Idk what I'm doing

src/.idea/.idea.PixiEditorPrototype/.idea/.gitignore

@@ -0,0 +1,13 @@
+# Default ignored files
+/shelf/
+/workspace.xml
+# Rider ignored files
+/.idea.PixiEditorPrototype.iml
+/modules.xml
+/projectSettingsUpdater.xml
+/contentModel.xml
+# Editor-based HTTP Client requests
+/httpRequests/
+# Datasource local storage ignored files
+/dataSources/
+/dataSources.local.xml

src/.idea/.idea.PixiEditorPrototype/.idea/deployment.xml

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+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/Models/BlendModeEx.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/Models/DocumentHelpers.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/Models/DocumentState.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/Models/DocumentStructureHelper.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/Models/DocumentUpdater.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/Models/IReadOnlyListEx.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/Models/RefreshViewport_PassthroughAction.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/Models/RemoveViewport_PassthroughAction.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/Models/Rendering/AffectedChunkGatherer.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/Models/Rendering/RenderInfos/DirtyRect_RenderInfo.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/Models/Rendering/RenderInfos/IRenderInfo.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/Models/Rendering/RenderInfos/MaskPreviewDirty_RenderInfo.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/Models/Rendering/RenderInfos/PreviewDirty_RenderInfo.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/Models/Rendering/WriteableBitmapUpdater.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/Models/Tool.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/Models/ViewportLocation.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/PixiEditorPrototype.csproj" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/RelayCommand.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/ReverseOrderStackPanel.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/UserControls/Viewport/Viewport.xaml" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/UserControls/Viewport/Viewport.xaml.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/ViewModels/DocumentTransformViewModel.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/ViewModels/DocumentViewModel.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/ViewModels/FolderViewModel.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/ViewModels/LayerViewModel.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/ViewModels/StructureMemberViewModel.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/ViewModels/ViewModelMain.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/Views/MainWindow.xaml" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/Views/MainWindow.xaml.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/obj/Debug/net6.0-windows/App.g.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/obj/Debug/net6.0-windows/GeneratedInternalTypeHelper.g.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/obj/Debug/net6.0-windows/PixiEditorPrototype.AssemblyInfo.cs" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/obj/Debug/net6.0-windows/PixiEditorPrototype.GeneratedMSBuildEditorConfig.editorconfig" web="/" />
+            <mapping local="$PROJECT_DIR$/PixiEditorPrototype/obj/Debug/net6.0-windows/Views/MainWindow.g.cs" web="/" />
+            <mapping local="$PROJECT_DIR$" web="/" />
+          </mappings>
+        </serverdata>
+      </paths>
+    </serverData>
+  </component>
+</project>

src/.idea/.idea.PixiEditorPrototype/.idea/indexLayout.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="UserContentModel">
+    <attachedFolders />
+    <explicitIncludes />
+    <explicitExcludes />
+  </component>
+</project>

src/ChunkyImageLib/Surface.cs

@@ -8,9 +8,9 @@ namespace ChunkyImageLib;
 public class Surface : IDisposable
 {
     private bool disposed;
-    private int bytesPerPixel;
     public IntPtr PixelBuffer { get; }
     public SKSurface SkiaSurface { get; }
+    public int BytesPerPixel { get; }
     public VecI Size { get; }
 
     private SKPaint drawingPaint = new SKPaint() { BlendMode = SKBlendMode.Src };
@@ -24,8 +24,8 @@ public class Surface : IDisposable
 
         Size = size;
 
-        bytesPerPixel = 8;
-        PixelBuffer = CreateBuffer(size.X, size.Y, bytesPerPixel);
+        BytesPerPixel = 8;
+        PixelBuffer = CreateBuffer(size.X, size.Y, BytesPerPixel);
         SkiaSurface = CreateSKSurface();
     }
 
@@ -50,7 +50,7 @@ public class Surface : IDisposable
     {
         if (other.Size != Size)
             throw new ArgumentException("Target Surface must have the same dimensions");
-        int bytesC = Size.X * Size.Y * bytesPerPixel;
+        int bytesC = Size.X * Size.Y * BytesPerPixel;
         using var pixmap = other.SkiaSurface.PeekPixels();
         Buffer.MemoryCopy((void*)PixelBuffer, (void*)pixmap.GetPixels(), bytesC, bytesC);
     }
@@ -60,7 +60,7 @@ public class Surface : IDisposable
     /// </summary>
     public unsafe SKColor GetSRGBPixel(VecI pos)
     {
-        Half* ptr = (Half*)(PixelBuffer + (pos.X + pos.Y * Size.X) * bytesPerPixel);
+        Half* ptr = (Half*)(PixelBuffer + (pos.X + pos.Y * Size.X) * BytesPerPixel);
         float a = (float)ptr[3];
         return (SKColor)new SKColorF((float)ptr[0] / a, (float)ptr[1] / a, (float)ptr[2] / a, (float)ptr[3]);
     }

src/PixiEditor.ChangeableDocument.Gen/Helpers.cs

@@ -14,20 +14,23 @@ internal static class Helpers
         List<TypeWithName> constructorArgs = changeConstructorInfo.Arguments;
         List<TypeWithName> properties = constructorArgs.Select(static typeWithName =>
             {
-                return new TypeWithName(typeWithName.Type, typeWithName.FullNamespace, VariableNameIntoPropertyName(typeWithName.Name));
+                return new TypeWithName(typeWithName.Type, typeWithName.FullNamespace, VariableNameIntoPropertyName(typeWithName.Name), typeWithName.Nullable);
             }).ToList();
 
         var propToVar = MatchMembers(properties, constructorArgs);
 
         StringBuilder sb = new();
-
-        sb.AppendLine("namespace PixiEditor.ChangeableDocument.Actions.Generated;");
+         
+        sb.AppendLine("namespace PixiEditor.ChangeableDocument.Actions.Generated;\n");
+        sb.AppendLine("[System.Runtime.CompilerServices.CompilerGenerated]");
         sb.AppendLine($"public record class {actionName} : PixiEditor.ChangeableDocument.Actions.IMakeChangeAction");
         sb.AppendLine("{");
         sb.Append($"public {actionName}");
         AppendArgumentList(sb, constructorArgs);
         AppendConstructorBody(sb, propToVar);
+        sb.AppendLine("// Properties");
         AppendProperties(sb, properties);
+        sb.AppendLine("// Changes");
         AppendCreateCorrespondingChange(sb, changeConstructorInfo.ContainingClass, properties);
         sb.AppendLine("}");
 
@@ -41,7 +44,7 @@ internal static class Helpers
         List<TypeWithName> constructorArgs = changeConstructorInfo.Arguments;
         List<TypeWithName> properties = constructorArgs.Select(static typeWithName =>
         {
-            return new TypeWithName(typeWithName.Type, typeWithName.FullNamespace, VariableNameIntoPropertyName(typeWithName.Name));
+            return new TypeWithName(typeWithName.Type, typeWithName.FullNamespace, VariableNameIntoPropertyName(typeWithName.Name), typeWithName.Nullable);
         }).ToList();
 
         var constructorAssignments = MatchMembers(properties, constructorArgs);
@@ -94,7 +97,8 @@ public record class {actionName} : PixiEditor.ChangeableDocument.Actions.IEndCha
             return new TypeWithName(
                 parameter.Type.ToDisplayString(TypeWithGenerics),
                 parameter.Type.ContainingNamespace.ToDisplayString(),
-                parameter.Name
+                parameter.Name,
+                parameter.NullableAnnotation is NullableAnnotation.Annotated
                 );
         }).ToList();
         string changeName = method.ContainingType.Name;
@@ -136,7 +140,14 @@ public record class {actionName} : PixiEditor.ChangeableDocument.Actions.IEndCha
         sb.Append("(");
         for (int i = 0; i < variables.Count; i++)
         {
-            sb.Append(variables[i].TypeWithNamespace).Append(" ").Append(variables[i].Name);
+            sb.Append(variables[i].TypeWithNamespace);
+
+            if (variables[i].Nullable)
+            {
+                sb.Append("?");
+            }
+            
+            sb.Append(" ").Append(variables[i].Name);
             if (i != variables.Count - 1)
                 sb.Append(", ");
         }
@@ -195,7 +206,7 @@ public record class {actionName} : PixiEditor.ChangeableDocument.Actions.IEndCha
     {
         foreach (var typeWithName in properties)
         {
-            sb.AppendLine($"public {typeWithName.TypeWithNamespace} {typeWithName.Name} {{ get; init; }}");
+            sb.AppendLine($"public {typeWithName.TypeWithNamespace}{(typeWithName.Nullable ? "?" : "")} {typeWithName.Name} {{ get; init; }}");
         }
     }
 

src/PixiEditor.ChangeableDocument.Gen/TypeWithName.cs

@@ -1,15 +1,17 @@
 namespace PixiEditor.ChangeableDocument.Gen;
 internal struct TypeWithName
 {
-    public TypeWithName(string type, string fullNamespace, string name)
+    public TypeWithName(string type, string fullNamespace, string name, bool nullable)
     {
         Type = type;
         FullNamespace = fullNamespace;
         Name = name;
+        Nullable = nullable;
     }
 
     public string Type { get; }
     public string FullNamespace { get; }
     public string TypeWithNamespace => FullNamespace + "." + Type;
     public string Name { get; }
+    public bool Nullable { get; }
 }

src/PixiEditor.ChangeableDocument/ChangeInfos/Structure/CreateReferenceLayer_ChangeInfo.cs

@@ -0,0 +1,3 @@
+namespace PixiEditor.ChangeableDocument.ChangeInfos.Structure;
+
+public record class CreateReferenceLayer_ChangeInfo(bool ShapeOnly) : IChangeInfo;

src/PixiEditor.ChangeableDocument/ChangeInfos/Structure/TransformReferenceLayer_ChangeInfo.cs

@@ -0,0 +1,3 @@
+namespace PixiEditor.ChangeableDocument.ChangeInfos.Structure;
+
+public record class TransformReferenceLayer_ChangeInfo(ShapeCorners Shape) : IChangeInfo;

src/PixiEditor.ChangeableDocument/Changeables/Document.cs

@@ -1,4 +1,5 @@
 using PixiEditor.ChangeableDocument.Changeables.Interfaces;
+using SkiaSharp;
 
 namespace PixiEditor.ChangeableDocument.Changeables;
 
@@ -11,9 +12,12 @@ internal class Document : IChangeable, IReadOnlyDocument, IDisposable
     IReadOnlyStructureMember IReadOnlyDocument.FindMemberOrThrow(Guid guid) => FindMemberOrThrow(guid);
     (IReadOnlyStructureMember, IReadOnlyFolder) IReadOnlyDocument.FindChildAndParentOrThrow(Guid guid) => FindChildAndParentOrThrow(guid);
 
+    IReadOnlyReferenceLayer? IReadOnlyDocument.GetReferenceLayer() => ReferenceLayer;
+    
     public static VecI DefaultSize { get; } = new VecI(64, 64);
     internal Folder StructureRoot { get; } = new() { GuidValue = Guid.Empty };
     internal Selection Selection { get; } = new();
+    internal ReferenceLayer? ReferenceLayer { get; set; }
     public VecI Size { get; set; } = DefaultSize;
     public bool HorizontalSymmetryAxisEnabled { get; set; }
     public bool VerticalSymmetryAxisEnabled { get; set; }

src/PixiEditor.ChangeableDocument/Changeables/Interfaces/IReadOnlyDocument.cs

@@ -13,4 +13,5 @@ public interface IReadOnlyDocument
     IReadOnlyStructureMember FindMemberOrThrow(Guid guid);
     (IReadOnlyStructureMember, IReadOnlyFolder) FindChildAndParentOrThrow(Guid guid);
     IReadOnlyList<IReadOnlyStructureMember> FindMemberPath(Guid guid);
+    IReadOnlyReferenceLayer? GetReferenceLayer();
 }

src/PixiEditor.ChangeableDocument/Changeables/Interfaces/IReadOnlyReferenceLayer.cs

@@ -0,0 +1,10 @@
+using SkiaSharp;
+
+namespace PixiEditor.ChangeableDocument.Changeables.Interfaces;
+
+public interface IReadOnlyReferenceLayer
+{
+    public Surface Image { get; }
+    
+    public ShapeCorners Shape { get; }
+}

src/PixiEditor.ChangeableDocument/Changeables/ReferenceLayer.cs

@@ -0,0 +1,17 @@
+using PixiEditor.ChangeableDocument.Changeables.Interfaces;
+using SkiaSharp;
+
+namespace PixiEditor.ChangeableDocument.Changeables;
+
+public class ReferenceLayer : IReadOnlyReferenceLayer
+{
+    public Surface Image { get; }
+    
+    public ShapeCorners Shape { get; set; }
+
+    public ReferenceLayer(Surface image, ShapeCorners shape)
+    {
+        Image = image;
+        Shape = shape;
+    }
+}

src/PixiEditor.ChangeableDocument/Changes/Root/CreateReferenceLayer_UpdateableChange.cs

@@ -0,0 +1,51 @@
+using PixiEditor.ChangeableDocument.ChangeInfos.Structure;
+
+namespace PixiEditor.ChangeableDocument.Changes.Root;
+
+internal class CreateReferenceLayer_UpdateableChange : UpdateableChange
+{
+    private readonly Surface? surface;
+    private ShapeCorners shape;
+    
+    [GenerateUpdateableChangeActions]
+    public CreateReferenceLayer_UpdateableChange(Surface? surface, ShapeCorners shape)
+    {
+        this.surface = surface;
+        this.shape = shape;
+    }
+
+    [UpdateChangeMethod]
+    public void Update(ShapeCorners shape)
+    {
+        this.shape = shape;
+    }
+    
+    public override OneOf<Success, Error> InitializeAndValidate(Document target)
+    {
+        if (surface == null)
+        {
+            return new Error();
+        }
+        
+        target.ReferenceLayer = new ReferenceLayer(surface!, shape);
+        return new Success();
+    }
+
+    public override OneOf<None, IChangeInfo, List<IChangeInfo>> Apply(Document target, out bool ignoreInUndo)
+    {
+        target.ReferenceLayer!.Shape = shape;
+        ignoreInUndo = true;
+        return new CreateReferenceLayer_ChangeInfo(true);
+    }
+
+    public override OneOf<None, IChangeInfo, List<IChangeInfo>> Revert(Document target)
+    {
+        throw new NotImplementedException();
+    }
+
+    public override OneOf<None, IChangeInfo, List<IChangeInfo>> ApplyTemporarily(Document target)
+    {
+        target.ReferenceLayer!.Shape = shape;
+        return new CreateReferenceLayer_ChangeInfo(true);
+    }
+}

src/PixiEditorPrototype/Helpers/SurfaceHelpers.cs

@@ -0,0 +1,42 @@
+using System;
+using System.Windows;
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+using ChunkyImageLib;
+using SkiaSharp;
+
+namespace PixiEditorPrototype.Helpers;
+
+public static class SurfaceHelpers
+{
+    public static WriteableBitmap ToWriteableBitmap(this Surface surface)
+    {
+        int width = surface.Size.X;
+        int height = surface.Size.Y;
+        WriteableBitmap result = new WriteableBitmap(width, height, 96, 96, PixelFormats.Pbgra32, null);
+        result.Lock();
+        var dirty = new Int32Rect(0, 0, width, height);
+        result.WritePixels(dirty, ToByteArray(surface), width * 4, 0);
+        result.AddDirtyRect(dirty);
+        result.Unlock();
+        return result;
+    }
+
+    private static unsafe byte[] ToByteArray(Surface surface, SKColorType colorType = SKColorType.Bgra8888, SKAlphaType alphaType = SKAlphaType.Premul)
+    {
+        int width = surface.Size.X;
+        int height = surface.Size.Y;
+        var imageInfo = new SKImageInfo(width, height, colorType, alphaType, SKColorSpace.CreateSrgb());
+
+        byte[] buffer = new byte[width * height * imageInfo.BytesPerPixel];
+        fixed (void* pointer = buffer)
+        {
+            if (!surface.SkiaSurface.ReadPixels(imageInfo, new IntPtr(pointer), imageInfo.RowBytes, 0, 0))
+            {
+                throw new InvalidOperationException("Could not read surface into buffer");
+            }
+        }
+
+        return buffer;
+    }
+}

src/PixiEditorPrototype/Models/DocumentUpdater.cs

@@ -82,6 +82,11 @@ internal class DocumentUpdater
             case StructureMemberMaskIsVisible_ChangeInfo info:
                 ProcessMaskIsVisible(info);
                 break;
+            case CreateReferenceLayer_ChangeInfo:
+                doc.RaisePropertyChanged(nameof(doc.ReferenceLayer));
+                doc.RaisePropertyChanged(nameof(doc.ReferenceBitmap));
+                doc.RaisePropertyChanged(nameof(doc.ReferenceShape));
+                break;
         }
     }
 

src/PixiEditorPrototype/PixiEditorPrototype.csproj

@@ -8,6 +8,14 @@
     <WarningsAsErrors>Nullable</WarningsAsErrors>
   </PropertyGroup>
 
+  <PropertyGroup Condition=" '$(Configuration)' == 'Debug' ">
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+  </PropertyGroup>
+
+  <PropertyGroup Condition=" '$(Configuration)' == 'Release' ">
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+  </PropertyGroup>
+
   <ItemGroup>
     <PackageReference Include="Dirkster.AvalonDock" Version="4.70.1" />
     <PackageReference Include="Microsoft.Xaml.Behaviors.Wpf" Version="1.1.39" />

src/PixiEditorPrototype/UserControls/Viewport/Viewport.xaml

@@ -32,6 +32,20 @@
                 BorderThickness="1" Background="White" BorderBrush="Black" HorizontalAlignment="Center" VerticalAlignment="Center"
                 DataContext="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=local:Viewport}}">
                 <Grid>
+                    <Image
+                        Width="{Binding Document.Width}" Height="{Binding Document.Height}"/>
+                    <Image
+                        Width="{Binding Document.Width}" Height="{Binding Document.Height}"
+                        Source="{Binding ReferenceBitmap, Mode=OneWay}"
+                        RenderOptions.BitmapScalingMode="{Binding Zoombox.Scale, Converter={StaticResource ScaleToBitmapScalingModeConverter}}">
+                        <Image.RenderTransform>
+                            <TransformGroup>
+                                <TranslateTransform
+                                    X="{Binding ReferenceShape.TopLeft.X}"
+                                    Y="{Binding ReferenceShape.TopLeft.Y}"/>
+                            </TransformGroup>
+                        </Image.RenderTransform>
+                    </Image>
                     <Image 
                         Focusable="True"
                         Width="{Binding Document.Width}" Height="{Binding Document.Height}"

src/PixiEditorPrototype/UserControls/Viewport/Viewport.xaml.cs

@@ -7,6 +7,7 @@ using System.Windows.Data;
 using System.Windows.Input;
 using System.Windows.Media.Imaging;
 using ChunkyImageLib.DataHolders;
+using PixiEditor.ChangeableDocument.Changeables.Interfaces;
 using PixiEditor.Zoombox;
 using PixiEditorPrototype.Models;
 using PixiEditorPrototype.ViewModels;
@@ -38,6 +39,15 @@ internal partial class Viewport : UserControl, INotifyPropertyChanged
     public static readonly DependencyProperty MouseUpCommandProperty =
             DependencyProperty.Register(nameof(MouseUpCommand), typeof(ICommand), typeof(Viewport), new(null));
 
+    public static readonly DependencyProperty ReferenceBitmapProperty =
+        DependencyProperty.Register(nameof(ReferenceBitmap), typeof(BitmapSource), typeof(Viewport));
+    
+    public static readonly DependencyProperty ReferenceLayerProperty =
+        DependencyProperty.Register(nameof(ReferenceLayer), typeof(IReadOnlyReferenceLayer), typeof(Viewport));
+
+    public static readonly DependencyProperty ReferenceShapeProperty =
+        DependencyProperty.Register(nameof(ReferenceShape), typeof(ShapeCorners), typeof(Viewport));
+
     private static readonly DependencyProperty BitmapsProperty =
         DependencyProperty.Register(nameof(Bitmaps), typeof(Dictionary<ChunkResolution, WriteableBitmap>), typeof(Viewport), new(null, OnBitmapsChange));
 
@@ -158,6 +168,24 @@ internal partial class Viewport : UserControl, INotifyPropertyChanged
         }
     }
 
+    public IReadOnlyReferenceLayer? ReferenceLayer
+    {
+        get => (IReadOnlyReferenceLayer?)GetValue(ReferenceLayerProperty);
+        set => SetValue(ReferenceLayerProperty, value);
+    }
+
+    public ShapeCorners ReferenceShape
+    {
+        get => (ShapeCorners)GetValue(ReferenceShapeProperty);
+        set => SetValue(ReferenceLayerProperty, value);
+    }
+
+    public WriteableBitmap? ReferenceBitmap
+    {
+        get => (WriteableBitmap?)GetValue(ReferenceBitmapProperty);
+        set => SetValue(ReferenceBitmapProperty, value);
+    }
+
     public Zoombox Zoombox => zoombox;
 
     public Guid GuidValue { get; } = Guid.NewGuid();
@@ -171,6 +199,21 @@ internal partial class Viewport : UserControl, INotifyPropertyChanged
         binding.Path = new PropertyPath("Document.Bitmaps");
         SetBinding(BitmapsProperty, binding);
 
+        Binding referenceBitmapBinding = new Binding();
+        referenceBitmapBinding.Source = this;
+        referenceBitmapBinding.Path = new PropertyPath("Document.ReferenceBitmap");
+        SetBinding(ReferenceBitmapProperty, referenceBitmapBinding);
+
+        Binding referenceBinding = new Binding();
+        referenceBinding.Source = this;
+        referenceBinding.Path = new PropertyPath("Document.ReferenceLayer");
+        SetBinding(ReferenceLayerProperty, referenceBinding);
+
+        Binding shapeBinding = new Binding();
+        shapeBinding.Source = this;
+        shapeBinding.Path = new PropertyPath("Document.ReferenceShape");
+        SetBinding(ReferenceShapeProperty, shapeBinding);
+
         Loaded += OnLoad;
         Unloaded += OnUnload;
     }

src/PixiEditorPrototype/ViewModels/DocumentViewModel.cs

@@ -12,6 +12,7 @@ using PixiEditor.ChangeableDocument.Changeables.Interfaces;
 using PixiEditor.ChangeableDocument.Enums;
 using PixiEditor.Parser;
 using PixiEditorPrototype.CustomControls.SymmetryOverlay;
+using PixiEditorPrototype.Helpers;
 using PixiEditorPrototype.Models;
 using SkiaSharp;
 
@@ -37,6 +38,7 @@ internal class DocumentViewModel : INotifyPropertyChanged
     public RelayCommand? ToggleLockTransparencyCommand { get; }
     public RelayCommand? ApplyTransformCommand { get; }
     public RelayCommand? PasteImageCommand { get; }
+    public RelayCommand? CreateReferenceLayerCommand { get; }
     public RelayCommand? DragSymmetryCommand { get; }
     public RelayCommand? EndDragSymmetryCommand { get; }
     public RelayCommand? ClipToMemberBelowCommand { get; }
@@ -133,6 +135,11 @@ internal class DocumentViewModel : INotifyPropertyChanged
     public int ResizeWidth { get; set; } = 1024;
     public int ResizeHeight { get; set; } = 1024;
 
+    public IReadOnlyReferenceLayer? ReferenceLayer => Helpers.Tracker.Document.GetReferenceLayer();
+    
+    public BitmapSource? ReferenceBitmap => ReferenceLayer?.Image.ToWriteableBitmap();
+
+    public ShapeCorners ReferenceShape => transformingReferenceLayer ? TransformViewModel.Corners : ReferenceLayer?.Shape ?? default;
 
     private DocumentHelpers Helpers { get; }
 
@@ -149,6 +156,7 @@ internal class DocumentViewModel : INotifyPropertyChanged
     private bool drawingLineBasedPen = false;
     private bool transformingRectangle = false;
     private bool transformingEllipse = false;
+    private bool transformingReferenceLayer = false;
     private bool shiftingLayer = false;
 
     private bool transformingSelectionPath = false;
@@ -188,6 +196,7 @@ internal class DocumentViewModel : INotifyPropertyChanged
         DeleteMaskCommand = new RelayCommand(DeleteMask);
         ToggleLockTransparencyCommand = new RelayCommand(ToggleLockTransparency);
         PasteImageCommand = new RelayCommand(PasteImage);
+        CreateReferenceLayerCommand = new RelayCommand(CreateReferenceLayer);
         ApplyTransformCommand = new RelayCommand(ApplyTransform);
         DragSymmetryCommand = new RelayCommand(DragSymmetry);
         EndDragSymmetryCommand = new RelayCommand(EndDragSymmetry);
@@ -498,6 +507,12 @@ internal class DocumentViewModel : INotifyPropertyChanged
             TransformViewModel.HideTransform();
             Helpers.ActionAccumulator.AddFinishedActions(new EndTransformSelectionPath_Action());
         }
+        else if (transformingReferenceLayer)
+        {
+            transformingReferenceLayer = false;
+            TransformViewModel.HideTransform();
+            Helpers.ActionAccumulator.AddFinishedActions(new EndCreateReferenceLayer_Action());
+        }
         updateableChangeActive = false;
     }
 
@@ -545,8 +560,12 @@ internal class DocumentViewModel : INotifyPropertyChanged
         {
             Helpers.ActionAccumulator.AddActions(new TransformSelectionPath_Action(newCorners));
         }
+        else if (transformingReferenceLayer)
+        {
+            Helpers.ActionAccumulator.AddActions(new CreateReferenceLayer_Action(null, newCorners));
+        }
     }
-
+    
     public void FloodFill(VecI pos, SKColor color)
     {
         var member = FindFirstSelectedMember();
@@ -580,6 +599,34 @@ internal class DocumentViewModel : INotifyPropertyChanged
         TransformViewModel.ShowFreeTransform(corners);
     }
 
+    private void CreateReferenceLayer(object? args)
+    {
+        OpenFileDialog dialog = new();
+        if (dialog.ShowDialog() != true)
+            return;
+
+        var referenceImage = Surface.Load(dialog.FileName);
+
+        double shapeWidth;
+        double shapeHeight;
+
+        if (referenceImage.Size.X > referenceImage.Size.Y)
+        {
+            shapeWidth = Width;
+            shapeHeight = Width / referenceImage.Size.X * referenceImage.Size.Y;
+        }
+        else
+        {
+            shapeWidth = Height / referenceImage.Size.Y * referenceImage.Size.X;
+            shapeHeight = Height;
+        }
+        
+        ShapeCorners corners = new ShapeCorners(new RectD(VecD.Zero, new(shapeWidth, shapeHeight)));
+        Helpers.ActionAccumulator.AddActions(new CreateReferenceLayer_Action(referenceImage, corners));
+        transformingReferenceLayer = true;
+        TransformViewModel.ShowShapeTransform(corners);
+    }
+
     private void ClearSelection(object? param)
     {
         if (updateableChangeActive)

src/PixiEditorPrototype/Views/MainWindow.xaml

@@ -34,6 +34,9 @@
                     <Button Margin="5,0" Command="{Binding ActiveDocument.CreateNewFolderCommand}" Width="80">New Folder</Button>
                     <Button Margin="5,0" Command="{Binding ActiveDocument.DeleteStructureMemberCommand}" Width="80">Delete</Button>
                 </StackPanel>
+                <StackPanel DockPanel.Dock="Top" Orientation="Horizontal" Margin="0,5,0,0">
+                    <Button Margin="5,0" Command="{Binding ActiveDocument.CreateReferenceLayerCommand}" Width="80">Add reference</Button>
+                </StackPanel>
                 <StackPanel DockPanel.Dock="Top" Orientation="Horizontal" Margin="0,5,0,0">
                     <Button Margin="5,0" Command="{Binding ActiveDocument.CreateMaskCommand}" Width="80">Create Mask</Button>
                     <Button Margin="5,0" Command="{Binding ActiveDocument.DeleteMaskCommand}" Width="80">Delete Mask</Button>