Randomizer to implement counterbalancing for geometry alternation study. To use, define a frame with "kind": "choice" and "sampler": "geometry", as shown below, in addition to the parameters described under 'properties'.

"frames": {
    "alt-trials": {
       "sampler": "geometry",
       "kind": "choice",
       "frameType": "exp-lookit-geometry-alternation",
       "counterbalance": {
           "startPositions": [
               "left",
               "right"
           ],
           "contexts": [
               "fat",
               "skinny"
           ]
       },
       "frameOptions": {
           "triangleLineWidth": 8,
           "calibrationVideoSources": [
               {
                   "src": "https://s3.amazonaws.com/lookitcontents/geometry/webm/attention.webm",
                   "type": "video/webm"
               },
               {
                   "src": "https://s3.amazonaws.com/lookitcontents/geometry/mp4/attention.mp4",
                   "type": "video/mp4"
               }
           ],
           "trialLength": 60,
           "attnLength": 10,
           "calibrationLength": 3000,
           "fsAudio": [
               {
                   "src": "https://s3.amazonaws.com/lookitcontents/geometry/mp3/fullscreen.mp3",
                   "type": "audio/mp3"
               },
               {
                   "src": "https://s3.amazonaws.com/lookitcontents/geometry/ogg/fullscreen.ogg",
                   "type": "audio/ogg"
               }
           ],
           "triangleColor": "#056090",
           "unpauseAudio": [
               {
                   "src": "https://s3.amazonaws.com/lookitcontents/geometry/mp3/return_after_pause.mp3",
                   "type": "audio/mp3"
               },
               {
                   "src": "https://s3.amazonaws.com/lookitcontents/geometry/ogg/return_after_pause.ogg",
                   "type": "audio/ogg"
               }
           ],
           "pauseAudio": [
               {
                   "src": "https://s3.amazonaws.com/lookitcontents/geometry/mp3/pause.mp3",
                   "type": "audio/mp3"
               },
               {
                   "src": "https://s3.amazonaws.com/lookitcontents/geometry/ogg/pause.ogg",
                   "type": "audio/ogg"
               }
           ],
           "videoSources": [
               {
                   "src": "https://s3.amazonaws.com/lookitcontents/exp-physics-final/stimuli/attention/webm/attentiongrabber.webm",
                   "type": "video/webm"
               },
               {
                   "src": "https://s3.amazonaws.com/lookitcontents/exp-physics-final/stimuli/attention/mp4/attentiongrabber.mp4",
                   "type": "video/mp4"
               }
           ],
           "musicSources": [
               {
                   "src": "https://s3.amazonaws.com/lookitcontents/geometry/mp3/happy-stroll.mp3",
                   "type": "audio/mp3"
               },
               {
                   "src": "https://s3.amazonaws.com/lookitcontents/geometry/ogg/happy-stroll.ogg",
                   "type": "audio/ogg"
               }
           ],
           "calibrationAudioSources": [
               {
                   "src": "https://s3.amazonaws.com/lookitcontents/geometry/mp3/chimes.mp3",
                   "type": "audio/mp3"
               },
               {
                   "src": "https://s3.amazonaws.com/lookitcontents/geometry/ogg/chimes.ogg",
                   "type": "audio/ogg"
               }
           ]
       }
   }
}