Despite this being "easier" than some of the alternatives, it is nonetheless an API I have zero experience with, and the implementation was built with code that I would have no idea how to write, although once written, I can get the gist. Here is the "detectNodWithPitch" function as an example (that's how a "nod" is detected - the pitch of the face is determined, and then the change of pitch is what is considered a nod, of course, this is not entirely straightforward).
```
- (void)detectNodWithPitch:(float)pitch { // Get sensitivity-adjusted threshold // At sensitivity 0: threshold = kMaxThreshold degrees (requires strong nod) // At sensitivity 1: threshold = kMaxThreshold - kThresholdRange degrees (very sensitive) float sens = _cppOwner->getSensitivity(); float threshold = NodDetectionConstants::kMaxThreshold - (sens * NodDetectionConstants::kThresholdRange);
// Debounce check
NSTimeInterval now = [NSDate timeIntervalSinceReferenceDate];
if (now - _lastNodTime < _debounceSeconds)
return;
// Initialize baseline if needed
if (!_hasBaseline)
{
_baselinePitch = pitch;
_hasBaseline = YES;
return;
}
// Calculate delta: positive when head tilts down from baseline
// (pitch increases when head tilts down, so delta = pitch - baseline)
float delta = pitch - _baselinePitch;
// Update nod progress for UI meter
// Normalize against a fixed max (20 degrees) so the bar shows absolute head movement
// This allows the threshold line to move with sensitivity
constexpr float kMaxDisplayDelta = 20.0f;
float progress = (delta > 0.0f) ? std::min(delta / kMaxDisplayDelta, 1.0f) : 0.0f;
_cppOwner->setNodProgress(progress);
if (!_nodStarted)
{
_cppOwner->setNodInProgress(false);
// Check if nod is starting (head tilting down past nod start threshold)
if (delta > threshold * NodDetectionConstants::kNodStartFactor)
{
_nodStarted = YES;
_maxPitchDelta = delta;
_cppOwner->setNodInProgress(true);
DBG("HeadNodDetector: Nod started, delta=" << delta);
}
else
{
// Adapt baseline slowly when not nodding
_baselinePitch = _baselinePitch * (1.0f - _baselineAdaptRate) + pitch * _baselineAdaptRate;
}
}
else
{
// Track maximum delta during nod
_maxPitchDelta = std::max(_maxPitchDelta, delta);
// Check if head has returned (delta decreased below return threshold)
if (delta < threshold * _returnFactor)
{
// Nod complete - check if it was strong enough
if (_maxPitchDelta > threshold)
{
DBG("HeadNodDetector: Nod detected! maxDelta=" << _maxPitchDelta << " threshold=" << threshold);
_lastNodTime = now;
_cppOwner->handleNodDetected();
}
else
{
DBG("HeadNodDetector: Nod too weak, maxDelta=" << _maxPitchDelta << " < threshold=" << threshold);
}
// Reset nod state
_nodStarted = NO;
_maxPitchDelta = 0.0f;
_baselinePitch = pitch; // Reset baseline to current position
_cppOwner->setNodInProgress(false);
_cppOwner->setNodProgress(0.0f);
}
}@end
```