add smoothing to split eq mode transitions

util/smoother.h

@@ -0,0 +1,60 @@
+#pragma once
+
+#include "audio_math.h"
+
+namespace trnr {
+
+struct smoother {
+	float samplerate;
+	float time_samples;
+
+	float current;
+	float target;
+	float increment;
+	int32_t remaining;
+};
+
+inline void smoother_init(smoother& s, double samplerate, float time_ms, float initial_value = 0.0f)
+{
+	s.samplerate = fmax(0.0, samplerate);
+	s.time_samples = ms_to_samples(time_ms, s.samplerate);
+	s.current = initial_value;
+	s.target = initial_value;
+	s.increment = 0.0f;
+	s.remaining = 0;
+}
+
+inline void smoother_set_target(smoother& s, float newTarget)
+{
+	s.target = newTarget;
+
+	// immediate if time is zero or too short
+	if (s.time_samples <= 1.0f) {
+		s.current = s.target;
+		s.increment = 0.0f;
+		s.remaining = 0;
+		return;
+	}
+
+	int32_t n = static_cast<int32_t>(fmax(1.0f, ceilf(s.time_samples)));
+	s.remaining = n;
+	// protect against denormals / tiny differences, but we want exact reach at the end
+	s.increment = (s.target - s.current) / static_cast<float>(s.remaining);
+}
+
+// process a single sample and return the smoothed value
+inline float smoother_process_sample(smoother& s)
+{
+	if (s.remaining > 0) {
+		s.current += s.increment;
+		--s.remaining;
+		if (s.remaining == 0) {
+			// ensure exact target at the end to avoid FP drift
+			s.current = s.target;
+			s.increment = 0.0f;
+		}
+	}
+	return s.current;
+}
+
+} // namespace trnr