x11-canvas-screencast

x11-canvas-screencast is a UNIX-to-HTML5-Canvas screencasting system that uses the same animation technique as the anim_encoder project.

This project's name is now a misnomer. On OS X, it does not use X11 at all.

The project includes a Qt executable, screencast, which polls the screen and mouse cursor and outputs an animation. Specifically, it writes an animation script (a CSV-separated list of steps) and a number of PNG files (one per screen capture and one per unique mouse cursor). The pack_animation.py script (based on anim_encoder.py) optimizes an animation script by creating a packed PNG file and then replacing each screen command with a blit command that copies part of the packed PNG file into the canvas.

Packing the animation can be slow, and this approach makes it easy to view and tweak the animation prior to packing it.

Prerequisites

The screencast program depends on Qt. On targets other than OS X, it also needs the XFixes extension to query the mouse cursor. The pack_animation.py script has the same dependencies as anim_encoder -- NumPy, SciPy, OpenCV, and pngcrush. On Ubuntu, install these packages:

libqt4-dev libxfixes-dev python-numpy python-scipy python-opencv pngcrush

Usage

1. Build screencast:

    $ qmake
    $ make
    

2. Capture an animation:

    $ ./screencast --rect X Y W H --output example.js
    

   Hit Enter to stop the capture. Turning on CAPS LOCK will temporarily pause the capture. Turning off CAPS LOCK returns the mouse cursor to its position before pausing the capture, then unpauses the capture.

3. Pack the animation:

    $ ./pack_animation.py example.js
    

   pack_animation.py example.js will output example_packed.js and example_packed.png.

Embedding an animation in a web page

See example/example.html for an example of embedding the player.

Include the animation's JavaScript file and player.js in the page. The player.js script defines a Player class. Construct it:

var player = Player(<animation-script-object>, "<animation-source-dir>");

The <animation-source-dir> path will be prefixed to each path in the animation script. The Player object has an element field. Add or remove it to a page. A player is initially paused; unpause it with the start method. Pause it with the pause method.

The Player object has two events:

• onload. This is called after all of the images are loaded, and after the player's canvas has been painted with the first frame.

• onloop. This is called at the end of the animation, as it is looping back to the beginning. Pause it here to prevent looping.

Caveats

I have not tested the screencast program with multiple screens or with high-DPI/Retina screens. Either situation could break badly.

On OS X, I have tested the screencast program, but not pack_animation.py. It will probably work fine if the Python dependencies are satisfied.

License

BSD license.