gistfile1.c

static vec2_t bezier_firstDerivative(bezier_t curve, float t)
{
	vec2_t out;
	vec3_t derivControlPoints[3];
	derivControlPoints[0] = vec3_sub(curve.controlPoints[1], curve.controlPoints[0]);
	derivControlPoints[1] = vec3_sub(curve.controlPoints[2], curve.controlPoints[1]);
	derivControlPoints[2] = vec3_sub(curve.controlPoints[3], curve.controlPoints[2]);
	
	float mt = 1.0f - t;
	float coef0 = powf(mt, 2.0f);
	float coef1 = 2.0f * mt * t;
	float coef2 = powf(t, 2.0f);
	
	vec3_t p0 = vec3_scalarMul(derivControlPoints[0], coef0);
	vec3_t p1 = vec3_scalarMul(derivControlPoints[1], coef1);
	vec3_t p2 = vec3_scalarMul(derivControlPoints[2], coef2);
	
	out = vec3_add(p0, vec3_add(p1, p2));
	
	return out;
}