Upgrade the Flanger effect (#5873)

Updates QuadratureLfo and moves to include/

Co-authored-by: Hyunjin Song <tteu.ingog@gmail.com>
Co-authored-by: Dave French <dave.french3@googlemail.com>

include/QuadratureLfo.h

@@ -0,0 +1,96 @@
+/*
+ * quadraturelfo.h - defination of QuadratureLfo class.
+ *
+ * Copyright (c) 2014 David French <dave/dot/french3/at/googlemail/dot/com>
+ *
+ * This file is part of LMMS - https://lmms.io
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program (see COPYING); if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301 USA.
+ *
+ */
+
+#ifndef QUADRATURELFO_H
+#define QUADRATURELFO_H
+
+#include "lmms_math.h"
+
+class QuadratureLfo
+{
+public:
+	QuadratureLfo( int sampleRate ) :
+		m_frequency(0),
+		m_phase(0),
+		m_offset(D_PI / 2)
+	{
+		setSampleRate(sampleRate);
+	}
+
+	~QuadratureLfo() = default;
+
+	inline void setFrequency( double frequency )
+	{
+		if( frequency < 0 || frequency > m_samplerate / 2.0 || frequency == m_frequency )
+		{
+			return;
+		}
+		m_frequency = frequency;
+		m_increment = m_frequency * m_twoPiOverSr;
+	}
+
+
+	inline void restart()
+	{
+		m_phase = 0;
+	}
+
+
+	inline void setSampleRate ( int samplerate )
+	{
+		m_samplerate = samplerate;
+		m_twoPiOverSr = F_2PI / samplerate;
+		m_increment = m_frequency * m_twoPiOverSr;
+	}
+
+
+	inline void setOffset( double offsetVal )
+	{
+		m_offset = offsetVal;
+	}
+
+
+	void tick( float *l, float *r )
+	{
+		*l = sinf( m_phase );
+		*r = sinf( m_phase + m_offset );
+		m_phase += m_increment;
+
+		while (m_phase >= D_2PI)
+		{
+			m_phase -= D_2PI;
+		}
+	}
+
+private:
+	double m_frequency;
+	double m_phase;
+	double m_increment;
+	double m_twoPiOverSr;
+	double m_offset;
+	int m_samplerate;
+
+};
+
+#endif // QUADRATURELFO_H