simple interceptor of webgl context calls (for when spector.js is an overkill)

README.md

the code should be called right after we obtain the GL context. Don't forget to reset/edit ignoreCommands if you intend to capture some of those.

example usages:

fakeGl.captureOperations(40)
...
fakeGl.ignoreCommands = []
fakeGl.setHistogramMode(true)
fakeGl.captureFrames(1)
...
fakeGl.setHistogramMode(false)

webglContextSpy.js

var originalGl = gl;
var changedGl = {};

var fakeGl = {
  ignoreCommands: 'activeTexture bindBuffer bindFramebuffer bufferSubData clear clearColor uniform2f vertexAttribPointer viewport'.split(' '),
  setHistogramMode(bool) {
    if (bool) {
      fakeGl.histogram = {};
    } else {
      var h = fakeGl.histogram;
      delete fakeGl.histogram;
      return h;
    }
  },
  captureOperations: function(numOps) {
    fakeGl.commandsLeftToCapture = numOps;
    fakeGl.capture = true;
  },
  captureFrames: function(numFrames) {
    fakeGl.framesToCapture = numFrames;
    fakeGl.capture = true;
    function onFrame() {
      console.warn('***** GL frame #' + fakeGl.framesToCapture + ' *****');
      --fakeGl.framesToCapture;
      if (!fakeGl.framesToCapture) {
        fakeGl.capture = false;
      } else {
        requestAnimationFrame(onFrame);
      }
    }
    requestAnimationFrame(onFrame);
  }
};
window.fakeGl = fakeGl;

function fakeMethod(methodName) {
  return function() {
    if (fakeGl.capture && fakeGl.ignoreCommands.indexOf(methodName) === -1) {

      if (fakeGl.histogram) {
        if (!fakeGl.histogram[methodName]) fakeGl.histogram[methodName] = 1;
        else ++fakeGl.histogram[methodName];
      } else {
        var args = Array.prototype.slice.apply(arguments);
        console.warn('gl.' + methodName, args);
      }

      if (fakeGl.commandsLeftToCapture) {
        --fakeGl.commandsLeftToCapture;
        if (!fakeGl.commandsLeftToCapture) { fakeGl.capture = false; }
      }
    }
    return originalGl[methodName].apply(originalGl, arguments);
  }
}

for (var k in gl) {
  changedGl[k] = typeof gl[k] === 'function' ? fakeMethod(k) : originalGl[k];
}
changedGl.prototype = originalGl;
gl = changedGl;