FujiyNotepad

A lightweight Windows text viewer (WinUI 3) built to open and navigate very large text files that would be slow or impossible to load in a conventional editor.

Instead of reading the whole file into memory, FujiyNotepad reads it on demand in chunks (via the positional RandomAccess API) and draws only the lines currently on screen with a custom text view built from scratch on Win2D (CanvasControl + DirectWrite), not a TextBox. Scrolling, paging, Go To Line, and Find stream directly from disk using a vectorized byte search (ReadOnlySpan<byte>.IndexOf), so memory usage stays roughly constant regardless of file size.

Editions: FujiyNotepad started as a WPF app and was migrated to WinUI 3. The WinUI edition is now the sole, go-forward app; the WPF edition has been retired. Releases are tagged v*.

Download

Grab the latest build from the Releases page. Each release publishes a self-contained Native AOT build for every Windows architecture — each bundles the .NET runtime and the Windows App SDK runtime, so you just unzip and run FujiyNotepad.WinUI.exe with no prerequisites, nothing to install (~22 MB):

Your PC	Download
Most desktops & laptops (Intel/AMD, 64-bit)	FujiyNotepad-<version>-win-x64.zip
Windows on Arm (e.g. Snapdragon, Surface Pro X)	FujiyNotepad-<version>-win-arm64.zip
32-bit Windows	FujiyNotepad-<version>-win-x86.zip

The builds are unsigned, so Windows SmartScreen may warn on first run (More info → Run anyway).

Features

• Open multi-gigabyte text files with near-constant memory usage — a custom view draws only the lines currently on screen, reading each on demand.
• Open a file by dragging it onto the window, from File ▸ Open (Ctrl+O), or via a command-line argument / file association; recently opened files appear under File ▸ Open Recent.
• Reload the open file (F5, or File ▸ Reload) to pick up on-disk changes, keeping the scroll position; when the file changes underneath you, a non-blocking "file changed on disk" hint appears in the status bar so you can reload on demand (handy for growing logs).
• Looks at home on Windows: a Mica backdrop on Windows 11, the open file's name in the title bar, and a text view that follows the system light / dark theme.
• Native-style navigation: mouse wheel, a line-based vertical scrollbar, a horizontal scrollbar, and the keyboard (arrows, PageUp/PageDown, Home/End, Ctrl+Home/Ctrl+End).
• Character-level selection (mouse drag with continuous edge auto-scroll, Shift+click/arrows, double-click to select a word) and copy (Ctrl+C), with a caret and an Ln, Col indicator.
• Background line indexing with progress reporting and cancellation; the scrollbar extent grows as the indexer discovers lines.
• Go To Line (Ctrl+G) and Go To Offset (Ctrl+Shift+G, decimal or 0x hex byte position), plus a non-modal Find bar (Ctrl+F): find next (Enter/F3) and find previous (Shift+Enter/Shift+F3), match case, whole word, regular expressions, a live match count, and all matches highlighted in the viewport (and as ticks on the scrollbar, so you can see where they are across the whole file), with a progress bar and cancel.
• Filter / grep view (Ctrl+Shift+F): show only the lines that contain a term (or match a regular expression), with match case and regex options, so you can sift a huge log down to what matters; clear the filter to return to the full file. While filtering, Edit ▸ Copy Matching Lines and Edit ▸ Save Matching Lines As… export just the matching lines — the GUI equivalent of grep PATTERN file > out.txt (copy is size-capped; save is streamed and uncapped, in UTF-8).
• Persistent highlight rules (View ▸ Highlight Rules…): colour matching text by pattern across the whole file — e.g. ERROR red and WARN amber — with literal or regex rules, per-rule colours (names or hex), and an optional case-sensitive flag. Rules are edited as text, persist across sessions, and apply on top of the filter view. Distinct from Find (which highlights the current search term only).
• Highlight selection occurrences (View ▸ Highlight Selection Occurrences, on by default): selecting a word or any single-line run of text subtly highlights every other occurrence of it in view, so you can spot where a token recurs without starting a search. It stands aside while Find is active (Find wins) and the setting persists.
• Bookmarks: toggle a bookmark on the caret line (Ctrl+F2) and jump to the next / previous one (F2 / Shift+F2, wrapping around), to flag points of interest in a large file. Bookmarked lines show a dot in the line-number gutter (View ▸ Line Numbers) and a tick on the scrollbar so you can see where they are at a glance; Edit ▸ Clear All Bookmarks removes them.
• Quick clipboard / file actions: Edit ▸ Copy with Line Numbers (Ctrl+Shift+C) copies the selected lines (or the caret line) each prefixed with its line number; File ▸ Copy File Path puts the open file's full path on the clipboard; File ▸ Reveal in Explorer opens its folder with the file selected.
• Show whitespace (View ▸ Show Whitespace): overlay faint markers for spaces (dots), tabs (arrows), line endings (a return mark, distinguishing LF from CRLF) and other control characters (boxes), with trailing whitespace emphasized, for inspecting log/data files where exact spacing matters.
• Character encoding: auto-detects UTF-8, UTF-16 (LE/BE) and UTF-32 (LE/BE) from the byte-order mark or a heuristic, with Windows-1252 (ANSI) as a fallback, so Windows logs and exports don't render as mojibake. The Encoding menu shows the detection and lets you override it.
• Configurable tab width (2 / 4 / 8) and wide / CJK glyph handling (East Asian wide and fullwidth characters occupy two columns).
• Zoom (Ctrl++ / Ctrl+- / Ctrl+0, or Ctrl+mouse wheel) with the current percentage in the status bar, an optional line-number gutter (View ▸ Line Numbers), a choice of monospace fonts (View ▸ Font), a theme override (View ▸ Theme: System / Light / Dark), and the file's total line and character counts shown in the status bar (alongside the encoding, the line-ending type — LF / CRLF / Mixed — and the Ln, Col caret position).
• File ▸ Open Sample generates a large (~10M line) file — with a short feature-demo header — to showcase performance.

Requirements

• Windows 10 (version 1809 / build 17763) or Windows 11 — x64, Arm64, or x86.
• Released builds need nothing installed (self-contained Native AOT).
• To build from source: the .NET 10 SDK. Running an unpackaged dev build also needs the Windows App SDK runtime (already on most dev machines); released self-contained builds bundle it, so they need nothing.

Build & run

# From the repository root
dotnet build src/FujiyNotepad.slnx -c Release
dotnet run --project src/FujiyNotepad.WinUI -c Release

Or open src/FujiyNotepad.slnx in Visual Studio 2022 (17.13+, for the .slnx solution format) and press F5.

The app is unpackaged (WindowsPackageType=None), so the produced .exe runs directly. The release build additionally uses Native AOT (PublishAot=true); building AOT locally requires the Desktop development with C++ workload (the CI runner already has it).

Release

A v* tag triggers release.yml, which publishes a self-contained Native AOT build for each architecture (win-x64, win-arm64, win-x86) — native code with the .NET and Windows App SDK runtimes bundled — then zips it and attaches it to a GitHub Release. The same workflow has a manual workflow_dispatch dry-run that produces the artifacts without creating a release.

Project layout

Path	Description
src/FujiyNotepad.Core	UI-agnostic engine: FileByteSource (positional RandomAccess I/O), TextSearcher (chunked, vectorized byte search), LineIndexer (background line-offset index), LineProvider (decode a line on demand), LineColumns (tab/column + wide-glyph mapping).
src/FujiyNotepad.Core.Tests	xUnit tests for the engine (run headless, no UI).
src/FujiyNotepad.Presentation	Framework-independent text-view logic: scroll/caret/selection, hit-testing, word selection, copy, and the per-line render model. No Win2D/WinUI dependency, so it unit-tests on a normal test host.
src/FujiyNotepad.Presentation.Tests	xUnit tests for the view logic and render model.
src/FujiyNotepad.WinUI	The WinUI 3 app: Controls/TextCanvas.cs (Win2D surface that paints the engine's render model and forwards input) and MainWindow (menus, scrollbars, status bar, Go To Line, Find bar, Filter bar, highlight rules).
src/FujiyNotepad.Benchmarks	BenchmarkDotNet micro-benchmarks for the engine's hot paths (manual; see the project's README).

Architecture

WinUI has no text control that virtualizes over a file — its virtualization seam lives only in the items controls — so the view is a custom text surface drawn from scratch with Win2D (CanvasControl + DirectWrite), not a TextBox/ListView. TextCanvas is a thin Win2D shell: it owns the CanvasControl, font metrics, focus, the clipboard, and the caret-blink/auto-scroll timers, maps pointer/keyboard input to the TextLayoutEngine, and paints its per-line render model. All scroll/caret/ selection math lives in FujiyNotepad.Presentation, and the on-disk engine lives in FujiyNotepad.Core; both are free of any Win2D/WinUI/WinRT dependency, so they're covered by xUnit tests that run on a normal .NET host. Windows App SDK UI can't be driven on headless CI, so interaction and visual details (selection feel, scrolling, rendering crispness) are best confirmed hands-on on a real desktop.

Diagnostics

If the app ever closes unexpectedly, it appends the exception (type, message, and stack trace) to %LOCALAPPDATA%\FujiyNotepad\crash.log — the same folder as settings.json. Attaching that file to a bug report makes a Native AOT crash much easier to diagnose. (Logging is best-effort and never blocks or changes shutdown; the app still terminates as usual.)

Contributing

Bug reports and pull requests are welcome — see CONTRIBUTING.md for the build/test workflow and conventions, and CHANGELOG.md for release history.

License

See LICENSE.