/* Resonant 2-Pole LP 
 * Parameter a is the cutoff frequency, parameter b is the resonance, parameter c can be used to set the maximum cutoff frequency 
 * and parameter d to finetune the resonance.
 * Algorithm is from www.musicdsp.org. Posted by Daniel Werner from http://experimentalscene.com/
 * The algorithm is a modified version of the tweaked butterworth lowpass filter by Patrice Tarrabia posted on musicdsp.org's archives.
 */

import org.jvaptools.scripteffect.*;

org.jvaptools.VstPluginImpl plugin;

float pi;
float samplerate;
float c, csq, resonance, q, a0, a1, a2, b1, b2;
float in11,in12,in21,in22,out11,out12,out21,out22;
float p1smooth;
float p1filtercoeff;

public void init(org.jvaptools.VstPluginImpl owner) {
  this.plugin=owner; 
  pi=3.1415926535897932384626433832795f;
  samplerate=44100.0f;
  in11=0;in12=0;in21=0;in22=0;
  out11=0;out12=0;out21=0;out22=0;
  this.plugin.setParameter("a","1.0");
  this.plugin.setParameter("b","0.8");
  this.plugin.setParameter("c","1.0");
  this.plugin.setParameter("d","0.99");
  this.p1smooth=1.0f;
 this.p1filtercoeff=0.0007f;
}

public void close() {}

public void onMidiEvent(javax.sound.midi.MidiMessage message, long timeStamp) {}


// Warning: Parameter a,b,c and d from the host are called p1,p2,p3 and p4!
public void processReplacing(vstmain plugin,float p1,float p2,float p3,float p4,float[][] inputs, float[][] outputs, int sampleFrames)
{ 
  float[] out1 = outputs[0];
  float[] out2 = outputs[1];
  float[] in1 = inputs[0];
  float[] in2 = inputs[1];
  
 
  for (int i = 0; i < sampleFrames; i++) {    
    if((i%20)==0) {
      p1smooth=p1filtercoeff*p1+(1.0f-p1filtercoeff)*p1smooth;
      c = 1.0f / ((float)java.lang.Math.tan(pi * ((0.001f+p1smooth*p3) / 2.15f)));
      csq = c * c;
      q = (float)java.lang.Math.sqrt(2.0f) * (1-p2)*(1-p4);
      a0 = 1.0f / (1.0f + (q * c) + (csq));
      a1 = 2.0f * a0;
      a2 = a0;
      b1 = (2.0f * a0) * (1.0f - csq);
      b2 = a0 * (1.0f - (q * c) + csq);
    }
    out1[i] = in1[i]*a0 + in11*a1 + in12*a2 - out11*b1 - out12*b2;
    out2[i] = in2[i]*a0 + in21*a1 + in22*a2 - out21*b1 - out22*b2;
    out12=out11; out11=out1[i]; in12=in11; in11=in1[i];
    out22=out21; out21=out2[i]; in22=in21; in21=in1[i];
  } 
}