Add VUMeter class to dsp library

include/dsp/vumeter.hpp

@@ -0,0 +1,32 @@
+#pragma once
+
+#include "math.hpp"
+
+
+namespace rack {
+
+
+struct VUMeter {
+	/** Decibel level difference between adjacent meter lights */
+	float dBInterval = 3.0;
+	float dBScaled;
+	/** Value should be scaled so that 1.0 is clipping */
+	void setValue(float v) {
+		dBScaled = log10f(fabsf(v)) * 20.0 / dBInterval;
+	}
+	/** Returns the brightness of the light indexed by i
+	Light 0 is a clip light (red) which is either on or off.
+	All others are smooth lights which are fully bright at -dBInterval*i and higher, and fully off at -dBInterval*(i-1).
+	*/
+	float getBrightness(int i) {
+		if (i == 0) {
+			return (dBScaled >= 0.0) ? 1.0 : 0.0;
+		}
+		else {
+			return clampf(dBScaled + i, 0.0, 1.0);
+		}
+	}
+};
+
+
+} // namespace rack