly Gtk.GestureZoom gesture_zoom;
@@ -143,6 +146,8 @@ public CanvasWindow (
 		vertical_ruler = verticalRuler;
 		motion_controller = motionController;
 		drag_controller = dragController;
+		horizontal_scrollbar = scrolledWindow.GetHscrollbar ();
+		vertical_scrollbar = scrolledWindow.GetVscrollbar ();
 
 		// --- Further initialization
 
@@ -190,6 +195,7 @@ private void HandleMotion (
 		current_canvas_pos = document.Workspace.ViewPointToCanvas (viewPos);
 		horizontal_ruler.Position = current_canvas_pos.X;
 		vertical_ruler.Position = current_canvas_pos.Y;
+		UpdateScrollbarTargeting (viewPos);
 
 		// Forward mouse move events to the current tool when not dragging.
 		if (drag_controller.GetStartPoint (out _, out _))
@@ -440,4 +446,16 @@ public bool DoKeyReleaseEvent (
 
 		return tools.DoKeyUp (document, tool_args);
 	}
+
+	private void UpdateScrollbarTargeting (PointD? viewPos = null)
+	{
+		bool canTarget = viewPos is null
+			|| tools.CurrentTool?.Handles.Any (h => h.Active && h.ContainsPoint (viewPos.Value)) != true;
+
+		if (horizontal_scrollbar is not null)
+			horizontal_scrollbar.CanTarget = canTarget;
+
+		if (vertical_scrollbar is not null)
+			vertical_scrollbar.CanTarget = canTarget;
+	}
 }

Pinta.Tools/Handles/LineHandle.cs

@@ -32,6 +32,9 @@ public LineHandle (IWorkspaceService workspace)
 		handles = [new MoveHandle (workspace), new MoveHandle (workspace)];
 	}
 
+	public bool ContainsPoint (PointD windowPoint)
+		=> handles.Any (c => c.ContainsPoint (windowPoint));
+
 	public void Draw (Snapshot snapshot)
 	{
 		foreach (MoveHandle handle in handles) {

Pinta.Tools/Handles/RectangleHandle.cs

@@ -54,6 +54,9 @@ public RectangleHandle (IWorkspaceService workspace)
 	#region IToolHandle Implementation
 	public bool Active { get; set; }
 
+	public bool ContainsPoint (PointD windowPoint)
+		=> handles.Values.Any (c => c.ContainsPoint (windowPoint));
+
 	public void Draw (Gtk.Snapshot snapshot)
 	{
 		foreach (MoveHandle handle in handles.Values)