creating HexContent and its ViewModel, ViewPort. I expect that HexContent will represent an area of the screen filled with hex data. There will probably be a wrapper panel that adds the scrollbar to the right and addresses to the left. ViewPort can act as the ViewModel for that entire panel. Added a failing test so I remember to go back and make the ViewModel notify when it's Width/Height gets changed.

Gen3Hex/Gen3Hex.csproj

@@ -47,19 +47,22 @@
     <Reference Include="PresentationFramework" />
   </ItemGroup>
   <ItemGroup>
-    <ApplicationDefinition Include="App.xaml">
+    <ApplicationDefinition Include="View\App.xaml">
       <Generator>MSBuild:Compile</Generator>
       <SubType>Designer</SubType>
     </ApplicationDefinition>
-    <Page Include="MainWindow.xaml">
+    <Compile Include="ViewModel\HexElement.cs" />
+    <Compile Include="ViewModel\ViewPort.cs" />
+    <Page Include="View\MainWindow.xaml">
       <Generator>MSBuild:Compile</Generator>
       <SubType>Designer</SubType>
     </Page>
-    <Compile Include="App.xaml.cs">
+    <Compile Include="View\App.xaml.cs">
       <DependentUpon>App.xaml</DependentUpon>
       <SubType>Code</SubType>
     </Compile>
-    <Compile Include="MainWindow.xaml.cs">
+    <Compile Include="View\HexContent.cs" />
+    <Compile Include="View\MainWindow.xaml.cs">
       <DependentUpon>MainWindow.xaml</DependentUpon>
       <SubType>Code</SubType>
     </Compile>

Gen3Hex/MainWindow.xaml

@@ -1,11 +0,0 @@
-<Window x:Class="HavenSoft.Gen3Hex.MainWindow"
-        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
-        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
-        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
-        mc:Ignorable="d"
-        Title="Gen3Hex" Height="450" Width="800">
-    <Grid>
-        
-    </Grid>
-</Window>

Gen3Hex/View/App.xaml

@@ -1,7 +1,7 @@
-<Application x:Class="HavenSoft.Gen3Hex.App"
+<Application x:Class="HavenSoft.Gen3Hex.View.App"
              xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
-             StartupUri="MainWindow.xaml">
+             StartupUri="View/MainWindow.xaml">
     <Application.Resources>
          
     </Application.Resources>

Gen3Hex/View/App.xaml.cs

@@ -2,7 +2,7 @@
 
 [assembly: AssemblyTitle("Gen3Hex")]
 
-namespace HavenSoft.Gen3Hex {
+namespace HavenSoft.Gen3Hex.View {
    public partial class App {
    }
 }

Gen3Hex/View/HexContent.cs

@@ -0,0 +1,82 @@
+using HavenSoft.Gen3Hex.ViewModel;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Globalization;
+using System.Linq;
+using System.Windows;
+using System.Windows.Media;
+
+namespace HavenSoft.Gen3Hex.View {
+   public class HexContent : FrameworkElement {
+      public const int
+         CellWidth = 30,
+         CellHeight = 20;
+
+      public const string Hex = "0123456789ABCDEF";
+
+      private readonly List<FormattedText> byteVisualCache = new List<FormattedText>();
+
+      private ViewPort ViewModel => (ViewPort)DataContext;
+
+      public HexContent() {
+         DataContextChanged += OnDataContextChanged;
+      }
+
+      protected override void OnRender(DrawingContext drawingContext) {
+         base.OnRender(drawingContext);
+
+         var viewPort = ViewModel;
+
+         VerifyByteVisualCache();
+
+         for (int x = 0; x < viewPort.Width; x++) {
+            for (int y = 0; y < viewPort.Height; y++) {
+               var element = viewPort[x, y];
+               drawingContext.DrawText(byteVisualCache[element.Value], new Point(x * CellWidth, y * CellHeight));
+            }
+         }
+      }
+
+      protected override void OnRenderSizeChanged(SizeChangedInfo sizeInfo) {
+         base.OnRenderSizeChanged(sizeInfo);
+
+         ViewModel.Width = (int)sizeInfo.NewSize.Width / CellWidth;
+         ViewModel.Height = (int)sizeInfo.NewSize.Height / CellHeight;
+      }
+
+      private void OnDataContextChanged(object sender, DependencyPropertyChangedEventArgs e) {
+         if (e.OldValue is INotifyPropertyChanged oldContext) {
+            oldContext.PropertyChanged -= OnDataContextPropertyChanged;
+         }
+
+         if(e.NewValue is INotifyPropertyChanged newContext) {
+            newContext.PropertyChanged += OnDataContextPropertyChanged;
+         }
+
+         this.InvalidateVisual();
+      }
+
+      private void OnDataContextPropertyChanged(object sender, PropertyChangedEventArgs e) {
+         if (e.PropertyName == nameof(ViewModel.Width) || e.PropertyName == nameof(ViewModel.Height)) {
+            this.InvalidateVisual();
+         }
+      }
+
+      private void VerifyByteVisualCache() {
+         if (byteVisualCache.Count != 0) return;
+
+         var bytesAsHex = Enumerable.Range(0, 255).Select(i => $"{Hex[i / 0x10]}{Hex[i % 0x10]}");
+
+         var text = bytesAsHex.Select(hex => new FormattedText(
+            hex,
+            CultureInfo.CurrentCulture,
+            FlowDirection.LeftToRight,
+            new Typeface("Consolas"),
+            16,
+            Brushes.Black,
+            1.0));
+
+         byteVisualCache.AddRange(text);
+      }
+   }
+}

Gen3Hex/View/MainWindow.xaml

@@ -0,0 +1,14 @@
+<Window x:Class="HavenSoft.Gen3Hex.View.MainWindow"
+        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        xmlns:hsg3hv="clr-namespace:HavenSoft.Gen3Hex.View"
+        xmlns:hsg3hvm="clr-namespace:HavenSoft.Gen3Hex.ViewModel"
+        Title="Gen3Hex" Height="450" Width="800">
+   <DockPanel>
+      <hsg3hv:HexContent>
+         <hsg3hv:HexContent.DataContext>
+            <hsg3hvm:ViewPort/>
+         </hsg3hv:HexContent.DataContext>
+      </hsg3hv:HexContent>
+   </DockPanel>
+</Window>

Gen3Hex/View/MainWindow.xaml.cs

@@ -1,4 +1,4 @@
-namespace HavenSoft.Gen3Hex {
+namespace HavenSoft.Gen3Hex.View {
    public partial class MainWindow {
       public MainWindow() => InitializeComponent();
    }

Gen3Hex/ViewModel/HexElement.cs

@@ -0,0 +1,5 @@
+namespace HavenSoft.Gen3Hex.ViewModel {
+   public class HexElement {
+      public byte Value { get; set; }
+   }
+}

Gen3Hex/ViewModel/ViewPort.cs

@@ -0,0 +1,13 @@
+using System.ComponentModel;
+
+namespace HavenSoft.Gen3Hex.ViewModel {
+   public class ViewPort : INotifyPropertyChanged {
+      public int Width { get; set; }
+
+      public int Height { get; set; }
+
+      public HexElement this[int x, int y] => new HexElement();
+
+      public event PropertyChangedEventHandler PropertyChanged;
+   }
+}

HexTests/Tests.cs

@@ -1,4 +1,5 @@
-using System.Reflection;
+using HavenSoft.Gen3Hex.ViewModel;
+using System.Reflection;
 using Xunit;
 
 [assembly: AssemblyTitle("HexTests")]
@@ -6,7 +7,15 @@ using Xunit;
 namespace HexTests {
    public class Tests {
       [Fact]
-      public void TestMethod1() {
+      public void ViewPortNotifiesOnSizeChange() {
+         var viewPort = new ViewPort();
+         var counter = 0;
+         viewPort.PropertyChanged += (sender, e) => counter++;
+
+         viewPort.Width = 12;
+         viewPort.Height = 50;
+
+         Assert.Equal(2, counter);
       }
    }
 }