zPen is a powerful fullscreen drawing overlay tool for Linux systems written in C using Xlib. It creates a transparent drawing layer over your desktop, allowing you to annotate, sketch, and highlight anything on your screen. Perfect for presentations, tutorials, code reviews, and quick visual communication.

• Drawing Tools:

  • Freehand Drawing: Draw freehand on the screen with smoothing capabilities.
  • Rectangles: Draw rectangles by clicking and dragging.
  • Circles: Draw circles by defining the center and radius.
  • Lines: Draw straight lines by specifying start and end points.
  • Arrows: Draw arrows to point out specific areas on the screen.
  • Curly Braces: Draw opening { and closing } braces with automatic direction detection.
  • Square Brackets: Draw opening [ and closing ] brackets with automatic direction detection.
  • Text Input: Add text annotations at any position on the screen.

• Screenshot Capture:

  • Capture the current state of the screen as a screenshot and save it as a .png file.

• Undo/Redo System:

  • Full undo/redo functionality with up to 20 levels of history.
  • Standard keyboard shortcuts: Ctrl+Z for undo, Shift+Ctrl+Z for redo.
  • Backward compatibility: u key still works for undo.

• Color Selection:

  • Choose from a palette of 9 predefined colors: red, green, blue, yellow, orange, white, magenta, pink, and gray.
  • Visual color palette displayed at bottom-right corner showing all available colors.
  • Selected color is highlighted with a filled circle and white border.
  • Enhanced navigation: Use arrow keys (←/→) or spacebar to cycle colors.

• Step Counter:

  • Display a step counter for drawings made with the freehand tool.

• Use the mouse to draw on the screen.
• Click and hold to start drawing freehand shapes.
• Release the mouse button to complete the shape.

• Press the following keys to switch between drawing tools:
  • p: Pen (Freehand drawing)
  • l: Line
  • a: Arrow
  • r: Rectangle
  • c: Circle
  • k: Curly Braces { } (direction auto-detected by drag direction)
  • b: Square Brackets [ ] (direction auto-detected by drag direction)
  • t: Text input at cursor position

• Space: Cycle to next color
• ← / →: Navigate backward/forward through color palette

• Ctrl+Z: Undo last action
• Shift+Ctrl+Z: Redo last undone action
• u: Undo (backward compatibility)

• s: Capture screenshot, copy to clipboard, and exit
• f: Capture screenshot and save as PNG file

• n: Add numbered step counter
• ESC: Exit zPen

• Operating System: Linux with X Window System (X11)
• Dependencies:
  • libx11-dev - X11 development libraries
  • xclip - Clipboard management (usually pre-installed)
  • gcc - C compiler
  • make (optional, for build automation)

Ubuntu/Debian:

sudo apt install libx11-dev xclip build-essential

Fedora/CentOS/RHEL:

sudo dnf install libX11-devel xclip gcc
# or for older versions:
sudo yum install libX11-devel xclip gcc

Arch Linux:

sudo pacman -S libx11 xclip gcc

1. Clone the repository:

   git clone <repository-url>
   cd zpen

2. Compile:

   cd src
   gcc zpen.c -o zpen -lX11 -lm

3. Run:

   ./zpen

To install zPen system-wide:

# Compile
cd src
gcc zpen.c -o zpen -lX11 -lm

# Install to /usr/local/bin
sudo cp zpen /usr/local/bin/

# Now you can run zPen from anywhere
zpen

You can set up global keyboard shortcuts to launch zPen quickly:

XFCE:

xfconf-query -c xfce4-keyboard-shortcuts -n -t 'string' -p '/commands/custom/<Super>p' -s /usr/local/bin/zpen

Cinnamon (Linux Mint):

dconf write /org/cinnamon/desktop/keybindings/custom-list "['custom0']"
dconf write /org/cinnamon/desktop/keybindings/custom-keybindings/custom0/command "'/usr/local/bin/zpen'"
dconf write /org/cinnamon/desktop/keybindings/custom-keybindings/custom0/name "'zPen Drawing Tool'"
dconf write /org/cinnamon/desktop/keybindings/custom-keybindings/custom0/binding "['<Super>p']"

GNOME:

gsettings set org.gnome.settings-daemon.plugins.media-keys custom-keybindings "['/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom0/']"
gsettings set org.gnome.settings-daemon.plugins.media-keys.custom-keybinding:/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom0/ name 'zPen Drawing Tool'
gsettings set org.gnome.settings-daemon.plugins.media-keys.custom-keybinding:/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom0/ command '/usr/local/bin/zpen'
gsettings set org.gnome.settings-daemon.plugins.media-keys.custom-keybinding:/org/gnome/settings-daemon/plugins/media-keys/custom-keybindings/custom0/ binding '<Super>p'

• Curly Braces (k): Drag left-to-right for {, drag right-to-left for }
• Square Brackets (b): Drag left-to-right for [, drag right-to-left for ]

• Left Click: Set the starting point of the tool or add a point in freehand mode.
• Drag: Draw the shape.
• Release: Finish drawing the shape.

Screenshots are automatically saved in the ~/.zpen directory with timestamp-based filenames in the format imgYYYYMMDDHHMMSS.png. The directory is created automatically if it doesn't exist.

Example files:

• ~/.zpen/img20241201143052.png - Screenshot taken on Dec 1, 2024 at 14:30:52

• Screenshots: PNG format for best quality and transparency support
• Clipboard: Images are copied in PNG format for clipboard compatibility

• Single-file C application using Xlib for X11 integration
• Fullscreen transparent overlay that doesn't interfere with desktop interaction
• Memory-efficient with minimal system resource usage
• Real-time drawing with XOR graphics for smooth preview

• Path smoothing for freehand drawing with configurable smoothing levels
• Efficient undo system using pixmap snapshots (up to 20 levels)
• Minimal latency for responsive drawing experience

"Cannot open display" error:

• Ensure you're running on a system with X11 (not Wayland-only)
• Check if $DISPLAY environment variable is set: echo $DISPLAY

Missing libraries error:

• Install X11 development packages: sudo apt install libx11-dev

Permission issues with screenshots:

• Ensure ~/.zpen directory has write permissions
• Check that xclip is installed for clipboard functionality

zPen currently requires X11 and may not work on pure Wayland systems. For Wayland users:

• Use XWayland compatibility layer
• Consider running in X11 session for full functionality

Contributions are welcome! Please follow these guidelines:

1. Fork the repository and create a feature branch
2. Test your changes thoroughly on different Linux distributions
3. Follow C coding standards and maintain code documentation
4. Submit a pull request with clear description of changes

# Clone and setup development environment
git clone <repository-url>
cd zpen/src

# Compile with debug flags
gcc -g -Wall -Wextra zpen.c -o zpen -lX11 -lm

# Run with debugging
gdb ./zpen

This project is licensed under the MIT License. See the LICENSE file for full details.

• Built with Xlib for X Window System integration
• Uses stb_image_write.h for PNG file generation
• Inspired by annotation tools for presentations and tutorials

zPen combines the simplicity of a drawing tool with powerful features for annotation, documentation, and screen capture. Perfect for presentations, tutorials, code reviews, and quick visual communication.