Previous and applied selection are shown (#1454)

Pinta.Core/Classes/BaseTool.cs

@@ -28,6 +28,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
+using ClipperLib;
 using Gdk;
 using Gtk;
 
@@ -119,6 +120,16 @@ public virtual bool IsEditableShapeTool
 	public virtual IEnumerable<IToolHandle> Handles
 		=> [];
 
+	/// <summary>
+	/// For selection tools, returns the shape of the applied selection, i.e. the selection being combined with the previous selection.
+	/// When this method doesn't return null, a preview of the new selection is shown with the outlines of the previous and applied selection.
+	/// If this is not a selection tool, this should always return null
+	/// If this selection tool is not currently drawing a new selection or is in replace mode, this should return null.
+	/// </summary>
+	public virtual IReadOnlyList<IReadOnlyList<IntPoint>>? AppliedSelectionPolygons {
+		get => null;
+	}
+
 	/// <summary>
 	/// The shortcut key used to activate this tool in the toolbox.
 	/// Return Gdk.Key.Invalid for no shortcut key.

Pinta.Core/Classes/DocumentSelection.cs

@@ -129,7 +129,7 @@ public static List<List<IntPoint>> ConvertToPolygons (IReadOnlyList<IReadOnlyLis
 	/// </summary>
 	/// <param name="clipperPolygons">A Clipper Polygon collection.</param>
 	/// <returns>A Pinta Polygon set.</returns>
-	private static IReadOnlyList<IReadOnlyList<PointI>> ConvertToPolygonSet (IReadOnlyList<IReadOnlyList<IntPoint>> clipperPolygons)
+	public static IReadOnlyList<IReadOnlyList<PointI>> ConvertToPolygonSet (IReadOnlyList<IReadOnlyList<IntPoint>> clipperPolygons)
 	{
 		var resultingPolygonSet = new PointI[clipperPolygons.Count][];
 
@@ -152,6 +152,7 @@ private static IReadOnlyList<IReadOnlyList<PointI>> ConvertToPolygonSet (IReadOn
 		return resultingPolygonSet;
 	}
 
+
 	/// <summary>
 	/// Return a transformed copy of the selection.
 	/// </summary>

Pinta.Gui.Widgets/Widgets/Canvas/PintaCanvas.cs

@@ -27,6 +27,8 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using Cairo;
+using ClipperLib;
 using Pinta.Core;
 
 namespace Pinta.Gui.Widgets;
@@ -224,9 +226,24 @@ private void DrawSelection (Gtk.Snapshot snapshot, Graphene.Rect canvasViewBound
 		bool fillSelection = tools.CurrentTool?.IsSelectionTool ?? false;
 
 		// Convert the selection path.
-		Gsk.PathBuilder pathBuilder = Gsk.PathBuilder.New ();
-		pathBuilder.AddCairoPath (document.Selection.SelectionPath);
-		Gsk.Path selectionPath = pathBuilder.ToPath ();
+		Gsk.PathBuilder fillPathBuilder = Gsk.PathBuilder.New ();
+		fillPathBuilder.AddCairoPath (document.Selection.SelectionPath);
+		Gsk.Path fillPath = fillPathBuilder.ToPath ();
+
+		Gsk.Path strokePath;
+		IReadOnlyList<IReadOnlyList<IntPoint>>? appliedPolygons = tools.CurrentTool?.AppliedSelectionPolygons;
+		//appliedPolygons not null means the tool wants to show a preview.
+		if (appliedPolygons is not null) {
+			//The preview is composed of the outlines of the previous selection and the applied selection.
+			var previewPolygons = appliedPolygons.Concat (document.PreviousSelection.SelectionPolygons).ToList ();
+			using Context g = CairoExtensions.CreatePathContext ();
+			Path outlinePath = g.CreatePolygonPath (DocumentSelection.ConvertToPolygonSet (previewPolygons));
+
+			Gsk.PathBuilder strokePathBuilder = Gsk.PathBuilder.New ();
+			strokePathBuilder.AddCairoPath (outlinePath);
+			strokePath = strokePathBuilder.ToPath ();
+		} else
+			strokePath = fillPath;
 
 		snapshot.Save ();
 		snapshot.PushClip (canvasViewBounds);
@@ -238,18 +255,18 @@ private void DrawSelection (Gtk.Snapshot snapshot, Graphene.Rect canvasViewBound
 
 		if (fillSelection) {
 			Gdk.RGBA fillColor = new () { Red = 0.7f, Green = 0.8f, Blue = 0.9f, Alpha = 0.2f };
-			snapshot.AppendFill (selectionPath, Gsk.FillRule.EvenOdd, fillColor);
+			snapshot.AppendFill (fillPath, Gsk.FillRule.EvenOdd, fillColor);
 		}
 
 		// Draw a white line first so it shows up on dark backgrounds
 		Gsk.Stroke stroke = Gsk.Stroke.New (lineWidth: 1.0f / scale);
 		Gdk.RGBA white = new () { Red = 1, Green = 1, Blue = 1, Alpha = 1 };
-		snapshot.AppendStroke (selectionPath, stroke, white);
+		snapshot.AppendStroke (strokePath, stroke, white);
 
 		// Draw a black dashed line over the white line
 		stroke.SetDash ([2.0f / scale, 4.0f / scale]);
 		Gdk.RGBA black = new () { Red = 0, Green = 0, Blue = 0, Alpha = 1 };
-		snapshot.AppendStroke (selectionPath, stroke, black);
+		snapshot.AppendStroke (strokePath, stroke, black);
 
 		snapshot.Pop ();
 		snapshot.Restore ();

Pinta.Tools/Tools/LassoSelectTool.cs

@@ -155,6 +155,9 @@ private void FinalizeShape (Document document)
 			hist = null;
 		}
 		lasso_polygon.Clear ();
+
+		//To make sure the preview doesn't show anymore
+		document.Workspace.Invalidate ();
 	}
 
 	protected override void OnDeactivated (Document? document, BaseTool? newTool)
@@ -203,6 +206,9 @@ protected override void OnCommit (Document? document)
 			FinalizeShape (document);
 	}
 
+	public override List<List<IntPoint>>? AppliedSelectionPolygons =>
+		lasso_polygon.Count > 0 && combine_mode != CombineMode.Replace ? [lasso_polygon] : null;
+
 	protected override void OnSaveSettings (ISettingsService settings)
 	{
 		base.OnSaveSettings (settings);

Pinta.Tools/Tools/SelectTool.cs

@@ -28,6 +28,7 @@
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Linq;
+using ClipperLib;
 using Pinta.Core;
 
 namespace Pinta.Tools;
@@ -108,6 +109,7 @@ protected override void OnMouseMove (Document document, ToolMouseEventArgs e)
 
 		RectangleI dirty = ReDraw (document);
 
+
 		SelectionModeHandler.PerformSelectionMode (document, combine_mode, document.Selection.SelectionPolygons);
 		document.Workspace.Invalidate (dirty.Union (last_dirty));
 
@@ -180,6 +182,8 @@ private RectangleI ReDraw (Document document)
 
 		DrawShape (document, rect, document.Layers.SelectionLayer);
 
+		applied_selection_polygons = new List<List<IntPoint>> (document.Selection.SelectionPolygons);
+
 		// Figure out a bounding box for everything that was drawn, and add a bit of padding.
 		RectangleI dirty = rect.ToInt ();
 		dirty = dirty.Inflated (2, 2);
@@ -221,6 +225,10 @@ private void AfterSelectionChange (object? sender, EventArgs event_args)
 		LoadFromDocument (workspace.ActiveDocument);
 	}
 
+	private List<List<IntPoint>>? applied_selection_polygons = null;
+	public override List<List<IntPoint>>? AppliedSelectionPolygons =>
+		handle.IsDragging && combine_mode != CombineMode.Replace ? applied_selection_polygons : null;
+
 	/// <summary>
 	/// Initialize from the document's selection.
 	/// </summary>