Global mode and instance mode

discoman · February 2016

INSTANCE MODE

var sketch = function( p ) {

  var x = 100; 
  var y = 100;

  p.setup = function() {
    p.createCanvas(700, 410);
  };

  p.draw = function() {
    p.background(0);
    p.fill(255);
    p.rect(x,y,50,50);
  };
};

var myp5 = new p5(sketch);

GLOBAL MODE

     var x = 100;
     var y = 100;

     function setup() {
       createCanvas(200,200);
     }

     function draw() {
       background(0);
       fill(255);
       ellipse(x,y,50,50);
     }

I have run through the source of p5.js but I am not sure how it works in both modes(global and instance) and how it detects which mode the user is using. I guess it has to do something with instance object _pInst which gets passed through p5.Element. Also in functions we find -

var ctx = this._pInst || this;

So my guess it that it takes for both cases in this OR statement.

Please correct me on this if I am wrong.

blindfish · February 2016

The answer is in core.js. context is assigned either to window or the containing object... The latter is far more sane - polluting the global scope is bad practice - though then requires a reference to the container to access p5 methods/properties.

Edit: Note that at first run context is always assigned to the 'containing object' (since _isGlobal starts out false). However in global mode this will always be the browser's window object :((

In instance mode it's the p5 object instantiated with new p5(sketch);

GoToLoop · February 2016

https://GitHub.com/processing/p5.js/blob/master/src/app.js#L71

if (document.readyState === 'complete') {
  _globalInit();
} else {
  window.addEventListener('load', _globalInit , false);
}

var _globalInit = function() {
  if (!window.PHANTOMJS && !window.mocha) {
    // If there is a setup or draw function on the window
    // then instantiate p5 in "global" mode
    if((window.setup && typeof window.setup === 'function') ||
      (window.draw && typeof window.draw === 'function')) {
      new p5();
    }
  }
};

GoToLoop · February 2016

https://GitHub.com/processing/p5.js/blob/master/src/core/core.js#L37
var p5 = function(sketch, node, sync) {

https://GitHub.com/processing/p5.js/blob/master/src/core/core.js#L450

  // If the user has created a global setup or draw function,
  // assume "global" mode and make everything global (i.e. on the window)
  if (!sketch) {
    this._isGlobal = true;
    // Loop through methods on the prototype and attach them to the window
    for (var p in p5.prototype) {
      if(typeof p5.prototype[p] === 'function') {
        var ev = p.substring(2);
        if (!this._events.hasOwnProperty(ev)) {
          window[p] = p5.prototype[p].bind(this);
        }
      } else {
        window[p] = p5.prototype[p];
      }
    }
    // Attach its properties to the window
    for (var p2 in this) {
      if (this.hasOwnProperty(p2)) {
        window[p2] = this[p2];
      }
    }

  } else {
    // Else, the user has passed in a sketch closure that may set
    // user-provided 'setup', 'draw', etc. properties on this instance of p5
    sketch(this);
  }

GoToLoop · February 2016

From those source excerpts above, p5.js pollutes the global scope every time it is instantiated w/o passing a sketch to it as its 1st argument.
To mark such momentous event, it also assigns true to _isGlobal. >:)
From "app.js" @ _globalInit(), if it finds setup() or draw() as functions in the global scope, it auto-instantiates a p5 for us.
It also makes sure to call _globalInit() only when page is completely loaded.
So it's relatively impervious to the order our setup() & draw() are ready in "Global Mode". \m/

discoman · February 2016

To mark such momentous event, it also assigns true to _isGlobal.

laughed hell hard. Thanks for the explanation @blindfish and @GoToLoop. Really appreciate it. \m/

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