📝 WinUI.DiffViewer

This is a Diff Viewer Control for WinUI 3. It is a reusable class library with a templated control that compares two texts and displays the differences, similar to the JetBrains/IntelliJ Diff Viewer. It supports side-by-side or unified views with line and word highlighting, line number gutters and synchronous scrolling.

The diff engine is a C# port of the IntelliJ algorithm from IntelliJ Community (Apache 2.0 licence). It features Myers O(ND) LCS, line/word/character-based comparison and whitespace ignore policies. And Currently has some MAJOR Bugs.

🚀 Features

Feature	IntelliJ Counterpart
Side-by-Side and Unified mode	SimpleDiffViewer / UnifiedDiffViewer
Green = added, Blue = modified, Gray = deleted	DiffColors (DIFF_INSERTED/MODIFIED/DELETED)
Word/Character highlighting in modified lines	ByWordRt / ByCharRt + InlineHighlighterBuilder
Ignore Differences: None / Trim / Ignore whitespaces	ComparisonPolicy
Highlighting: Lines / Words / Characters / None	HighlightPolicy
Aligned panes (filler lines) + synchronous scrolling	AlignedDiffModel + SyncScrollSupport
Background thread calculation, latest-wins	DiffViewerBase.rediff()
Light/Dark/HighContrast palettes	Editor color schemes
Block splitting: Deletions/Insertions in large modification blocks become separate fragments	ByWordRt.compareAndSplit + LineFragmentSplitter
Boundary correction (changes snap to empty lines/whitespace)	ChunkOptimizer (Line + Word)
Ctrl+Mouse wheel zoom, FontFamily/FontSize switchable live	Editor zoom

🛠️ Usage

<Page xmlns:dv="using:WinUI.DiffViewer.Controls">
    <dv:DiffViewer x:Name="Viewer"
                   ViewMode="SideBySide"
                   IgnorePolicy="Default"
                   HighlightMode="Words" />
</Page>

Viewer.OldText = File.ReadAllText("old.cs");
Viewer.NewText = File.ReadAllText("new.cs");
// All properties are DependencyProperties; every change triggers a diff recalculation.

The engine can also be used without a UI:

using WinUI.DiffViewer.Core;

var result = DiffComputer.Compare(oldText, newText, new DiffOptions {
    Policy = ComparisonPolicy.IgnoreWhitespaces,
    HighlightMode = HighlightMode.Words,
});
foreach (LineFragment f in result.Fragments)
    Console.WriteLine($"{f.Type}: {f}");

Project Structure

src/WinUI.DiffViewer/
  Core/        Diff engine (pure C#, no UI dependency other than the project TFM)
  Model/       Line model: DiffRow, DiffRowBuilder (alignment, highlight spans)
  Controls/    DiffViewer (Templated Control), HighlightableTextBlock, Converters
  Themes/      Generic.xaml (Template + color palettes)
samples/WinUI.DiffViewer.SampleApp/  Gallery sample app (see below)
docs/ARCHITECTURE.md                 Documentation about the App

Sample App

samples/WinUI.DiffViewer.SampleApp is a gallery where you can test the features.

Page	Demonstrates
Overview	All options in one example (View mode, Highlighting, Ignore, Sync-Scroll)
View Modes	ViewMode: SideBySide vs. Unified
Highlighting	HighlightMode: Lines / Words / Characters / None
Whitespace Handling	IgnorePolicy: Default / TrimWhitespaces / IgnoreWhitespaces
Live Editing	Editable panes, DiffComputed event log
Synchronized Scrolling	Documents of different lengths, scroll mapping via change anchors
Large Files	Generated large documents + computation time
Settings	App theme, editor font (Consolas/Cascadia/JetBrains Mono) + font size, version, links

▶️ Build & Start

Requirements: Windows 10/11 and Visual Studio 2022 with the "WinUI application development" workload (or .NET 8 SDK + Windows App SDK 1.5).

dotnet build WinUI.DiffViewer.sln
dotnet run --project samples/WinUI.DiffViewer.SampleApp  (or start via Visual Studio, platform x64.)

Customizing Colors

The line and word backgrounds are set via code-behind (DiffPalette) based on the ActualTheme. Thus, they respect window/element themes and runtime theme changes, and they disable themselves in High Contrast mode (system colors remain readable). You can define your own colors in Application.Resources; they always take precedence:

<Application.Resources>
    <SolidColorBrush x:Key="DiffInsertedRowBrush" Color="#E6FFEC" />
    <SolidColorBrush x:Key="DiffInsertedWordBrush" Color="#ABF2BC" />
    <!-- ebenso: DiffDeletedRowBrush/-WordBrush, DiffModifiedRowBrush/-WordBrush, DiffFillerRowBrush -->
</Application.Resources>

License

Apache License 2.0, see LICENSE. Contains ported code from JetBrains intellij-community.