Function build

src/fx/waveform.js:78–163

* Builds each waveform for the page.

()

   * Builds each waveform for the page.
   */
  function build() {
    if (config.web_audio_api_available) {
      /*
        If we don't have the wave form built, we need to build the waveform by loading
        the src with an array buffer.
      */
      if (
        config.waveforms.built[
          Math.abs(
            config.audio.src.split("").reduce(function(a, b) {
              a = (a << 5) - a + b.charCodeAt(0);
              return a & a;
            }, 0)
          )
        ] == undefined
      ) {
        /*
          Initializes a new XML Http Request.
        */
        var req = new XMLHttpRequest();

        /*
          Opens the src parameter for the audio file to read in.
        */
        req.open("GET", config.audio.src, true);
        req.responseType = "arraybuffer";

        /*
          When the ready state changes, check to see if we can render the
          wave form.
        */
        req.onreadystatechange = function(e) {
          /*
            When the request is complete, then we begin decoding the
            audio to build the waveform.
          */
          if (req.readyState == 4) {
            /*
              If the status is 200 means the response is a success and
              we decode the audio data.
            */
            if (req.status == 200) {
              /*
                Decode the audio data and process the waveform.
              */
              config.context.decodeAudioData(req.response, function(
                bufferedAudio
              ) {
                /*
                  Set the buffer to the audio returned.
                */
                buffer = bufferedAudio;

                /*
                  Get the peaks in the audio.
                */
                peaks = getPeaks(sampleRate, buffer);