jamescrosswell · Oct 14, 2026 · Oct 13, 2026
diff --git a/.tui/TuiCode.workspaces.json b/.tui/TuiCode.workspaces.json
@@ -1,4 +1,9 @@
 [
+  {
+    "Folder": "/Users/jamescrosswell/code/TuiCode/about-kitty",
+    "Files": [],
+    "Active": null
+  },
   {
     "Folder": "/Users/jamescrosswell/code/TuiCode/tabstrip-no-default-key",
     "Files": [

diff --git a/AGENTS.md b/AGENTS.md
@@ -237,13 +237,14 @@ What follows is how TuiCode implements it today.
 
 ## About dialog (#107)
 
-- `tui` opens `AboutView`. If the terminal supports sixel (WezTerm, iTerm2, tmux 3.6, Windows Terminal, foot…) it shows the artwork as an image. Otherwise (kitty, Ghostty, Terminal.app — TG 2.1.0 has no kitty graphics) it shows ASCII art.
+- `tui` opens `AboutView`, which draws the artwork with TG's `ImageView` (#537): through kitty graphics in kitty and Ghostty, through sixel in WezTerm, iTerm2, tmux 3.6, Windows Terminal, foot…, and as ASCII art where neither works (Alacritty, Terminal.app). We don't use `ImageView`'s coloured-cell fallback: at the dialog's size it doesn't read as the logo. F12 Diagnostics' **Image protocol** row says which one About uses.
+- `ImageProtocols.Choose` decides. Kitty graphics comes from TG's own detection (`IDriver.KittyGraphicsSupport`, which goes by `KITTY_WINDOW_ID` / `TERM_PROGRAM`), except inside tmux (`TMUX`), which needs passthrough for it. Sixel comes from our probe. `ImageProtocols.Configure` then hands the driver our answer and cell size (`SetSixelSupport`, `SetKittyGraphicsSupport`) on every open, so TG's own sixel detection, which gets both wrong below, doesn't decide; in tmux it also turns off the kitty graphics TG detected from a leaked `KITTY_WINDOW_ID`.
 - `SixelProbe.Detect` sends DA1 once at startup (`WorkbenchHost` ctor), so the dialog knows up front and shows a spinner, not ASCII art that gets replaced. `SixelProbe.MeasureCell` runs each time About opens, because the cell's pixel size changes when the window moves between a Retina and a non-Retina screen. We don't use TG's `SixelSupportDetector`: it asks `CSI 16 t` first and iTerm2 never answers, which costs TG's 1 s abandon timeout, and its fallback (window pixels ÷ cells) counts the title bar and margins. `MeasureCell` sends iTerm2's `OSC 1337 ; ReportCellSize` and `CSI 16 t` together and takes the first answer. `Detect` also parses tmux's DA1 reply (`…;4c`), which TG's check misses.
 - iTerm2 reports sizes in points everywhere, its `CSI 14 t` reply included. Only `ReportCellSize` carries the scale (`2.0` on Retina), so `ParseIterm2CellSize` multiplies by it (clamped to 1–4; absent in older iTerm2s, meaning 1). Sixels are drawn in device pixels, so ignoring it drew the About image at a quarter of its area (#333).
 - F12 Diagnostics runs `MeasureCell` too each time it opens and shows the size with the reply it came from (`CellMeasurement.Source`), or that none came and 10 × 20 was assumed (#335).
-- The cell size has to be exact: iTerm2 blanks every row an image touches, so an image that ends mid-row leaves a dark band (`AboutImage.Fit` rounds down to whole rows and `Cover` trims the top/bottom to match).
-- Encoding runs in the background and is cached per pixel size, so reopening shows the image immediately.
-- TG re-emits queued sixels on every output write and only rewrites cells whose contents changed, so `AboutView.Dispose` dequeues its sixel and sets `ClearScreenNextIteration`. Otherwise the image stays on screen after close.
+- The cell size has to be exact: iTerm2 blanks every row an image touches, so an image that ends mid-row leaves a dark band. `AboutImage.Fit` rounds down to whole rows and `Cover` trims the top/bottom to match, so `ImageView` gets an image exactly the size of its viewport and draws it unscaled. The driver takes a whole-pixel cell size, so `Configure` rounds ours.
+- The host keeps one `ImageView` (`AboutView.CreateImage`) across opens, since it caches its sixel encoding, and the scaled image is cached per pixel size, so reopening shows the image straight away. `AboutView.Dispose` takes it out before disposing the rest. Its pan and zoom keys and mouse bindings are off: About is a picture, not a viewer.
+- TG deletes a raster image once its view leaves the hierarchy, but `AboutView.Dispose` still sets `ClearScreenNextIteration` after drawing one, for terminals that keep a sixel until its cells are written again.
 - The artwork is `assets/about.png`, baked into the embedded `About/about.rgb.z` (raw RGB, zlib) by `dotnet run scripts/update-about-image.cs`. We have no image decoder at runtime and don't want one in the AOT binary.
 
 ## File icons (#119)

diff --git a/src/TuiCode.Workbench/About/AboutView.cs b/src/TuiCode.Workbench/About/AboutView.cs
@@ -1,6 +1,4 @@
-using Point = System.Drawing.Point;
 using Size = System.Drawing.Size;
-using Terminal.Gui.Drivers;
 using TuiCode.Abstractions;
 using TuiCode.Workbench.Services;
 
@@ -31,20 +29,21 @@ public sealed class AboutView : Window
     private const int ChromeHeight = 8;
 
     private readonly AboutArt _art;
-    private static readonly System.Collections.Concurrent.ConcurrentDictionary<Size, string> EncodedImages = new();
+    private readonly ImageView _image;
+    private static readonly System.Collections.Concurrent.ConcurrentDictionary<Size, Color[,]> ScaledImages = new();
 
-    private IApplication? _app;
-    private SixelToRender? _sixel;
     private bool _disposed;
 
     public IKeybindingService Scope => _scopeKeybindings;
 
     internal bool IsLoading => _art.Mode == ArtMode.Loading;
     internal bool ShowsAsciiArt => _art.Mode == ArtMode.Ascii;
+    internal bool ShowsImage => _art.Mode == ArtMode.Image;
 
     public event EventHandler? Closed;
 
-    public AboutView(string version)
+    /// <param name="image">Kept by the caller across opens, so it doesn't encode the image again.</param>
+    public AboutView(string version, ImageView image)
     {
         Title = "About";
         BorderStyle = LineStyle.Single;
@@ -62,6 +61,12 @@ public AboutView(string version)
             Height = Art.Length,
         };
 
+        _image = image;
+        _image.X = 1;
+        _image.Y = 1;
+        _image.Width = Dim.Fill(1);
+        _image.Visible = false;
+
         var details = new Label
         {
             X = Pos.Center(),
@@ -77,7 +82,7 @@ public AboutView(string version)
             Text = "Esc · Enter  close",
         };
 
-        Add(art, details, footer);
+        Add(art, _image, details, footer);
 
         _scopeCommands = new CommandService();
         _scopeKeybindings = new KeybindingService(_scopeCommands);
@@ -86,60 +91,63 @@ public AboutView(string version)
         _scopeKeybindings.Bind("Enter", CommandIds.AboutClose);
     }
 
-    /// <summary>
-    /// Shows the artwork as a sixel image if <paramref name="support"/> allows, else the ASCII art. Null means
-    /// detection is still running. Call once the view is added.
-    /// </summary>
-    internal void Present(SixelSupport? support)
+    /// <summary>An <see cref="ImageView"/> for <see cref="AboutView"/>: a picture, without pan and zoom.</summary>
+    public static ImageView CreateImage()
     {
-        if (_disposed || App is not { Driver: { } driver } app) return;
-
-        if (support is null)
+        var image = new ImageView
         {
-            StartLoading(app);
-            return;
-        }
+            CanFocus = false,
+            UseBackgroundRendering = true,
+            MaxSixelPaletteColors = 256,
+        };
+        image.MouseBindings.Clear();
+        return image;
+    }
 
-        if (!support.IsSupported)
-        {
-            _art.Mode = ArtMode.Ascii;
-            _art.SetNeedsDraw();
-            return;
-        }
+    internal void ShowAsciiArt()
+    {
+        _image.Visible = false;
+        _art.Mode = ArtMode.Ascii;
+        _art.SetNeedsDraw();
+    }
+
+    /// <summary>Shows the artwork through whichever protocol the driver has been given, <paramref name="cellPixels"/> to a cell.</summary>
+    internal void ShowImage(Size cellPixels)
+    {
+        if (_disposed || App is not { } app) return;
 
         var columns = Art.Max(line => line.Length);
-        var (pixels, rows) = AboutImage.Fit(AboutImage.ReadSize(), support.CellPixels, columns);
+        var (pixels, rows) = AboutImage.Fit(AboutImage.ReadSize(), cellPixels, columns);
         _art.Height = rows;
+        _image.Height = rows;
         Height = rows + ChromeHeight;
 
-        if (EncodedImages.TryGetValue(pixels, out var cached))
+        if (ScaledImages.TryGetValue(pixels, out var cached))
         {
-            ShowSixel(app, driver, cached);
+            Show(cached);
             return;
         }
 
-        StartLoading(app);
+        ShowLoading();
         Task.Run(() =>
         {
-            var data = EncodedImages.GetOrAdd(pixels, size => new SixelEncoder().EncodeSixel(AboutImage.Cover(AboutImage.Load(), size)));
-            app.Invoke(() => ShowSixel(app, driver, data));
+            var image = ScaledImages.GetOrAdd(pixels, size => AboutImage.Cover(AboutImage.Load(), size));
+            app.Invoke(() => Show(image));
         });
     }
 
-    private void ShowSixel(IApplication app, IDriver driver, string data)
+    private void Show(Color[,] image)
     {
         if (_disposed) return;
-        _app = app;
-        _sixel = new SixelToRender { Id = "about", SixelData = data };
-        _art.Sixel = _sixel;
+        if (!ReferenceEquals(_image.Image, image)) _image.Image = image;
+        _image.Visible = true;
         _art.Mode = ArtMode.Image;
-        driver.GetOutput().GetSixels().Enqueue(_sixel);
         _art.SetNeedsDraw();
     }
 
-    private void StartLoading(IApplication app)
+    internal void ShowLoading()
     {
-        if (_art.Mode == ArtMode.Loading) return;
+        if (_disposed || App is not { } app || _art.Mode == ArtMode.Loading) return;
         _art.Mode = ArtMode.Loading;
         _art.SetNeedsDraw();
         app.AddTimeout(TimeSpan.FromMilliseconds(80), () =>
@@ -153,14 +161,11 @@ private void StartLoading(IApplication app)
 
     protected override void Dispose(bool disposing)
     {
-        if (disposing && !_disposed && _sixel is not null && _app?.Driver is { } driver)
+        if (disposing && !_disposed)
         {
-            var sixels = driver.GetOutput().GetSixels();
-            var others = sixels.Where(s => !ReferenceEquals(s, _sixel)).ToList();
-            sixels.Clear();
-            foreach (var other in others) sixels.Enqueue(other);
-            // TG only rewrites cells whose contents changed, which would leave the image on screen.
-            _app.ClearScreenNextIteration = true;
+            Remove(_image);
+            // Some terminals keep a sixel until the cells under it are written again.
+            if (_art.Mode == ArtMode.Image && App is { } app) app.ClearScreenNextIteration = true;
         }
         _disposed = true;
         base.Dispose(disposing);
@@ -175,15 +180,13 @@ private sealed class AboutArt : View
 
         public ArtMode Mode { get; set; }
         public int SpinnerFrame { get; set; }
-        public SixelToRender? Sixel { get; set; }
 
         protected override bool OnDrawingContent(DrawContext? context)
         {
             SetAttribute(GetAttributeForRole(VisualRole.Normal) with { Foreground = Green });
             switch (Mode)
             {
                 case ArtMode.Image:
-                    Sixel!.ScreenPosition = ViewportToScreen(Point.Empty);
                     break;
                 case ArtMode.Loading:
                     Move(Viewport.Width / 2, Viewport.Height / 2);

diff --git a/src/TuiCode.Workbench/About/ImageProtocols.cs b/src/TuiCode.Workbench/About/ImageProtocols.cs
@@ -0,0 +1,44 @@
+using Terminal.Gui.Drivers;
+using Size = System.Drawing.Size;
+using SizeF = System.Drawing.SizeF;
+
+namespace TuiCode.Workbench.About;
+
+internal enum ImageProtocol { None, Sixel, Kitty }
+
+internal static class ImageProtocols
+{
+    /// <summary>Kitty graphics where Terminal.Gui found it outside tmux, else sixel where our probe found it. Null while that's unknown.</summary>
+    public static ImageProtocol? Choose(bool kittyDetected, bool inTmux, bool? sixel) =>
+        kittyDetected && !inTmux ? ImageProtocol.Kitty
+        : sixel switch
+        {
+            true => ImageProtocol.Sixel,
+            false => ImageProtocol.None,
+            null => null,
+        };
+
+    public static string Describe(ImageProtocol? protocol) => protocol switch
+    {
+        ImageProtocol.Kitty => "kitty graphics",
+        ImageProtocol.Sixel => "sixel",
+        ImageProtocol.None => "none (ASCII art)",
+        _ => "asking the terminal…",
+    };
+
+    /// <summary>Tells the driver what our probe found, so Terminal.Gui's own detection doesn't decide. Returns the cell size it was given.</summary>
+    public static Size Configure(IDriver driver, ImageProtocol protocol, SizeF cellPixels)
+    {
+        var cell = new Size((int)Math.Round(cellPixels.Width), (int)Math.Round(cellPixels.Height));
+        if (protocol == ImageProtocol.Kitty)
+        {
+            driver.SetKittyGraphicsSupport(new KittyGraphicsSupportResult { IsSupported = true, Resolution = cell });
+            return cell;
+        }
+
+        if (driver.KittyGraphicsSupport is { IsSupported: true })
+            driver.SetKittyGraphicsSupport(new KittyGraphicsSupportResult { IsSupported = false, Resolution = cell });
+        driver.SetSixelSupport(new SixelSupportResult { IsSupported = protocol == ImageProtocol.Sixel, Resolution = cell });
+        return cell;
+    }
+}
diff --git a/src/TuiCode.Workbench/About/SixelProbe.cs b/src/TuiCode.Workbench/About/SixelProbe.cs
@@ -5,11 +5,6 @@
 
 namespace TuiCode.Workbench.About;
 
-internal sealed record SixelSupport(bool IsSupported, SizeF CellPixels)
-{
-    public static readonly SixelSupport Unsupported = new(false, SizeF.Empty);
-}
-
 internal enum CellSizeSource { Iterm2Report, CellResolutionReply, Assumed }
 
 internal sealed record CellMeasurement(SizeF Pixels, CellSizeSource Source, float Scale = 1);

diff --git a/src/TuiCode.Workbench/Diagnostics/DiagnosticsView.cs b/src/TuiCode.Workbench/Diagnostics/DiagnosticsView.cs
@@ -19,13 +19,14 @@ public sealed class DiagnosticsView : Window
     private readonly Label _keyRune;
     private readonly Label _cursorColour;
     private readonly Label _cellSize;
+    private readonly Label _imageProtocol;
     private readonly string? _askedCursorColour;
 
     public IKeybindingService Scope => _scopeKeybindings;
 
     public event EventHandler? Closed;
 
-    public DiagnosticsView(string driverName, string kittyNegotiationStatus, string? cursorColour = null)
+    public DiagnosticsView(string driverName, string kittyNegotiationStatus, string? cursorColour = null, string imageProtocol = "")
     {
         _askedCursorColour = cursorColour;
         Title = "Diagnostics";
@@ -39,7 +40,8 @@ public DiagnosticsView(string driverName, string kittyNegotiationStatus, string?
         var kittyStatusText = string.Join("\n", kittyStatusLines);
         var cursorColourY = 2 + kittyStatusLines.Length;
         var cellSizeY = cursorColourY + 1;
-        var keyHeadingY = cellSizeY + 2;
+        var imageProtocolY = cellSizeY + 1;
+        var keyHeadingY = imageProtocolY + 2;
         var nameY = keyHeadingY + 1;
         var hintY = nameY + 6;
         Height = hintY + 6;
@@ -86,6 +88,15 @@ public DiagnosticsView(string driverName, string kittyNegotiationStatus, string?
             Text = "asking the terminal…",
         };
 
+        var imageProtocolHeading = Heading("Image protocol", imageProtocolY);
+        _imageProtocol = new Label
+        {
+            X = FieldX,
+            Y = imageProtocolY,
+            Width = GetFieldWidth(),
+            Text = imageProtocol,
+        };
+
         var keyHeading = Heading("Last key", keyHeadingY);
         var nameLabel = Heading("  Name", nameY);
         var hexLabel = Heading("  Hex", nameY + 1);
@@ -114,6 +125,7 @@ public DiagnosticsView(string driverName, string kittyNegotiationStatus, string?
         Add(driverHeading, driverNameLabel, kittyHeading, kittyStatusLabel,
             cursorColourHeading, _cursorColour,
             cellSizeHeading, _cellSize,
+            imageProtocolHeading, _imageProtocol,
             keyHeading, nameLabel, hexLabel, baseLabel, runeLabel,
             _keyName, _keyHex, _keyBase, _keyRune,
             hint, footer);
@@ -178,6 +190,8 @@ public void ShowTerminalCursorColour(string? reported)
 
     public string CellSizeText => _cellSize.Text;
 
+    public string ImageProtocolText => _imageProtocol.Text;
+
     internal void ShowCellSize(CellMeasurement cell) => _cellSize.Text = DescribeCellSize(cell);
 
     private static string DescribeCellSize(CellMeasurement cell)

diff --git a/src/TuiCode.Workbench/WorkbenchHost.cs b/src/TuiCode.Workbench/WorkbenchHost.cs
@@ -99,6 +99,7 @@ public sealed class WorkbenchHost : IDisposable
     private DiagnosticsView? _activeDiagnostics;
     private string? _cursorColour;
     private AboutView? _activeAbout;
+    private readonly ImageView _aboutImage = AboutView.CreateImage();
     private DocumentInfoView? _activeDocumentInfo;
     private BlameView? _activeBlame;
     private bool? _sixelSupported;
@@ -2210,7 +2211,7 @@ private void OpenAbout()
     {
         if (_activeAbout is not null) return;
 
-        var view = new AboutView(AppVersion.Current);
+        var view = new AboutView(AppVersion.Current, _aboutImage);
         view.Closed += (_, _) => CloseAbout(view);
         _activeAbout = view;
         _workbench.Add(view);
@@ -2222,20 +2223,32 @@ private void OpenAbout()
 
     private void PresentAbout(AboutView view)
     {
-        if (_sixelSupported is not true || _app.Driver is not { } driver)
+        if (_app.Driver is not { } driver || AboutImageProtocol() is not { } protocol)
         {
-            view.Present(_sixelSupported is null ? null : SixelSupport.Unsupported);
+            view.ShowLoading();
+            return;
+        }
+
+        if (protocol == ImageProtocol.None)
+        {
+            view.ShowAsciiArt();
             return;
         }
 
-        view.Present(null);
+        view.ShowLoading();
         // Measured on every open: the window may have moved to a screen with another scale since the last one.
         SixelProbe.MeasureCell(driver, cell => _app.Invoke(() =>
         {
-            if (ReferenceEquals(_activeAbout, view)) view.Present(new SixelSupport(true, cell.Pixels));
+            if (ReferenceEquals(_activeAbout, view)) view.ShowImage(ImageProtocols.Configure(driver, protocol, cell.Pixels));
         }));
     }
 
+    internal ImageProtocol? AboutImageProtocol() =>
+        _app.Driver is { } driver
+            ? ImageProtocols.Choose(driver.KittyGraphicsSupport is { IsSupported: true },
+                !string.IsNullOrEmpty(_environment.GetEnvironmentVariable("TMUX")), _sixelSupported)
+            : ImageProtocol.None;
+
     private void CloseAbout(AboutView view)
     {
         if (!ReferenceEquals(_activeAbout, view)) return;
@@ -3557,7 +3570,7 @@ private void OpenDiagnostics()
 
         var driverName = _app.Driver?.GetName() ?? "Unknown";
         var kittyNegotiationStatus = GetKittyNegotiationStatus();
-        var view = new DiagnosticsView(driverName, kittyNegotiationStatus, _cursorColour);
+        var view = new DiagnosticsView(driverName, kittyNegotiationStatus, _cursorColour, ImageProtocols.Describe(AboutImageProtocol()));
         view.Closed += (_, _) => CloseDiagnostics(view);
         _activeDiagnostics = view;
         _workbench.Add(view);
@@ -3645,6 +3658,7 @@ public void Dispose()
         _find.Dispose();
         _terminalCursors.Dispose();
         _workbench.Dispose();
+        _aboutImage.Dispose();
         _app.Dispose();
         // Tell WezTerm and kitty to stop remapping keys; matches the startup activation.
         // Emitted post-Dispose so it reaches the live terminal after TG restores it.