Use Fractions to represent zoom factor

The goal is to be able to get as close as possible to perfect 66.(6)% (2/3) zoom factor, and also remove types mismatch between the editor form and the surface.

Greenshot/Drawing/Surface.cs

@@ -307,15 +307,16 @@ namespace Greenshot.Drawing
 		[NonSerialized]
 		private Matrix _inverseZoomMatrix = new Matrix(1, 0, 0, 1, 0, 0);
 		[NonSerialized]
-		private float _zoomFactor = 1.0f;
+		private Fraction _zoomFactor = Fraction.Identity;
-		public float ZoomFactor
+		public Fraction ZoomFactor
 		{
 			get => _zoomFactor;
 			set
 			{
 				_zoomFactor = value;
+				var inverse = _zoomFactor.Inverse();
 				_zoomMatrix = new Matrix(_zoomFactor, 0, 0, _zoomFactor, 0, 0);
-				_inverseZoomMatrix = new Matrix(1f / _zoomFactor, 0, 0, 1f / _zoomFactor, 0, 0);
+				_inverseZoomMatrix = new Matrix(inverse, 0, 0, inverse, 0, 0);
 				UpdateSize();
 			}
 		}
@@ -1439,9 +1440,9 @@ namespace Greenshot.Drawing
 				LOG.Debug("Empty cliprectangle??");
 				return;
 			}
-			Rectangle imageClipRectangle = ZoomClipRectangle(targetClipRectangle, 1.0 / _zoomFactor, 2);
+			Rectangle imageClipRectangle = ZoomClipRectangle(targetClipRectangle, _zoomFactor.Inverse(), 2);
 
-			bool isZoomedIn = ZoomFactor > 1f;
+			bool isZoomedIn = _zoomFactor > Fraction.Identity;
 			if (_elements.HasIntersectingFilters(imageClipRectangle) || isZoomedIn)
 			{
 				if (_buffer != null)
@@ -1467,7 +1468,7 @@ namespace Greenshot.Drawing
 					//graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
 					DrawBackground(graphics, imageClipRectangle);
 					graphics.DrawImage(Image, imageClipRectangle, imageClipRectangle, GraphicsUnit.Pixel);
-					graphics.SetClip(ZoomClipRectangle(Rectangle.Round(targetGraphics.ClipBounds), 1.0 / _zoomFactor, 2));
+					graphics.SetClip(ZoomClipRectangle(Rectangle.Round(targetGraphics.ClipBounds), _zoomFactor.Inverse(), 2));
 					_elements.Draw(graphics, _buffer, RenderMode.EDIT, imageClipRectangle);
 				}
 				targetGraphics.ScaleTransform(_zoomFactor, _zoomFactor);

Greenshot/Forms/ImageEditorForm.Designer.cs

@@ -1718,7 +1718,7 @@ namespace Greenshot {
 			// 
 			this.zoom25MenuItem.Name = "zoom25MenuItem";
 			this.zoom25MenuItem.Size = new System.Drawing.Size(209, 22);
-			this.zoom25MenuItem.Tag = "25";
+			this.zoom25MenuItem.Tag = "1/4";
 			this.zoom25MenuItem.Text = "25%";
 			this.zoom25MenuItem.Click += new System.EventHandler(this.ZoomSetValueMenuItemClick);
 			// 
@@ -1726,7 +1726,7 @@ namespace Greenshot {
 			// 
 			this.zoom50MenuItem.Name = "zoom50MenuItem";
 			this.zoom50MenuItem.Size = new System.Drawing.Size(209, 22);
-			this.zoom50MenuItem.Tag = "50";
+			this.zoom50MenuItem.Tag = "1/2";
 			this.zoom50MenuItem.Text = "50%";
 			this.zoom50MenuItem.Click += new System.EventHandler(this.ZoomSetValueMenuItemClick);
 			// 
@@ -1734,7 +1734,7 @@ namespace Greenshot {
 			// 
 			this.zoom66MenuItem.Name = "zoom66MenuItem";
 			this.zoom66MenuItem.Size = new System.Drawing.Size(209, 22);
-			this.zoom66MenuItem.Tag = "66";
+			this.zoom66MenuItem.Tag = "2/3";
 			this.zoom66MenuItem.Text = "66%";
 			this.zoom66MenuItem.Click += new System.EventHandler(this.ZoomSetValueMenuItemClick);
 			// 
@@ -1742,7 +1742,7 @@ namespace Greenshot {
 			// 
 			this.zoom75MenuItem.Name = "zoom75MenuItem";
 			this.zoom75MenuItem.Size = new System.Drawing.Size(209, 22);
-			this.zoom75MenuItem.Tag = "75";
+			this.zoom75MenuItem.Tag = "3/4";
 			this.zoom75MenuItem.Text = "75%";
 			this.zoom75MenuItem.Click += new System.EventHandler(this.ZoomSetValueMenuItemClick);
 			// 
@@ -1757,7 +1757,7 @@ namespace Greenshot {
 			this.zoomActualSizeMenuItem.Name = "zoomActualSizeMenuItem";
 			this.zoomActualSizeMenuItem.ShortcutKeyDisplayString = "Ctrl+0";
 			this.zoomActualSizeMenuItem.Size = new System.Drawing.Size(209, 22);
-			this.zoomActualSizeMenuItem.Tag = "100";
+			this.zoomActualSizeMenuItem.Tag = "1/1";
 			this.zoomActualSizeMenuItem.Text = "100% - Actual Size";
 			this.zoomActualSizeMenuItem.Click += new System.EventHandler(this.ZoomSetValueMenuItemClick);
 			// 
@@ -1770,7 +1770,7 @@ namespace Greenshot {
 			// 
 			this.zoom200MenuItem.Name = "zoom200MenuItem";
 			this.zoom200MenuItem.Size = new System.Drawing.Size(209, 22);
-			this.zoom200MenuItem.Tag = "200";
+			this.zoom200MenuItem.Tag = "2/1";
 			this.zoom200MenuItem.Text = "200%";
 			this.zoom200MenuItem.Click += new System.EventHandler(this.ZoomSetValueMenuItemClick);
 			// 
@@ -1778,7 +1778,7 @@ namespace Greenshot {
 			// 
 			this.zoom300MenuItem.Name = "zoom300MenuItem";
 			this.zoom300MenuItem.Size = new System.Drawing.Size(209, 22);
-			this.zoom300MenuItem.Tag = "300";
+			this.zoom300MenuItem.Tag = "3/1";
 			this.zoom300MenuItem.Text = "300%";
 			this.zoom300MenuItem.Click += new System.EventHandler(this.ZoomSetValueMenuItemClick);
 			// 
@@ -1786,7 +1786,7 @@ namespace Greenshot {
 			// 
 			this.zoom400MenuItem.Name = "zoom400MenuItem";
 			this.zoom400MenuItem.Size = new System.Drawing.Size(209, 22);
-			this.zoom400MenuItem.Tag = "400";
+			this.zoom400MenuItem.Tag = "4/1";
 			this.zoom400MenuItem.Text = "400%";
 			this.zoom400MenuItem.Click += new System.EventHandler(this.ZoomSetValueMenuItemClick);
 			// 
@@ -1794,7 +1794,7 @@ namespace Greenshot {
 			// 
 			this.zoom600MenuItem.Name = "zoom600MenuItem";
 			this.zoom600MenuItem.Size = new System.Drawing.Size(209, 22);
-			this.zoom600MenuItem.Tag = "600";
+			this.zoom600MenuItem.Tag = "6/1";
 			this.zoom600MenuItem.Text = "600%";
 			this.zoom600MenuItem.Click += new System.EventHandler(this.ZoomSetValueMenuItemClick);
 			// 

Greenshot/Forms/ImageEditorForm.cs

@@ -69,8 +69,7 @@ namespace Greenshot {
 		/// <summary>
 		/// All provided zoom values (in percents) in ascending order.
 		/// </summary>
-		private readonly int[] ZOOM_VALUES = new[] { 25, 50, 66, 75, 100, 200, 300, 400, 600 };
+		private readonly Fraction[] ZOOM_VALUES = new Fraction[] { (1, 4), (1, 2), (2, 3), (3, 4), (1 ,1), (2, 1), (3, 1), (4, 1), (6, 1) };
-		private int _zoomValue = 100;
 
 		/// <summary>
 		/// An Implementation for the IImageEditor, this way Plugins have access to the HWND handles wich can be used with Win32 API calls.
@@ -1533,14 +1532,16 @@ namespace Greenshot {
 		}
 
 		private void ZoomInMenuItemClick(object sender, EventArgs e) {
-			var nextIndex = Array.FindIndex(ZOOM_VALUES, v => v > _zoomValue);
+			var zoomValue = Surface.ZoomFactor;
+			var nextIndex = Array.FindIndex(ZOOM_VALUES, v => v > zoomValue);
 			var nextValue = nextIndex < 0 ? ZOOM_VALUES[ZOOM_VALUES.Length - 1] : ZOOM_VALUES[nextIndex];
 
 			ZoomSetValue(nextValue);
 		}
 
 		private void ZoomOutMenuItemClick(object sender, EventArgs e) {
-			var nextIndex = Array.FindLastIndex(ZOOM_VALUES, v => v < _zoomValue);
+			var zoomValue = Surface.ZoomFactor;
+			var nextIndex = Array.FindLastIndex(ZOOM_VALUES, v => v < zoomValue);
 			var nextValue = nextIndex < 0 ? ZOOM_VALUES[0] : ZOOM_VALUES[nextIndex];
 
 			ZoomSetValue(nextValue);
@@ -1548,7 +1549,7 @@ namespace Greenshot {
 
 		private void ZoomSetValueMenuItemClick(object sender, EventArgs e) {
 			var senderMenuItem = (ToolStripMenuItem)sender;
-			int zoomPercent = int.Parse((string)senderMenuItem.Tag);
+			var zoomPercent = Fraction.Parse((string)senderMenuItem.Tag);
 
 			ZoomSetValue(zoomPercent);
 		}
@@ -1559,8 +1560,8 @@ namespace Greenshot {
 			var maxImageSize = maxWindowSize - chromeSize;
 			var imageSize = Surface.Image.Size;
 
-			static bool isFit(int zoom, int source, int boundary)
+			static bool isFit(Fraction scale, int source, int boundary)
-				=> source * zoom / 100 <= boundary;
+				=> (int)(source * scale) <= boundary;
 
 			var nextIndex = Array.FindLastIndex(
 				ZOOM_VALUES,
@@ -1572,7 +1573,7 @@ namespace Greenshot {
 			ZoomSetValue(nextValue);
 		}
 
-		private void ZoomSetValue(int value) {
+		private void ZoomSetValue(Fraction value) {
 			var surface = Surface as Surface;
 			var panel = surface?.Parent as Panel;
 			if (panel == null)
@@ -1596,14 +1597,13 @@ namespace Greenshot {
 			}
 
 			// Set the new zoom value
-			_zoomValue = value;
+			Surface.ZoomFactor = value;
-			Surface.ZoomFactor = 1f * value / 100;
 			Size = GetOptimalWindowSize();
 			AlignCanvasPositionAfterResize();
 
 			// Update zoom controls
-			string valueString = value.ToString();
+			zoomStatusDropDownBtn.Text = ((int)(100 * (double)value)).ToString() + "%";
-			zoomStatusDropDownBtn.Text = valueString + "%";
+			var valueString = value.ToString();
 			foreach (var item in zoomMenuStrip.Items) {
 				if (item is ToolStripMenuItem menuItem) {
 					menuItem.Checked = menuItem.Tag as string == valueString;

GreenshotPlugin/Core/Fraction.cs

@@ -0,0 +1,152 @@
+using System;
+using System.Text.RegularExpressions;
+
+namespace GreenshotPlugin.Core
+{
+    /// <summary>
+    /// Basic Fraction (Rational) numbers with features only needed to represent scale factors.
+    /// </summary>
+    public readonly struct Fraction : IEquatable<Fraction>, IComparable<Fraction>
+    {
+        public static Fraction Identity { get; } = new Fraction(1, 1);
+
+        public uint Numerator { get; }
+        public uint Denominator { get; }
+
+        public Fraction(uint numerator, uint denominator)
+        {
+            if (denominator == 0)
+            {
+                throw new ArgumentException("Can't divide by zero.", nameof(denominator));
+            }
+            if (numerator == 0)
+            {
+                throw new ArgumentException("Zero is not supported by this implementation.", nameof(numerator));
+            }
+            var gcd = GreatestCommonDivisor(numerator, denominator);
+            Numerator = numerator / gcd;
+            Denominator = denominator / gcd;
+        }
+
+        public Fraction Inverse()
+            => new Fraction(Denominator, Numerator);
+
+        #region Parse
+
+        private static readonly Regex PARSE_REGEX = new Regex(@"^([1-9][0-9]*)\/([1-9][0-9]*)$", RegexOptions.Compiled);
+        public static bool TryParse(string str, out Fraction result)
+        {
+            var match = PARSE_REGEX.Match(str);
+            if (!match.Success)
+            {
+                result = Identity;
+                return false;
+            }
+            var numerator = uint.Parse(match.Groups[1].Value);
+            var denominator = uint.Parse(match.Groups[2].Value);
+            result = new Fraction(numerator, denominator);
+            return true;
+        }
+
+        public static Fraction Parse(string str)
+            => TryParse(str, out var result)
+                ? result
+                : throw new ArgumentException($"Could not parse the input \"{str}\".", nameof(str));
+
+        #endregion
+
+        #region Overrides, interface implementations
+
+        public override string ToString()
+            => $"{Numerator}/{Denominator}";
+
+        public override bool Equals(object obj)
+            => obj is Fraction fraction && Equals(fraction);
+
+        public bool Equals(Fraction other)
+            => Numerator == other.Numerator && Denominator == other.Denominator;
+
+        public override int GetHashCode()
+        {
+            unchecked
+            {
+                int hashCode = -1534900553;
+                hashCode = hashCode * -1521134295 + Numerator.GetHashCode();
+                hashCode = hashCode * -1521134295 + Denominator.GetHashCode();
+                return hashCode;
+            }
+        }
+
+        public int CompareTo(Fraction other)
+            => (int)(Numerator * other.Denominator) - (int)(other.Numerator * Denominator);
+
+        #endregion
+
+        #region Equality operators
+
+        public static bool operator ==(Fraction left, Fraction right)
+            => left.Equals(right);
+
+        public static bool operator !=(Fraction left, Fraction right)
+            => !(left == right);
+
+        #endregion
+
+        #region Comparison operators
+
+        public static bool operator <(Fraction left, Fraction right)
+            => left.CompareTo(right) < 0;
+
+        public static bool operator <=(Fraction left, Fraction right)
+            => left.CompareTo(right) <= 0;
+
+        public static bool operator >(Fraction left, Fraction right)
+            => left.CompareTo(right) > 0;
+
+        public static bool operator >=(Fraction left, Fraction right)
+            => left.CompareTo(right) >= 0;
+
+        #endregion
+
+        #region Scale operators
+
+        public static Fraction operator *(Fraction left, Fraction right)
+            => new Fraction(left.Numerator * right.Numerator, left.Denominator * right.Denominator);
+
+        public static Fraction operator *(Fraction left, uint right)
+            => new Fraction(left.Numerator * right, left.Denominator);
+
+        public static Fraction operator *(uint left, Fraction right)
+            => new Fraction(left * right.Numerator, right.Denominator);
+
+        public static Fraction operator /(Fraction left, Fraction right)
+            => new Fraction(left.Numerator * right.Denominator, left.Denominator * right.Numerator);
+
+        public static Fraction operator /(Fraction left, uint right)
+            => new Fraction(left.Numerator, left.Denominator * right);
+
+        public static Fraction operator /(uint left, Fraction right)
+            => new Fraction(left * right.Denominator, right.Numerator);
+
+        #endregion
+
+        #region Type conversion operators
+
+        public static implicit operator double(Fraction fraction)
+            => 1.0 * fraction.Numerator / fraction.Denominator;
+
+        public static implicit operator float(Fraction fraction)
+            => 1.0f * fraction.Numerator / fraction.Denominator;
+
+        public static implicit operator Fraction(uint number)
+            => new Fraction(number, 1u);
+
+        public static implicit operator Fraction((uint numerator, uint demoninator) tuple)
+            => new Fraction(tuple.numerator, tuple.demoninator);
+
+        #endregion
+
+        private static uint GreatestCommonDivisor(uint a, uint b)
+            => (b != 0) ? GreatestCommonDivisor(b, a % b) : a;
+    }
+}

GreenshotPlugin/Interfaces/ISurface.cs

@@ -23,6 +23,7 @@ using System;
 using System.Drawing;
 using System.IO;
 using System.Windows.Forms;
+using GreenshotPlugin.Core;
 using GreenshotPlugin.Effects;
 using GreenshotPlugin.Interfaces.Drawing;
 
@@ -193,9 +194,9 @@ namespace GreenshotPlugin.Interfaces
         }
 
         /// <summary>
-        /// Zoom value applied to the surface. 1.0f for actual size (100%).
+        /// Zoom value applied to the surface.
         /// </summary>
-        float ZoomFactor { get; set; }
+        Fraction ZoomFactor { get; set; }
         /// <summary>
         /// Translate a point from image coorditate space to surface coordinate space.
         /// </summary>