Sixel image support now that Terminal has it

[kzu]

Windows Terminal finally has support for rendering images!

Would be awesome to have them via Spectre too (CanvasImage or otherwise).

microsoft/terminal#448

[kzu]

I can successfully detect Sixel support with the following:

Console.Write("\x1B[c");

// Wait for awhile to let the terminal respond
Thread.Sleep(100);
var sb = new StringBuilder();

// Read all input available, non-blocking
while (Console.KeyAvailable)
{
    var key = Console.ReadKey(true);
    sb.Append(key.KeyChar);
}
var response = sb.ToString();
// Quick-n-dirty way to detect sixel capability
var split = response.Split(';');

// 4 is the sixel capability
if (!split.Contains("4"))
{
    AnsiConsole.MarkupLine("[red]Your terminal does not support sixel graphics.[/]");
    return -1;
}

From this, GitHub Copilot says:

Console capabilities detection in Spectre.Console is handled mainly through the Capabilities class and some platform-specific logic, especially around ANSI/VT sequences.

How does it work?

• Capabilities Storage: The Capabilities class (see src/Spectre.Console/Capabilities.cs) holds information about what the console supports: ANSI, Unicode, links, alternate buffer, interactivity, etc.
• Detection Mechanism: Detection logic is implemented in platform-specific ways. For ANSI/VT support, the logic is in AnsiDetector:
  • On Windows, it checks environment variables (like ConEmuANSI) and tries to enable ANSI mode with native APIs.
  • On Unix-like systems, it inspects the TERM environment variable for known patterns.
• Interactivity: As of v0.45, detection of interactivity uses Console.IsInputRedirected rather than Environment.UserInteractive.

How to extend for Sixel detection

The current Spectre.Console implementation does not probe for Sixel (a raster graphics protocol) support. Your sample code sends the ANSI device attributes request (ESC [ c) and parses the terminal's response to see if Sixel is supported.

Where to hook in?

• You would add a similar runtime probe in the detection sequence. The most logical place is to extend the Capabilities class and the logic where ANSI/terminal features are detected.
• You might create a new property in Capabilities (e.g., public bool Sixel { get; set; }).
• The detection logic would run your Sixel probe at startup/initialization, similar to how ANSI is detected.

Example sketch

Add to Capabilities:

public bool Sixel { get; set; }

Extend detection (pseudo-code):

// In your detection logic (maybe a new method in Capabilities or a helper class)
public static bool DetectSixelSupport()
{
    // Write ESC [ c
    Console.Write("\x1B[c");
    Thread.Sleep(100);
    var sb = new StringBuilder();
    while (Console.KeyAvailable)
    {
        var key = Console.ReadKey(true);
        sb.Append(key.KeyChar);
    }
    var response = sb.ToString();
    var split = response.Split(';');
    return split.Contains("4"); // 4 = Sixel support
}

Then, set the property during initialization:

capabilities.Sixel = DetectSixelSupport();

Integration

• The actual place to insert this will depend on whether you want to make Sixel detection conditional, configurable, or always-on.
• You'd likely want to make this detection asynchronous or at least optional, since it involves waiting for terminal I/O.

---

Summary:
Spectre.Console detects features by inspecting environment variables, checking for ANSI/VT support, and storing this in the Capabilities class. To add Sixel detection, you would add a new property to Capabilities and implement your probe in the startup/initialization logic that populates Capabilities, similar to your sample code.

[phil-scott-78]

there is a pull request from last that needs some love that adds it - #1679

I think the scope of what the support should be got everyone moving in different directions and it didn't go much further. Neat idea though, but its either a nice little way to display images or it could be total rewrite of some core stuff like progress bars and status bars

[kzu]

Ah, I see. Well, without ImageSharp, this is (mostly?) a dead-end. So I'll just roll my own. Thanks for the pointer!

#1679 (comment)