SvcSystems.UI.Terminal

An Avalonia terminal control powered by XTerm.NET.

Features

• Terminal emulation, scrollback, selection, search, and caret rendering
• Mouse reporting and Kitty keyboard protocol support
• Sixel graphics
• Clipboard hooks and configurable right-click behavior
• Bindable terminal model and styling hooks
• Desktop sample with shell, scrollback, and selection demos

Install

dotnet add package SvcSystems.UI.Terminal

Quick start

Add the control to a view:

<Window
    xmlns="https://github.com/avaloniaui"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:terminal="using:SvcSystems.UI.Terminal">
    <terminal:TerminalControl Name="TerminalView" />
</Window>

Create a model and connect it to a process or pseudo-terminal. Send process output to Feed and forward every UserInput payload—including keyboard, mouse, and protocol replies—to the process:

var model = new TerminalControlModel();
TerminalView.Model = model;

model.UserInput += (_, e) =>
{
    process.StandardInput.BaseStream.Write(e.Data.Span);
    process.StandardInput.BaseStream.Flush();
};

// For each chunk read from the process:
model.Feed(buffer, bytesRead);

The host owns process and PTY management. TerminalControlModel also supports standalone use, and TerminalOptions can configure the initial size, scrollback, cell metrics, resize reflow, and keyboard protocol.

Interaction

• Selection: drag to select, double-click for a word or expression, and triple-click for a row. Selection extends while dragging outside the viewport.
• Search: call Search(text), then SelectNextSearchResult() or SelectPreviousSearchResult().
• Right-click: choose ContextMenu, CopyOrPaste, or None with RightClickAction.
• Mouse reporting: pointer events go to the terminal application when it enables xterm mouse reporting; otherwise they remain available for selection.
• Kitty keyboard: keys use the protocol only after the application enables it. Disable it with TerminalOptions.KittyKeyboardEnabled = false if needed.

Clipboard reads and terminal-initiated clipboard writes are disabled by default. Hosts handling untrusted terminal output should keep writes disabled unless they have an appropriate user-consent policy.

Styling

Add TerminalTheme to your application styles:

<Application
    xmlns="https://github.com/avaloniaui"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:terminal="using:SvcSystems.UI.Terminal">
    <Application.Styles>
        <terminal:TerminalTheme />
    </Application.Styles>
</Application>

The theme provides the 256-color palette as SvcSystems.UI.TerminalColor0 through SvcSystems.UI.TerminalColor255. Override those resources to customize the palette. Individual controls expose FontFamily, FontSize, CaretBrush, and SelectionBrush. Loading Styles/Colors.axaml with StyleInclude remains supported for compatibility, but TerminalTheme is preferred.

Run the sample

dotnet run --project src/SvcSystems.UI.Terminal.Desktop

The sample includes Shell, Scroll, and Selection tabs. On Windows, the shell prefers a WSL PTY, then falls back to ConPTY and a redirected process. WSL is preferred because ConPTY mediates terminal queries and can change reported capabilities and Unicode widths. A detector run inside Windows Terminal or a ConPTY-backed shell measures that host as well as the control.

Tests

The test project targets .NET 10 and .NET 11. To run the suite on both:

dotnet test --project tests/SvcSystems.UI.Terminal.Tests/SvcSystems.UI.Terminal.Tests.csproj -f net10.0
dotnet test --project tests/SvcSystems.UI.Terminal.Tests/SvcSystems.UI.Terminal.Tests.csproj -f net11.0

The ucs-detect integration tests run the pinned Python detector through a POSIX PTY connected directly to a TerminalControl in an Avalonia Headless window. They check named detector capabilities and Unicode measurements; report-schema checks catch uncovered detector fields. The JSON report, dependency versions, and raw PTY transcript are saved under TestResults/ucs-detect in the test output directory.

The fixture provisions and verifies the pinned dependencies in tests/requirements-ucs-detect.txt. On Linux, Python 3 with venv and pip is required. On Windows, the fixture uses the default Ubuntu WSL distribution and manages its Python environment. Set UCS_DETECT_PYTHON (Linux/macOS) or UCS_DETECT_WSL_PYTHON (Windows) to use an existing environment.

For a focused run, add a test filter, for example:

dotnet test --project tests/SvcSystems.UI.Terminal.Tests/SvcSystems.UI.Terminal.Tests.csproj -f net10.0 -- --filter-class '*UcsDetectIntegrationTests*'

On Windows, the optional UcsDetectConPtyComparisonTests diagnostic compares the direct-PTY baseline with the sample's ConPTY route. Enable it with UCS_DETECT_CONPTY_COMPARE=1; it requires Windows, WSL Ubuntu, and the pinned Python dependencies. The diagnostic is skipped by default.

Benchmarks

Run the Sixel and Kitty image benchmarks in Release mode:

dotnet run -c Release --project benchmarks/SvcSystems.UI.Terminal.Benchmarks -- --filter "*Sixel*" "*Kitty*"

See benchmarks/README.md for results and notes about the headless CPU measurements.