KMark — Native WYSIWYG Markdown & Text Editor for KDE Plasma

KMark is a fast, native WYSIWYG Markdown and plain-text editor for Linux & KDE Plasma, combining the immediate typographic editing experience of MDNote with the native desktop conventions, menus, shortcuts, and Breeze styling of KDE Kate / KWrite.

KMark uses a Single-Buffer Projected Editor architecture written in safe Rust (unsafe_code = "forbid") across its core crates, paired with a thin native C++20 Qt6 / KDE Frameworks 6 (KXmlGuiWindow + QPainter) shell.

Above: Default System (KDE Breeze) preset with slanted heading bars · Below: Built-in Classic ("Klassisch") preset with warm paper background, serif typography, and clean book-style headings:

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Highlights

• Four Seamless View Modes over a Single UTF-8 Rope Buffer (zero lossy round-trip conversions):
  1. Formatted (WYSIWYG) — Type directly inside the typeset document; Markdown markers (**, *, #, […](…)) stay hidden while slanted left-margin H1–H6 bars indicate heading levels.
  2. Live Preview — Full document formatted, while the active block under the caret reveals its underlying Markdown syntax.
  3. Markdown Source — Monospace syntax highlighting with optional line numbers (F11).
  4. Plain Text (TXT) — Distraction-free plain-text editor mode (activated automatically for .txt files).
• True 2D GFM Table Grid with Contextual Table Toolbar & Smart Column Balancing:
  • Direct in-cell editing mapped to exact byte ranges, min-content-aware column sizing (preventing narrow single-word columns from squeezing mid-word next to wide neighbors), per-column alignment (Left, Center, Right), Tab / Shift+Tab cell navigation, automatic row creation at table end, and row/column insertion & deletion.
  • Contextual Table Toolbar: Moving the caret inside any table automatically reveals inline row, column, and column-alignment toolbar actions (Insert Row Above/Below, Delete Row, Insert Column Left/Right, Delete Column, Align Left/Center/Right).
• Unified Settings Dialog, Appearance Presets & Persistent State:
  • Configure body & monospace fonts, font size, line spacing, max column width, Heading Indicators (Slanted Bars, # Hash, or None), editor view toggles, and 8 custom editor colors in a unified KDE Settings Dialog (Settings -> Configure KMark…, Ctrl+Shift+,) with a live WYSIWYG preview card.
  • Ships with 6 curated Appearance Presets (System (KDE Breeze), Modern, Classic, Calm, Dark (Night Studio), Technical) plus custom user-saved presets selectable directly from Settings -> Appearance Presets.
  • Automatically persists appearance, editor options, recent files, last folder root, and window/dock state across restarts.
• Clickable Code Block Language & Callout Type Selectors + Interactive Task Lists:
  • Every fenced code block displays a clickable language badge (rust ▾ / Code ▾) in the top-right corner during Formatted and Live Preview modes (also accessible via Format -> Code Block Language… or Ctrl+Alt+L).
  • Every Callout / GFM Alert ([!NOTE], [!TIP], [!IMPORTANT], [!WARNING], [!CAUTION]) displays a clickable top-right type badge (Note ▾ / Hinweis ▾) to switch Callout types in-place or convert back to a plain blockquote.
  • Task list checkboxes (- [ ] / - [x]) toggle directly on click.
• Inline Images with Captions, Relative Sizing & Context Menu:
  • Drag & drop image files (.png, .jpg, .svg, .webp, .gif, .avif) from Dolphin or paste screenshots directly from the clipboard to insert clean relative paths and render local images inline.
  • Supports centered italic image captions (![alt](img.png "Caption")) and relative percentage widths (![alt](img.png "Caption"){width=50%}), editable via a right-click Image Context Menu (Add/Edit Caption, Replace Image, Size: Automatic / 25%–100% / Custom %).
• Armed Formatting & Smart Structural Editing:
  • Pressing Ctrl+B or Ctrl+I outside a word arms the style without littering empty **** markers into the buffer until you actually type.
  • Enter continues bullet lists, numbered lists (1. -> 2.), task lists, and blockquotes — and exits cleanly on a second Enter on an empty item.
• Native KDE Plasma Shell (English & Deutsch):
  • Integrates with KDE Frameworks 6 (KXmlGuiWindow, Breeze Light & Dark QPalette tracking, standard KDE shortcuts) and automatically detects the system locale (KLocalizedString / LANGUAGE / LANG), currently shipping built-in English and German UI strings (I18n.h).
  • Built-in Markdown Quick Reference (F1) and Markdown Complete Reference (Shift+F1).
  • Persistent Open Recent (File -> Open Recent) menu, multi-tab crash recovery (~/.local/state/kmark/recovery/), dockable Outline (F9) & Folder Tree (F7) with parent/home navigation and a PhpStorm-style Select Opened File action button, Kate-style bottom Find/Replace bar (Ctrl+F / Ctrl+R, RegEx), HTML5 export, and PDF/CUPS print preview.
• Fast Virtualized Editing on Large Documents:
  • Persistent Copy-on-Write B-tree Rope (O(log N)), exact diff-window incremental block & outline updates, persistent BlockHeightCache scroll virtualization, single-pass QTextLayout run shaping, and cached cursor-blink frames (cargo run --release -p kmark-cli -- bench headless FallbackMeasurer, 25-run medians: ~0.35 ms edit+layout / ~0.26 ms scroll frame at 6,000 lines; ~0.60 ms edit+layout / ~0.42 ms scroll frame / ~1.3 ms cold first frame at 60,000 lines; ~0.86 ms edit+layout / ~0.54 ms scroll frame / ~1.8 ms cold first frame at 100,000 lines; GUI frames add cached QTextLayout shaping and QPainter drawing for visible runs only).

Status

Beta. Developed and tested on Fedora 44 with KDE Plasma 6 (KWin 6.8).

Architectural Trade-offs & Known Limitations

KMark renders directly from a single UTF-8 Rope onto a custom QPainter DisplayList rather than converting Markdown into a QTextDocument or embedding KTextEditor. This avoids lossy Markdown <-> AST round-trips and makes switching between Formatted (WYSIWYG), Live Preview, Markdown Source, and Plain Text an instant O(1) projection change, at the cost of not inheriting Qt's rich-text widget subsystems automatically:

• Accessibility (QAccessible): Screen-reader / assistive-technology exposure for the custom canvas viewport is not yet implemented.
• BiDi / RTL & Complex Script Shaping: Left-to-right Latin, CJK, and emoji grapheme clusters are supported via UTF-16-aligned QTextLayout measurement, but right-to-left (RTL) bidirectional paragraph layout is not yet implemented.
• Spell Checking: KDE Sonnet inline spell-checking is not yet integrated.
• Translations (i18n): The UI currently ships compiled-in English and German strings (qt-shell/src/I18n.h); full GNU gettext .po / ki18n catalog extraction for community translations is planned.

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Layered Architecture (L0 -> L5)

crates/
  buffer      L0  Persistent Copy-on-Write Rope, auto-encoding (UTF-8/UTF-16/CP1252), atomic symlink-safe save, Undo/Redo
  syntax      L1  Exact byte-offset CommonMark/GFM block parser, diff-window incremental reparse, 2D table AST, HTML5 export
  layout      L2  Modular single-buffer layout engine (context, inline, 2D table, hit-test), BlockHeightCache, DisplayList
  engine      L3  Multi-tab session, command registry, armed formatting, RegEx search/replace, multi-tab crash recovery
  ffi         L4  Panic-safe, poison-guarded C ABI (`kmark_ffi.h`) with single-pass QTextLayout & image callbacks
apps/
  kmark-cli   --  Headless CLI (`info`, `outline`, `html`, `commands`, `bench`)
qt-shell/     L5  Native C++20 Qt6 / KDE Frameworks 6 GUI (`MainWindow`, `EditorViewport`, `SettingsDialog`, `AppSettings`)

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Building & Local Installation

Prerequisites

• Rust toolchain (1.90+, cargo)
• CMake (3.22+), C++20 compiler (g++ or clang++)
• Qt6 (Core, Gui, Widgets, PrintSupport) and optional KDE Frameworks 6 (XmlGui, ConfigWidgets, CoreAddons, I18n)

Fedora / RHEL / openSUSE:

sudo dnf install cmake gcc-c++ cargo rust qt6-qtbase-devel \
    kf6-kxmlgui-devel kf6-kconfigwidgets-devel kf6-kcoreaddons-devel kf6-ki18n-devel

Debian / Ubuntu / KDE neon:

sudo apt install cmake g++ cargo rustc qt6-base-dev \
    libkf6xmlgui-dev libkf6configwidgets-dev libkf6coreaddons-dev libkf6i18n-dev

(Note: If kf6-*-dev packages are not installed, CMake automatically falls back to pure Qt6 mode.)

Quick Local User Install (~/.local)

Install kmark, kmark-cli, the scalable SVG icon, .desktop launcher, AppStream metadata, and kmarkui.rc into ~/.local without root privileges:

./scripts/install-local.sh

To remove the local installation cleanly:

./scripts/uninstall-local.sh

Manual CMake Build & Tests

cargo test --workspace
cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build -j
./build/kmark

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Building Distribution Packages (.deb, .rpm, .tar.gz)

Build release packages locally via CPack / helper scripts:

./scripts/build-packages.sh

Generated artifacts are placed in dist/ (kmark-0.1.0-linux-x86_64.tar.gz, .deb, .rpm, and SHA256SUMS).

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About the development

KMark was developed with extensive help from AI. The code, the tests and the documentation were written by Google's Gemini and Anthropic's Claude under my direction. Requirements, design decisions, review and testing are my own.

License

Copyright (C) 2026 KMark Contributors. Licensed under the GNU General Public License v3.0 or later (GPL-3.0-or-later).