Add the "align object" tool (#961)

* Move bound detection to a dedicated utility method: GetObjectBounds

* Basic implementation of align object

* Use a grid for the dialog

* Add support for aligning within a selection

* Move align object to the effects menu, under a new section "object"

* Add align object tests

* move feather effect to the object category

* use background color from selection

CHANGELOG.md

@@ -28,6 +28,7 @@ Thanks to the following contributors who worked on this release:
 - Added "Voronoi Diagram" effect (#692)
 - Ported "Vignette" and "Dents" effects from Paint.NET 3.36 (#881, #885)
 - Added "Feather" effect (#886, #953)
+- Added "Align object" effect (#936, #961)
 - Added support for exporting to portable pixmap (`.ppm`) files (#549)
   - Importing is not supported yet.
 - Added a nearest-neighbor resampling mode when resizing images (#596)

Pinta.Core/Actions/ImageActions.cs

@@ -212,73 +212,15 @@ private void HandlePintaCoreActionsImageCropToSelectionActivated (object sender,
 		CropImageToRectangle (doc, rect, doc.Selection.SelectionPath);
 	}
 
-	/// <summary>
-	/// Checks if all of the pixels in the row match the specified color.
-	/// </summary>
-	private static bool IsConstantRow (ImageSurface surf, Cairo.Color color, int y)
-	{
-		for (int x = 0; x < surf.Width; ++x) {
-			if (!color.Equals (surf.GetColorBgra (new (x, y)).ToCairoColor ()))
-				return false;
-		}
-
-		return true;
-	}
-
-	/// <summary>
-	/// Checks if all of the pixels in the column (within the bounds of the rectangle) match the specified color.
-	/// </summary>
-	private static bool IsConstantColumn (ImageSurface surf, Cairo.Color color, RectangleI rect, int x)
-	{
-		for (int y = rect.Top; y < rect.Bottom; ++y) {
-			if (!color.Equals (surf.GetColorBgra (new (x, y)).ToCairoColor ()))
-				return false;
-		}
-
-		return true;
-	}
-
 	private void HandlePintaCoreActionsImageAutoCropActivated (object sender, EventArgs e)
 	{
 		Document doc = workspace.ActiveDocument;
 
 		tools.Commit ();
 
 		var image = doc.GetFlattenedImage ();
-		RectangleI rect = image.GetBounds ();
-		Cairo.Color border_color = image.GetColorBgra (PointI.Zero).ToCairoColor ();
-
-		// Top down.
-		for (int y = 0; y < image.Height; ++y) {
-			if (!IsConstantRow (image, border_color, y))
-				break;
-
-			rect = rect with { Y = rect.Y + 1, Height = rect.Height - 1 };
-		}
-
-		// Bottom up.
-		for (int y = rect.Bottom; y >= rect.Top; --y) {
-			if (!IsConstantRow (image, border_color, y))
-				break;
-
-			rect = rect with { Height = rect.Height - 1 };
-		}
-
-		// Left side.
-		for (int x = 0; x < image.Width; ++x) {
-			if (!IsConstantColumn (image, border_color, rect, x))
-				break;
-
-			rect = rect with { X = rect.X + 1, Width = rect.Width - 1 };
-		}
-
-		// Right side.
-		for (int x = rect.Right; x >= rect.Left; --x) {
-			if (!IsConstantColumn (image, border_color, rect, x))
-				break;
 
-			rect = rect with { Width = rect.Width - 1 };
-		}
+		var rect = Utility.GetObjectBounds (image);
 
 		// Ignore the current selection when auto-cropping.
 		CropImageToRectangle (doc, rect, /*selection*/ null);

Pinta.Core/Effects/Utility.cs

@@ -9,6 +9,7 @@
 using System.Collections.Generic;
 using System.Numerics;
 using System.Reflection;
+using Cairo;
 
 namespace Pinta.Core;
 
@@ -480,4 +481,72 @@ public static RadiansAngle GetNearestStepAngle (RadiansAngle angle, int steps)
 
 		return new (sector);
 	}
+
+	/// <summary>
+	/// Checks if all of the pixels in the row match the specified color.
+	/// </summary>
+	private static bool IsConstantRow (ImageSurface surf, Cairo.Color color, RectangleI rect, int y)
+	{
+		for (int x = rect.Left; x < rect.Right; ++x) {
+			if (!color.Equals (surf.GetColorBgra (new (x, y)).ToCairoColor ()))
+				return false;
+		}
+
+		return true;
+	}
+
+	/// <summary>
+	/// Checks if all of the pixels in the column (within the bounds of the rectangle) match the specified color.
+	/// </summary>
+	private static bool IsConstantColumn (ImageSurface surf, Cairo.Color color, RectangleI rect, int x)
+	{
+		for (int y = rect.Top; y < rect.Bottom; ++y) {
+			if (!color.Equals (surf.GetColorBgra (new (x, y)).ToCairoColor ()))
+				return false;
+		}
+
+		return true;
+	}
+
+	public static RectangleI GetObjectBounds (ImageSurface image, RectangleI? searchArea = null)
+	{
+		// Use the entire image bounds by default, or restrict to the provided search area.
+		RectangleI rect = searchArea ?? image.GetBounds ();
+		// Get the background color from the top-left pixel of the rectangle
+		Cairo.Color borderColor = image.GetColorBgra (new PointI (rect.Left, rect.Top)).ToCairoColor ();
+
+		// Top down.
+		for (int y = rect.Top; y < rect.Bottom; ++y) {
+			if (!IsConstantRow (image, borderColor, rect, y))
+				break;
+
+			rect = rect with { Y = rect.Y + 1, Height = rect.Height - 1 };
+		}
+
+		// Bottom up.
+		for (int y = rect.Bottom - 1; y >= rect.Top; --y) {
+			if (!IsConstantRow (image, borderColor, rect, y))
+				break;
+
+			rect = rect with { Height = rect.Height - 1 };
+		}
+
+		// Left side.
+		for (int x = rect.Left; x < rect.Right; ++x) {
+			if (!IsConstantColumn (image, borderColor, rect, x))
+				break;
+
+			rect = rect with { X = rect.X + 1, Width = rect.Width - 1 };
+		}
+
+		// Right side.
+		for (int x = rect.Right - 1; x >= rect.Left; --x) {
+			if (!IsConstantColumn (image, borderColor, rect, x))
+				break;
+
+			rect = rect with { Width = rect.Width - 1 };
+		}
+
+		return rect;
+	}
 }

Pinta.Effects/CoreEffectsExtension.cs

@@ -57,6 +57,7 @@ public void Initialize ()
 
 		// Add the effects
 		PintaCore.Effects.RegisterEffect (new AddNoiseEffect (services));
+		PintaCore.Effects.RegisterEffect (new AlignObjectEffect (services));
 		PintaCore.Effects.RegisterEffect (new BulgeEffect (services));
 		PintaCore.Effects.RegisterEffect (new CloudsEffect (services));
 		PintaCore.Effects.RegisterEffect (new DentsEffect (services));
@@ -107,6 +108,7 @@ public void Uninitialize ()
 
 		// Remove the effects
 		PintaCore.Effects.UnregisterInstanceOfEffect (typeof (AddNoiseEffect));
+		PintaCore.Effects.UnregisterInstanceOfEffect (typeof (AlignObjectEffect));
 		PintaCore.Effects.UnregisterInstanceOfEffect (typeof (BulgeEffect));
 		PintaCore.Effects.UnregisterInstanceOfEffect (typeof (CloudsEffect));
 		PintaCore.Effects.UnregisterInstanceOfEffect (typeof (DentsEffect));

Pinta.Effects/Dialogs/Effects.AlignmentDialog.cs

@@ -0,0 +1,117 @@
+using System;
+using Gtk;
+using Pinta.Core;
+
+namespace Pinta.Effects;
+
+public sealed class AlignmentDialog : Gtk.Dialog
+{
+	private readonly Gtk.ToggleButton topLeft;
+	private readonly Gtk.ToggleButton topCenter;
+	private readonly Gtk.ToggleButton topRight;
+	private readonly Gtk.ToggleButton centerLeft;
+	private readonly Gtk.ToggleButton center;
+	private readonly Gtk.ToggleButton centerRight;
+	private readonly Gtk.ToggleButton bottomLeft;
+	private readonly Gtk.ToggleButton bottomCenter;
+	private readonly Gtk.ToggleButton bottomRight;
+
+	public AlignPosition SelectedPosition { get; private set; }
+
+	public event EventHandler? PositionChanged;
+
+	public AlignmentDialog (IChromeService chrome)
+	{
+		const int spacing = 6;
+
+		var grid = new Gtk.Grid {
+			RowSpacing = spacing,
+			ColumnSpacing = spacing,
+			RowHomogeneous = true,
+			ColumnHomogeneous = true,
+			MarginStart = 12,
+			MarginEnd = 12,
+			MarginTop = 12,
+			MarginBottom = 12
+		};
+
+		topLeft = CreateIconButton (Translations.GetString ("Top Left"), Resources.Icons.ResizeCanvasNW, AlignPosition.TopLeft);
+		topCenter = CreateIconButton (Translations.GetString ("Top Center"), Resources.Icons.ResizeCanvasUp, AlignPosition.TopCenter);
+		topRight = CreateIconButton (Translations.GetString ("Top Right"), Resources.Icons.ResizeCanvasNE, AlignPosition.TopRight);
+		centerLeft = CreateIconButton (Translations.GetString ("Center Left"), Resources.Icons.ResizeCanvasLeft, AlignPosition.CenterLeft);
+		center = CreateIconButton (Translations.GetString ("Center"), Resources.Icons.ResizeCanvasBase, AlignPosition.Center);
+		centerRight = CreateIconButton (Translations.GetString ("Center Right"), Resources.Icons.ResizeCanvasRight, AlignPosition.CenterRight);
+		bottomLeft = CreateIconButton (Translations.GetString ("Bottom Left"), Resources.Icons.ResizeCanvasSW, AlignPosition.BottomLeft);
+		bottomCenter = CreateIconButton (Translations.GetString ("Bottom Center"), Resources.Icons.ResizeCanvasDown, AlignPosition.BottomCenter);
+		bottomRight = CreateIconButton (Translations.GetString ("Bottom Right"), Resources.Icons.ResizeCanvasSE, AlignPosition.BottomRight);
+
+		// Add buttons to the grid
+		grid.Attach (topLeft, 0, 0, 1, 1);
+		grid.Attach (topCenter, 1, 0, 1, 1);
+		grid.Attach (topRight, 2, 0, 1, 1);
+		grid.Attach (centerLeft, 0, 1, 1, 1);
+		grid.Attach (center, 1, 1, 1, 1);
+		grid.Attach (centerRight, 2, 1, 1, 1);
+		grid.Attach (bottomLeft, 0, 2, 1, 1);
+		grid.Attach (bottomCenter, 1, 2, 1, 1);
+		grid.Attach (bottomRight, 2, 2, 1, 1);
+
+		// Set the default selection
+		SetSelectedPosition (AlignPosition.Center);
+
+		var content_area = this.GetContentAreaBox ();
+		content_area.Append (grid);
+
+		Title = Translations.GetString ("Align Object");
+
+		TransientFor = chrome.MainWindow;
+
+		Modal = true;
+
+		Resizable = false;
+
+		this.AddCancelOkButtons ();
+		this.SetDefaultResponse (Gtk.ResponseType.Ok);
+
+		Show ();
+	}
+
+	private Gtk.ToggleButton CreateIconButton (string tooltip, string iconName, AlignPosition position)
+	{
+		var button = new Gtk.ToggleButton ();
+		button.SetIconName (iconName);
+
+		button.TooltipText = tooltip;
+
+		button.OnClicked += (sender, args) => {
+			SetSelectedPosition (position);
+			PositionChanged?.Invoke (this, EventArgs.Empty);
+		};
+
+		return button;
+	}
+
+	private void SetSelectedPosition (AlignPosition position)
+	{
+		SelectedPosition = position;
+
+		topLeft.SetActive (position == AlignPosition.TopLeft);
+		topCenter.SetActive (position == AlignPosition.TopCenter);
+		topRight.SetActive (position == AlignPosition.TopRight);
+		centerLeft.SetActive (position == AlignPosition.CenterLeft);
+		center.SetActive (position == AlignPosition.Center);
+		centerRight.SetActive (position == AlignPosition.CenterRight);
+		bottomLeft.SetActive (position == AlignPosition.BottomLeft);
+		bottomCenter.SetActive (position == AlignPosition.BottomCenter);
+		bottomRight.SetActive (position == AlignPosition.BottomRight);
+	}
+
+	public void RunDialog ()
+	{
+		Present ();
+
+		this.OnResponse += (sender, args) => {
+			Destroy ();
+		};
+	}
+}