1 files changed, 44 insertions, 0 deletions
diff --git a/testing/web-platform/tests/webaudio/resources/audio-param.js b/testing/web-platform/tests/webaudio/resources/audio-param.js
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index 0000000000..bc33fe8a21
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+++ b/testing/web-platform/tests/webaudio/resources/audio-param.js
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+// Define functions that implement the formulas for AudioParam automations.
+
+// AudioParam linearRamp value at time t for a linear ramp between (t0, v0) and
+// (t1, v1).  It is assumed that t0 <= t.  Results are undefined otherwise.
+function audioParamLinearRamp(t, v0, t0, v1, t1) {
+  if (t >= t1)
+    return v1;
+  return (v0 + (v1 - v0) * (t - t0) / (t1 - t0))
+}
+
+// AudioParam exponentialRamp value at time t for an exponential ramp between
+// (t0, v0) and (t1, v1). It is assumed that t0 <= t.  Results are undefined
+// otherwise.
+function audioParamExponentialRamp(t, v0, t0, v1, t1) {
+  if (t >= t1)
+    return v1;
+  return v0 * Math.pow(v1 / v0, (t - t0) / (t1 - t0));
+}
+
+// AudioParam setTarget value at time t for a setTarget curve starting at (t0,
+// v0) with a final value of vFainal and a time constant of timeConstant.  It is
+// assumed that t0 <= t.  Results are undefined otherwise.
+function audioParamSetTarget(t, v0, t0, vFinal, timeConstant) {
+  return vFinal + (v0 - vFinal) * Math.exp(-(t - t0) / timeConstant);
+}
+
+// AudioParam setValueCurve value at time t for a setValueCurve starting at time
+// t0 with curve, curve, and duration duration.  The sample rate is sampleRate.
+// It is assumed that t0 <= t.
+function audioParamSetValueCurve(t, curve, t0, duration) {
+  if (t > t0 + duration)
+    return curve[curve.length - 1];
+
+  let curvePointsPerSecond = (curve.length - 1) / duration;
+
+  let virtualIndex = (t - t0) * curvePointsPerSecond;
+  let index = Math.floor(virtualIndex);
+
+  let delta = virtualIndex - index;
+
+  let c0 = curve[index];
+  let c1 = curve[Math.min(index + 1, curve.length - 1)];
+  return c0 + (c1 - c0) * delta;
+}