<!DOCTYPE html>
<html>

<head>
  <script src="../resources/js-test.js"></script>
  <script src="resources/compatibility.js"></script>
  <script src="resources/audio-testing.js"></script>
</head>

<body>
  <script>
    description('AudioBufferSourceNode: DC-driven detune modulation.');
    window.jsTestIsAsync = true;

    var sampleRate = 44100;

    // To get an observable change on detune modulation, the minimum
    // rendering length should greater than the rendering quantum.
    var renderLength = 256;
    var half = renderLength / 2;

    // With the detune of 0, the duration of impulse buffer should be 4 
    // samples (which means the interval between impulses is 4). Increasing
    // detune to 1200 (1 octave) decrease the interval to 2 samples.
    var impulseLength = 4;

    var context = new OfflineAudioContext(1, renderLength, sampleRate);
    var impulseBuffer, dcOffsetBuffer;

    var audit = Audit.createTaskRunner();


    // Task: build an impulse and DC-offset buffers for testing.
    audit.defineTask('build-buffers', function (done) {
      // 4-sample impulse sample.
      impulseBuffer = createImpulseBuffer(context, impulseLength);

      // Create a DC offset buffer with 2 values [0, 1200] for modulating
      // detune. The first half of buffer is 0 and the rest is 1200.
      dcOffsetBuffer = context.createBuffer(1, renderLength, sampleRate);
      var dcOffsetArray = dcOffsetBuffer.getChannelData(0);
      for (i = 0; i < dcOffsetArray.length; i++) {

        // Note that these values will be added to the detune AudioParam
        // value. For example, 1 DC offset value will result detune of 1200.
        dcOffsetArray[i] = i < half ? 0 : 1200;
      }

      done();
    });


    // Task: Render the actual buffer and compare with the reference.
    audit.defineTask('synthesize-verify', function (done) {
      var impulse = context.createBufferSource();
      var dcOffset = context.createBufferSource();

      impulse.buffer = impulseBuffer;
      dcOffset.buffer = dcOffsetBuffer;
      impulse.loop = true;

      impulse.connect(context.destination);
      dcOffset.connect(impulse.detune);

      impulse.start();
      dcOffset.start();

      context.startRendering().then(function (renderedBuffer) {
        var data = renderedBuffer.getChannelData(0);
        var passed = true, i = 0;
        var nextImpulseIndex = 0;

        while (i < renderLength) {
          if (i === nextImpulseIndex && data[i] === 1) {
            // From 0 to 127th element, the interval between impulses is 4. On the other
            // hand, the interval is 2 between 128th and 255th element.
            nextImpulseIndex += (i < half) ? impulseLength : impulseLength / 2;
          } else if (data[i] !== 0) {           
            // If a value is neither 0 or 1, break the loop and fail the test.
            passed = false;
            break;
          }

          i++;
        }

        if (passed) {
          testPassed('Increasing detune to 1200 decreased the interval between impulses to half.');
        } else {
          testFailed('Increasing detune produced the incorrect result' +
            'at the index ' + i + '.');
        }
      }).then(done);
    });

    audit.defineTask('finish', function (done) {
      finishJSTest();
      done();
    });

    audit.runTasks(
      'build-buffers',
      'synthesize-verify',
      'finish'
    );

    successfullyParsed = true;
  </script>
</body>

</html>