Replace `ZoomFactors` with a plain `Dictionary`

src/BizHawk.Client.Common/Api/Classes/EmuClientApi.cs

@@ -121,7 +121,8 @@ namespace BizHawk.Client.Common
 
 		public int GetTargetScanlineIntensity() => _config.TargetScanlineFilterIntensity;
 
-		public int GetWindowSize() => _config.TargetZoomFactors[Emulator.SystemId];
+		public int GetWindowSize()
+			=> _config.GetWindowScaleFor(Emulator.SystemId);
 
 		public void InvisibleEmulation(bool invisible) => _mainForm.InvisibleEmulation = invisible;
 
@@ -194,7 +195,7 @@ namespace BizHawk.Client.Common
 		{
 			if (size == 1 || size == 2 || size == 3 || size == 4 || size == 5 || size == 10)
 			{
-				_config.TargetZoomFactors[Emulator.SystemId] = size;
+				_config.SetWindowScaleFor(Emulator.SystemId, size);
 				_mainForm.FrameBufferResized();
 				_displayManager.OSD.AddMessage($"Window size set to {size}x");
 			}

src/BizHawk.Client.Common/config/Config.cs

@@ -4,6 +4,7 @@ using System.IO;
 
 using BizHawk.Bizware.Graphics;
 using BizHawk.Common;
+using BizHawk.Common.CollectionExtensions;
 using BizHawk.Common.PathExtensions;
 using BizHawk.Emulation.Common;
 using BizHawk.Emulation.Cores;
@@ -96,7 +97,13 @@ namespace BizHawk.Client.Common
 
 		public bool StackOSDMessages { get; set; } = true;
 
-		public ZoomFactors TargetZoomFactors { get; set; } = new ZoomFactors();
+		private Dictionary<string, int> TargetZoomFactors { get; set; } = new();
+
+		public int GetWindowScaleFor(string sysID)
+			=> TargetZoomFactors.GetValueOrPut(sysID, static _ => 2);
+
+		public void SetWindowScaleFor(string sysID, int windowScale)
+			=> TargetZoomFactors[sysID] = windowScale;
 
 		// choose between 0 and 256
 		public int TargetScanlineFilterIntensity { get; set; } = 128;

src/BizHawk.Client.Common/config/ZoomFactors.cs

@@ -1,22 +0,0 @@
-using System.Collections.Generic;
-
-namespace BizHawk.Client.Common
-{
-	public class ZoomFactors : Dictionary<string, int>
-	{
-		public new int this[string index]
-		{
-			get
-			{
-				if (!ContainsKey(index))
-				{
-					Add(index, 2);
-				}
-
-				return base[index];
-			}
-
-			set => base[index] = value;
-		}
-	}
-}

src/BizHawk.Client.EmuHawk/MainForm.Events.cs

@@ -692,15 +692,16 @@ namespace BizHawk.Client.EmuHawk
 
 		private void WindowSizeSubMenu_DropDownOpened(object sender, EventArgs e)
 		{
+			var windowScale = Config.GetWindowScaleFor(Emulator.SystemId);
 			foreach (ToolStripMenuItem item in WindowSizeSubMenu.DropDownItems)
 			{
-				item.Checked = Config.TargetZoomFactors[Emulator.SystemId] == (int) item.Tag;
+				item.Checked = (int) item.Tag == windowScale;
 			}
 		}
 
 		private void WindowSize_Click(object sender, EventArgs e)
 		{
-			Config.TargetZoomFactors[Emulator.SystemId] = (int) ((ToolStripMenuItem) sender).Tag;
+			Config.SetWindowScaleFor(Emulator.SystemId, (int) ((ToolStripMenuItem) sender).Tag);
 			FrameBufferResized();
 		}
 

src/BizHawk.Client.EmuHawk/MainForm.cs

@@ -1381,7 +1381,7 @@ namespace BizHawk.Client.EmuHawk
 			// run this entire thing exactly twice, since the first resize may adjust the menu stacking
 			for (int i = 0; i < 2; i++)
 			{
-				int zoom = Config.TargetZoomFactors[Emulator.SystemId];
+				int zoom = Config.GetWindowScaleFor(Emulator.SystemId);
 				var area = Screen.FromControl(this).WorkingArea;
 
 				int borderWidth = Size.Width - _presentationPanel.Control.Size.Width;
@@ -2788,21 +2788,25 @@ namespace BizHawk.Client.EmuHawk
 
 		private void IncreaseWindowSize()
 		{
-			if (Config.TargetZoomFactors[Emulator.SystemId] < WINDOW_SCALE_MAX)
+			var windowScale = Config.GetWindowScaleFor(Emulator.SystemId);
+			if (windowScale < WINDOW_SCALE_MAX)
 			{
-				Config.TargetZoomFactors[Emulator.SystemId]++;
+				windowScale++;
+				Config.SetWindowScaleFor(Emulator.SystemId, windowScale);
 			}
-			AddOnScreenMessage($"Screensize set to {Config.TargetZoomFactors[Emulator.SystemId]}x");
+			AddOnScreenMessage($"Screensize set to {windowScale}x");
 			FrameBufferResized();
 		}
 
 		private void DecreaseWindowSize()
 		{
-			if (Config.TargetZoomFactors[Emulator.SystemId] > 1)
+			var windowScale = Config.GetWindowScaleFor(Emulator.SystemId);
+			if (windowScale > 1)
 			{
-				Config.TargetZoomFactors[Emulator.SystemId]--;
+				windowScale--;
+				Config.SetWindowScaleFor(Emulator.SystemId, windowScale);
 			}
-			AddOnScreenMessage($"Screensize set to {Config.TargetZoomFactors[Emulator.SystemId]}x");
+			AddOnScreenMessage($"Screensize set to {windowScale}x");
 			FrameBufferResized();
 		}
 

src/BizHawk.Tests/Client.Common/config/SerializationStabilityTests.cs

@@ -52,7 +52,6 @@ namespace BizHawk.Tests.Client.Common.config
 			[typeof(RewindConfig)] = @"{""UseCompression"":false,""UseDelta"":false,""Enabled"":true,""AllowSlowStates"":false,""BufferSize"":512,""UseFixedRewindInterval"":false,""TargetFrameLength"":600,""TargetRewindInterval"":5,""AllowOutOfOrderStates"":true,""BackingStore"":0}",
 			[typeof(SaveStateConfig)] = @"{""Type"":0,""CompressionLevelNormal"":1,""CompressionLevelRewind"":0,""MakeBackups"":true,""SaveScreenshot"":true,""BigScreenshotSize"":131072,""NoLowResLargeScreenshots"":false}",
 			[typeof(ToolDialogSettings)] = @"{""_wndx"":52,""_wndy"":44,""Width"":796,""Height"":455,""SaveWindowPosition"":true,""TopMost"":false,""FloatingWindow"":true,""AutoLoad"":false}",
-			[typeof(ZoomFactors)] = @"{""NULL"":2,""GB"":3}",
 			[typeof(ZwinderStateManagerSettings)] = ZWINDER_SER,
 		};