in js/reveal.js [5645:5676]
function Playback( container, progressCheck ) {
// Cosmetics
this.diameter = 100;
this.diameter2 = this.diameter/2;
this.thickness = 6;
// Flags if we are currently playing
this.playing = false;
// Current progress on a 0-1 range
this.progress = 0;
// Used to loop the animation smoothly
this.progressOffset = 1;
this.container = container;
this.progressCheck = progressCheck;
this.canvas = document.createElement( 'canvas' );
this.canvas.className = 'playback';
this.canvas.width = this.diameter;
this.canvas.height = this.diameter;
this.canvas.style.width = this.diameter2 + 'px';
this.canvas.style.height = this.diameter2 + 'px';
this.context = this.canvas.getContext( '2d' );
this.container.appendChild( this.canvas );
this.render();
}