Struct-valued custom enumerator for pixel offsets

Pinta.Core/Algorithms/ColorDifference.cs

@@ -35,7 +35,7 @@ public static void RenderColorDifferenceEffect (
 
 		foreach (RectangleI rect in rois) {
 
-			foreach (var pixel in Utility.GeneratePixelOffsets (rect, source.GetSize ())) {
+			foreach (var pixel in Tiling.GeneratePixelOffsets (rect, source.GetSize ())) {
 
 				destinationData[pixel.memoryOffset] = GetFinalPixelColor (
 					weights,

Pinta.Core/Algorithms/Utility.cs

@@ -38,27 +38,6 @@ public static double Magnitude (this PointI point)
 	public static double Distance (this PointD origin, in PointD dest)
 		=> Magnitude (origin - dest);
 
-	/// <returns>
-	/// Offsets of pixels, if we consider all pixels in a canvas of
-	/// size <paramref name="canvasSize"/> to be sequential in memory
-	/// (from left to right, and top to bottom)
-	/// </returns>
-	public static IEnumerable<PixelOffset> GeneratePixelOffsets (
-		this RectangleI roi,
-		Size canvasSize)
-	{
-		if (roi.Left < 0 || roi.Right >= canvasSize.Width || roi.Top < 0 || roi.Bottom >= canvasSize.Height)
-			throw new ArgumentException ($"Rectangle is out of size bounds");
-
-		for (int y = roi.Top; y <= roi.Bottom; y++) {
-			int rowOffset = y * canvasSize.Width;
-			for (int x = roi.Left; x <= roi.Right; x++)
-				yield return new (
-					coordinates: new (x, y),
-					memoryOffset: rowOffset + x);
-		}
-	}
-
 	public static PointD Lerp (
 		PointD from,
 		PointD to,

Pinta.Core/Enumeration/PixelOffsetEnumeration.cs

@@ -0,0 +1,86 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+
+namespace Pinta.Core;
+
+public readonly struct PixelOffsetEnumerable : IEnumerable<PixelOffset>
+{
+	private readonly RectangleI roi_bounds;
+	private readonly Size canvas_size;
+	internal PixelOffsetEnumerable (in RectangleI roiBounds, in Size canvasSize)
+	{
+		if (roiBounds.Left < 0 || roiBounds.Right >= canvasSize.Width || roiBounds.Top < 0 || roiBounds.Bottom >= canvasSize.Height)
+			throw new ArgumentException ($"Rectangle is out of size bounds");
+		roi_bounds = roiBounds;
+		canvas_size = canvasSize;
+	}
+
+	public PixelOffsetEnumerator GetEnumerator ()
+		=> new (roi_bounds, canvas_size);
+
+	IEnumerator IEnumerable.GetEnumerator () => GetEnumerator ();
+	IEnumerator<PixelOffset> IEnumerable<PixelOffset>.GetEnumerator () => GetEnumerator ();
+}
+
+public struct PixelOffsetEnumerator : IEnumerator<PixelOffset>
+{
+	private readonly Size canvas_size;
+	private readonly int left;
+	private readonly int right;
+	private readonly int top;
+	private readonly int bottom;
+	private int x;
+	private int y;
+	private int row_offset;
+	private bool has_more_rows;
+	internal PixelOffsetEnumerator (in RectangleI roiBounds, in Size canvasSize)
+	{
+		int l = roiBounds.Left;
+		int r = roiBounds.Right;
+		int t = roiBounds.Top;
+		int b = roiBounds.Bottom;
+
+		// --- Read-only
+		canvas_size = canvasSize;
+		left = l;
+		right = r;
+		top = t;
+		bottom = b;
+
+		// --- Mutable
+		x = l - 1; // Initialize to just before the first x
+		y = t;
+		row_offset = t * canvasSize.Width;
+		has_more_rows = t <= b;
+	}
+
+	public readonly PixelOffset Current => new (
+		coordinates: new PointI (x, y),
+		memoryOffset: row_offset + x);
+
+	public bool MoveNext ()
+	{
+		if (!has_more_rows) return false;
+		x++;
+		if (x <= right) return true;
+		x = left;
+		y++;
+		row_offset += canvas_size.Width;
+		if (y <= bottom) return true;
+		has_more_rows = false;
+		return false;
+	}
+
+	public void Reset ()
+	{
+		x = left - 1; // Initialize to just before the first x
+		y = top;
+		row_offset = top * canvas_size.Width;
+		has_more_rows = top <= bottom;
+	}
+
+	public void Dispose () { }
+
+	readonly object IEnumerator.Current => Current;
+}

Pinta.Core/Extensions/Tiling.cs

@@ -0,0 +1,12 @@
+namespace Pinta.Core;
+
+public static class Tiling
+{
+	/// <returns>
+	/// Offsets of pixels, if we consider all pixels in a canvas of
+	/// size <paramref name="canvasSize"/> to be sequential in memory
+	/// (from left to right, and top to bottom)
+	/// </returns>
+	public static PixelOffsetEnumerable GeneratePixelOffsets (this RectangleI bounds, Size canvasSize)
+		=> new (bounds, canvasSize);
+}

Pinta.Effects/Effects/AddNoiseEffect.cs

@@ -129,7 +129,7 @@ protected override void Render (
 		// being used to render the effect, but will change if the effect is tiled differently.
 		Random rand = new (settings.seed.GetValueForRegion (rect));
 
-		foreach (var pixel in Utility.GeneratePixelOffsets (rect, settings.size))
+		foreach (var pixel in Tiling.GeneratePixelOffsets (rect, settings.size))
 			destinationData[pixel.memoryOffset] = GetFinalPixelColor (
 				settings,
 				rand,

Pinta.Effects/Effects/BulgeEffect.cs

@@ -76,7 +76,7 @@ public override void Render (
 
 		foreach (RectangleI rect in rois) {
 
-			foreach (var pixel in Utility.GeneratePixelOffsets (rect, new Size (settings.sourceWidth, settings.sourceHeight))) {
+			foreach (var pixel in Tiling.GeneratePixelOffsets (rect, new Size (settings.sourceWidth, settings.sourceHeight))) {
 
 				destinationData[pixel.memoryOffset] = GetFinalPixelColor (
 					settings,

Pinta.Effects/Effects/DentsEffect.cs

@@ -82,7 +82,7 @@ public override void Render (ImageSurface src, ImageSurface dst, ReadOnlySpan<Re
 		Span<ColorBgra> dst_data = dst.GetPixelData ();
 		ReadOnlySpan<ColorBgra> src_data = src.GetReadOnlyPixelData ();
 		foreach (RectangleI rect in rois) {
-			foreach (var pixel in Utility.GeneratePixelOffsets (rect, src.GetSize ())) {
+			foreach (var pixel in Tiling.GeneratePixelOffsets (rect, src.GetSize ())) {
 				dst_data[pixel.memoryOffset] = Warp.GetPixelColor (
 					settings,
 					InverseTransform,

Pinta.Effects/Effects/DitheringEffect.cs

@@ -56,7 +56,7 @@ protected override void Render (ImageSurface src, ImageSurface dest, RectangleI
 			}
 		}
 
-		foreach (var pixel in Utility.GeneratePixelOffsets (roi, dest.GetSize ())) {
+		foreach (var pixel in Tiling.GeneratePixelOffsets (roi, dest.GetSize ())) {
 
 			ColorBgra originalPixel = dst_data[pixel.memoryOffset];
 			ColorBgra closestColor = FindClosestPaletteColor (settings.palette, originalPixel);

Pinta.Effects/Effects/FragmentEffect.cs

@@ -76,7 +76,7 @@ protected override void Render (
 		FragmentSettings settings = CreateSettings (source);
 		ReadOnlySpan<ColorBgra> sourceData = source.GetReadOnlyPixelData ();
 		Span<ColorBgra> dst_data = destination.GetPixelData ();
-		foreach (var pixel in Utility.GeneratePixelOffsets (roi, settings.sourceSize))
+		foreach (var pixel in Tiling.GeneratePixelOffsets (roi, settings.sourceSize))
 			dst_data[pixel.memoryOffset] = GetFinalPixelColor (
 				settings,
 				source,

Pinta.Effects/Effects/JuliaFractalEffect.cs

@@ -75,7 +75,7 @@ public override void Render (ImageSurface src, ImageSurface dst, ReadOnlySpan<Re
 		JuliaSettings settings = CreateSettings (dst);
 		Span<ColorBgra> dst_data = dst.GetPixelData ();
 		foreach (RectangleI rect in rois)
-			foreach (var pixel in Utility.GeneratePixelOffsets (rect, settings.canvasSize))
+			foreach (var pixel in Tiling.GeneratePixelOffsets (rect, settings.canvasSize))
 				dst_data[pixel.memoryOffset] = GetPixelColor (settings, pixel.coordinates);
 	}
 

Pinta.Effects/Effects/MandelbrotFractalEffect.cs

@@ -132,7 +132,7 @@ public override void Render (ImageSurface src, ImageSurface dst, ReadOnlySpan<Re
 		MandelbrotSettings settings = CreateSettings (dst);
 		Span<ColorBgra> dst_data = dst.GetPixelData ();
 		foreach (RectangleI rect in rois)
-			foreach (var pixel in Utility.GeneratePixelOffsets (rect, settings.canvasSize))
+			foreach (var pixel in Tiling.GeneratePixelOffsets (rect, settings.canvasSize))
 				dst_data[pixel.memoryOffset] = GetPixelColor (settings, pixel.coordinates);
 
 		if (settings.invertColors)

Pinta.Effects/Effects/MotionBlurEffect.cs

@@ -99,7 +99,7 @@ public override void Render (
 		Span<ColorBgra> dst_data = dst.GetPixelData ();
 
 		foreach (var rect in rois) {
-			foreach (var pixel in Utility.GeneratePixelOffsets (rect, settings.canvasSize)) {
+			foreach (var pixel in Tiling.GeneratePixelOffsets (rect, settings.canvasSize)) {
 				int sampleCount = 0;
 				for (int j = 0; j < settings.points.Length; ++j) {
 					PointD pt = new (settings.points[j].X + pixel.coordinates.X, settings.points[j].Y + pixel.coordinates.Y);

Pinta.Effects/Effects/OilPaintingEffect.cs

@@ -54,7 +54,7 @@ protected override void Render (
 		OilPaintingSettings settings = CreateSettings (source);
 		ReadOnlySpan<ColorBgra> src_data = source.GetReadOnlyPixelData ();
 		Span<ColorBgra> dst_data = destination.GetPixelData ();
-		foreach (var pixel in Utility.GeneratePixelOffsets (roi, settings.canvasSize))
+		foreach (var pixel in Tiling.GeneratePixelOffsets (roi, settings.canvasSize))
 			dst_data[pixel.memoryOffset] = GetFinalColor (
 				settings,
 				src_data,

Pinta.Effects/Effects/PencilSketchEffect.cs

@@ -72,7 +72,7 @@ public override void Render (ImageSurface src, ImageSurface dest, ReadOnlySpan<R
 		Size canvasSize = src.GetSize ();
 
 		foreach (RectangleI roi in rois) {
-			foreach (var pixel in Utility.GeneratePixelOffsets (roi, canvasSize)) {
+			foreach (var pixel in Tiling.GeneratePixelOffsets (roi, canvasSize)) {
 				ColorBgra srcGrey = desaturate_op.Apply (src_data[pixel.memoryOffset]);
 				dst_data[pixel.memoryOffset] = color_dodge_op.Apply (srcGrey, dst_data[pixel.memoryOffset]);
 			}

Pinta.Effects/Effects/PolarInversionEffect.cs

@@ -60,7 +60,7 @@ public override void Render (ImageSurface src, ImageSurface dst, ReadOnlySpan<Re
 		Span<ColorBgra> dst_data = dst.GetPixelData ();
 		ReadOnlySpan<ColorBgra> src_data = src.GetReadOnlyPixelData ();
 		foreach (RectangleI rect in rois) {
-			foreach (var pixel in Utility.GeneratePixelOffsets (rect, src.GetSize ())) {
+			foreach (var pixel in Tiling.GeneratePixelOffsets (rect, src.GetSize ())) {
 				dst_data[pixel.memoryOffset] = Warp.GetPixelColor (
 					settings,
 					InverseTransform,

Pinta.Effects/Effects/RadialBlurEffect.cs

@@ -86,7 +86,7 @@ public override void Render (ImageSurface source, ImageSurface destination, Read
 		Span<ColorBgra> destinationData = destination.GetPixelData ();
 
 		foreach (RectangleI rect in rois)
-			foreach (var pixel in Utility.GeneratePixelOffsets (rect, settings.canvasSize))
+			foreach (var pixel in Tiling.GeneratePixelOffsets (rect, settings.canvasSize))
 				destinationData[pixel.memoryOffset] = GetFinalPixelColor (
 					settings,
 					sourceData,

Pinta.Effects/Effects/SoftenPortraitEffect.cs

@@ -100,7 +100,7 @@ public override void Render (ImageSurface src, ImageSurface dest, ReadOnlySpan<R
 		Span<ColorBgra> dst_data = dest.GetPixelData ();
 
 		foreach (var roi in rois) {
-			foreach (var pixel in Utility.GeneratePixelOffsets (roi, src.GetSize ())) {
+			foreach (var pixel in Tiling.GeneratePixelOffsets (roi, src.GetSize ())) {
 				ColorBgra srcGrey = desaturate_op.Apply (src_data[pixel.memoryOffset]);
 				srcGrey.R = Utility.ClampToByte ((int) (srcGrey.R * settings.redAdjust));
 				srcGrey.B = Utility.ClampToByte ((int) (srcGrey.B * settings.blueAdjust));

Pinta.Effects/Effects/TileEffect.cs

@@ -125,7 +125,7 @@ protected override void Render (
 		TileSettings settings = CreateSettings (source);
 		ReadOnlySpan<ColorBgra> sourceData = source.GetReadOnlyPixelData ();
 		Span<ColorBgra> destinationData = destination.GetPixelData ();
-		foreach (var pixel in Utility.GeneratePixelOffsets (roi, source.GetSize ()))
+		foreach (var pixel in Tiling.GeneratePixelOffsets (roi, source.GetSize ()))
 			destinationData[pixel.memoryOffset] = GetFinalPixelColor (
 				source,
 				settings,

Pinta.Effects/Effects/TwistEffect.cs

@@ -51,7 +51,7 @@ protected override void Render (
 		TwistSettings settings = CreateSettings ();
 		ReadOnlySpan<ColorBgra> sourceData = source.GetReadOnlyPixelData ();
 		Span<ColorBgra> destinationData = destination.GetPixelData ();
-		foreach (var pixel in Utility.GeneratePixelOffsets (roi, source.GetSize ()))
+		foreach (var pixel in Tiling.GeneratePixelOffsets (roi, source.GetSize ()))
 			destinationData[pixel.memoryOffset] = GetFinalPixelColor (
 				settings,
 				source,

Pinta.Effects/Effects/VignetteEffect.cs

@@ -98,7 +98,7 @@ protected override void Render (
 		VignetteSettings settings = CreateSettings (source);
 		ReadOnlySpan<ColorBgra> sourceData = source.GetReadOnlyPixelData ();
 		Span<ColorBgra> destinationData = destination.GetPixelData ();
-		foreach (var pixel in Utility.GeneratePixelOffsets (roi, settings.canvasSize))
+		foreach (var pixel in Tiling.GeneratePixelOffsets (roi, settings.canvasSize))
 			destinationData[pixel.memoryOffset] = GetFinalPixelColor (settings, sourceData, pixel);
 	}
 

Pinta.Effects/Effects/ZoomBlurEffect.cs

@@ -76,7 +76,7 @@ protected override void Render (
 		ZoomBlurSettings settings = CreateSettings (source);
 		ReadOnlySpan<ColorBgra> sourceData = source.GetReadOnlyPixelData ();
 		Span<ColorBgra> destinationData = destination.GetPixelData ();
-		foreach (var pixel in Utility.GeneratePixelOffsets (roi, settings.size))
+		foreach (var pixel in Tiling.GeneratePixelOffsets (roi, settings.size))
 			destinationData[pixel.memoryOffset] = GetFinalPixelColor (
 				source,
 				settings,