Heartbeat function in HLSL

heartbeat.hlsl

// Approximates a heartbeat
// Roughly approximates mathematical formula:
//	x = t * f * PI
//  	y = h * sin(x)^(2 * p + 1) * sin(x + d)
//  where 
//	f is frequency in Hz if t is fractional seconds
//	p is a power factor (the "slope" of the main upswing of the wave)
//      d is an "offset" that shifts the peak and trough heights
//      h is an overall height factor
//
// Example function:
// 	http://www.iquilezles.org/apps/graphtoy/?f1(x)=pow(sin(2*3.14159*x),31)*sin(2*3.14159*x+1.4)*4
//  where:
//	(f) frequency is 2Hz
//	(p) power is 15 (so, an exponent of 2p+1 = 31)
//	(d) offset is 1.4
//	(h) height is multiplied by 4 to get it roughly inside of [-1,1]
float heartbeat(float t, float frequency, float power, float offset, float height) {
	float x = t * frequency * 3.1415926535897932384626433832795;
	float s1 = sin(x);
	float s2 = sin(x + offset);
	// pow(x,y) in HLSL isn't defined for x < 0, 
	// so take advantage of the fact that squaring gets rid of the sign anyhow
	float a = pow(s1 * s1, power); // i.e., pow(abs(s1), 2 * power)
	a *= s1; // one more power to get (2*n+1)th power, with original sign
	return height * a * s2;
}