Add resonant filter to C++ synth

This change adds a (single) resonant filter to the C++ synth unit, and
wires up both USB MIDI and on-screen controls for cutoff and resonance.

Also fixes a bug in KnobView which caused the knob value to jump around.

android/res/layout/piano2.xml

@@ -0,0 +1,69 @@
+<?xml version="1.0" encoding="utf-8"?>
+<TableLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res/com.google.synthesizer"
+    android:id="@+id/TableLayout01"
+    android:layout_width="fill_parent"
+    android:layout_height="fill_parent"
+    android:stretchColumns="*"
+    android:shrinkColumns="*">
+  <TableRow>
+    <TextView
+        android:text="@string/cutoff"
+        android:id="@+id/cutoffLabel"
+        android:gravity="center_horizontal" />
+    <TextView
+        android:text="@+string/resonance"
+        android:id="@+id/resonanceLabel"
+        android:gravity="center_horizontal" />
+    <TextView
+        android:text=""
+        android:id="@+id/emptyLabel"
+        android:gravity="center_horizontal" />
+    <TextView
+        android:text=""
+        android:id="@+id/emptyLabel"
+        android:gravity="center_horizontal" />
+    <TextView
+        android:text=""
+        android:id="@+id/emptyLabel"
+        android:gravity="center_horizontal" />
+    <TextView
+        android:text=""
+        android:id="@+id/emptyLabel"
+        android:gravity="center_horizontal" />
+  </TableRow>
+  <TableRow>
+    <com.google.synthesizer.android.widgets.knob.KnobView
+        android:id="@+id/cutoffKnob"
+        app:value="1.0"
+        app:min="0"
+        app:max="1"
+        android:layout_margin="2px" />
+    <com.google.synthesizer.android.widgets.knob.KnobView
+        android:id="@+id/resonanceKnob"
+        app:value="0.0"
+        app:min="0"
+        app:max="1"
+        android:layout_margin="2px" />
+    <Spinner
+        android:id="@+id/presetSpinner"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_span="4" />
+  </TableRow>
+  <TableRow>
+    <LinearLayout
+        android:layout_height="fill_parent"
+        android:layout_span="6"
+        android:orientation="vertical">
+      <com.google.synthesizer.android.widgets.piano.PianoView
+          android:id="@+id/piano"
+          android:layout_width="fill_parent"
+          android:layout_height="wrap_content"
+          android:layout_weight="1"
+          app:octaves="2"
+          app:first_octave="4" />
+    </LinearLayout>
+  </TableRow>
+</TableLayout>

android/res/values/strings.xml

@@ -47,6 +47,7 @@
 
   <!-- Low Pass Filter -->
   <string name="cutoff">Cutoff</string>
+  <string name="resonance">Resonance</string>
 
   <!-- Amp -->
   <string name="attack">Attack</string>

android/src/com/google/synthesizer/android/ui/PianoActivity2.java

@@ -39,10 +39,10 @@ import android.widget.AdapterView.OnItemSelectedListener;
 import android.widget.ArrayAdapter;
 import android.widget.Spinner;
 import android.widget.TextView;
-import android.widget.ToggleButton;
 
 import com.google.synthesizer.R;
 import com.google.synthesizer.android.AndroidGlue;
+import com.google.synthesizer.android.widgets.knob.KnobListener;
 import com.google.synthesizer.android.widgets.knob.KnobView;
 import com.google.synthesizer.android.widgets.piano.PianoView;
 
@@ -57,10 +57,11 @@ public class PianoActivity2 extends Activity {
     super.onCreate(savedInstanceState);
     getWindow().addFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN |
             WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
-    setContentView(R.layout.piano);
+    setContentView(R.layout.piano2);
 
     piano_ = (PianoView)findViewById(R.id.piano);
-    volumeKnob_ = (KnobView)findViewById(R.id.volumeKnob);
+    cutoffKnob_ = (KnobView)findViewById(R.id.cutoffKnob);
+    resonanceKnob_ = (KnobView)findViewById(R.id.resonanceKnob);
     presetSpinner_ = (Spinner)findViewById(R.id.presetSpinner);
 
     androidGlue_ = new AndroidGlue();
@@ -89,6 +90,20 @@ public class PianoActivity2 extends Activity {
       public void onNothingSelected(AdapterView<?> parent) {
       }
     });
+    
+    cutoffKnob_.setKnobListener(new KnobListener() {
+      public void onKnobChanged(double newValue) {
+        int value = (int)Math.round(newValue * 127);
+        androidGlue_.onController(0, 1, value);
+      }      
+    });
+    resonanceKnob_.setKnobListener(new KnobListener() {
+      public void onKnobChanged(double newValue) {
+        int value = (int)Math.round(newValue * 127);
+        androidGlue_.onController(0, 2, value);
+      }      
+    });
+    
     piano_.bindTo(androidGlue_);
     if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH) {
       tryConnectUsb();
@@ -134,8 +149,8 @@ public class PianoActivity2 extends Activity {
           for (int i = 0; i < nBytes; i += 4) {
             int codeIndexNumber = buf[i] & 0xf;
             int payloadBytes = 0;
-            if (codeIndexNumber == 8 || codeIndexNumber == 9) {
+            if (codeIndexNumber == 8 || codeIndexNumber == 9 || codeIndexNumber == 11 ||
-              // TODO: pitchbend, control, etc
+                    codeIndexNumber == 14) {
               payloadBytes = 3;
             } else if (codeIndexNumber == 12) {
               payloadBytes = 2;
@@ -173,6 +188,7 @@ public class PianoActivity2 extends Activity {
   
   private AndroidGlue androidGlue_;
   private PianoView piano_;
-  private KnobView volumeKnob_;
+  private KnobView cutoffKnob_;
+  private KnobView resonanceKnob_;
   private Spinner presetSpinner_;
 }

android/src/com/google/synthesizer/android/widgets/knob/KnobView.java

@@ -74,7 +74,7 @@ public class KnobView extends View {
   public boolean onTouchEvent(MotionEvent event) {
     int action = event.getAction();
     switch (action) {
-      case MotionEvent.ACTION_POINTER_DOWN: {
+      case MotionEvent.ACTION_DOWN: {
         // Just record the current finger position.
         getDrawingRect(rect_);
         previousX_ = event.getX() - rect_.centerX();
@@ -116,7 +116,7 @@ public class KnobView extends View {
         break;
       }
       
-      case MotionEvent.ACTION_POINTER_UP: {
+      case MotionEvent.ACTION_UP: {
         break;
       }
     }

cpp/src/module.h

@@ -14,6 +14,9 @@
  * limitations under the License.
  */
 
+#ifndef SYNTH_MODULE_H
+#define SYNTH_MODULE_H
+
 #include <stdint.h>
 
 class Module {
@@ -23,3 +26,6 @@ class Module {
   virtual void process(const int32_t **inbufs, const int32_t *control_in,
 					   const int32_t *control_last, int32_t **outbufs) = 0;
 };
+
+#endif  // SYNTH_MODULE_H
+

cpp/src/resofilter.cc

@@ -14,7 +14,8 @@
  * limitations under the License.
  */
 
-#include "module.h"
+#include "synth.h"
+#include "freqlut.h"
 #include "resofilter.h"
 
 double this_sample_rate;
@@ -30,8 +31,8 @@ ResoFilter::ResoFilter() {
 }
 
 int32_t compute_alpha(int32_t logf) {
-  // TODO
+  // TODO: better tuning
-  return 1 << 21;
+  return min(1 << 24, Freqlut::lookup(logf));
 }
 
 void ResoFilter::process(const int32_t **inbufs, const int32_t *control_in,
@@ -42,6 +43,12 @@ void ResoFilter::process(const int32_t **inbufs, const int32_t *control_in,
   int32_t k = control_last[1];
   int32_t k_in = control_in[1];
   int32_t delta_k = (k_in - k) >> lg_n;
+  if ((((int64_t)alpha_in * (int64_t)k_in) >> 24) > 1 << 24) {
+    k_in = ((1 << 30) / alpha_in) << 18;
+  }
+  if ((((int64_t)alpha * (int64_t)k) >> 24) > 1 << 24) {
+    k = ((1 << 30) / alpha) << 18;
+  }
   const int32_t *ibuf = inbufs[0];
   int32_t *obuf = outbufs[0];
   int x0 = x[0];

cpp/src/resofilter.h

@@ -14,6 +14,11 @@
  * limitations under the License.
  */
 
+#ifndef SYNTH_RESOFILTER_H_
+#define SYNTH_RESOFILTER_H_
+
+#include "module.h"
+
 class ResoFilter : Module {
  public:
   ResoFilter();
@@ -25,3 +30,5 @@ class ResoFilter : Module {
  private:
   int32_t x[4];
 };
+
+#endif  // SYNTH_RESOFILTER_H_

cpp/src/synth_unit.cc

@@ -44,6 +44,8 @@ SynthUnit::SynthUnit(RingBuffer *ring_buffer) {
   memcpy(patch_data_, epiano, sizeof(epiano));
   current_patch_ = 0;
   current_note_ = 0;
+  filter_control_[0] = 258847126;
+  filter_control_[1] = 0;
 }
 
 // Transfer as many bytes as possible from ring buffer to input buffer.
@@ -97,6 +99,17 @@ int SynthUnit::ProcessMidiMessage(const uint8_t *buf, int buf_size) {
       return 3;
     }
     return 0;
+  } else if (cmd_type == 0xb0) {
+    if (buf_size >= 3) {
+      int controller = buf[1];
+      int value = buf[2];
+      if (controller == 1) {
+        filter_control_[0] = 129423563 + value * 1019083;
+      } else if (controller == 2) {
+        filter_control_[1] = value * 528416;
+      }
+      return 3;
+    } return 0;
   } else if (cmd_type == 0xc0) {
     if (buf_size >= 2) {
       // program change
@@ -149,6 +162,7 @@ void SynthUnit::GetSamples(int n_samples, int16_t *buffer) {
 
   for (int i = 0; i < n_samples; i += N) {
     int32_t audiobuf[N];
+    int32_t audiobuf2[N];
     for (int j = 0; j < N; ++j) {
       audiobuf[j] = 0;
     }
@@ -157,8 +171,11 @@ void SynthUnit::GetSamples(int n_samples, int16_t *buffer) {
         active_note_[note].dx7_note->compute(audiobuf);
       }
     }
+    const int32_t *bufs[] = { audiobuf };
+    int32_t *bufs2[] = { audiobuf2 };
+    filter_.process(bufs, filter_control_, filter_control_, bufs2);
     for (int j = 0; j < N; ++j) {
-      int32_t val = audiobuf[j] >> 4;
+      int32_t val = audiobuf2[j] >> 4;
       int clip_val = val < -(1 << 24) ? 0x8000 : val >= (1 << 24) ? 0x7fff :
         val >> 9;
       // TODO: maybe some dithering?

cpp/src/synth_unit.h

@@ -16,6 +16,7 @@
 
 #include "dx7note.h"
 #include "ringbuffer.h"
+#include "resofilter.h"
 
 struct ActiveNote {
   int midi_note;
@@ -35,7 +36,7 @@ class SynthUnit {
   int ProcessMidiMessage(const uint8_t *buf, int buf_size);
 
   RingBuffer *ring_buffer_;
-  static const int max_active_notes = 16;
+  static const int max_active_notes = 8;
   ActiveNote active_note_[max_active_notes];
   int current_note_;
   uint8_t input_buffer_[8192];
@@ -43,4 +44,7 @@ class SynthUnit {
 
   uint8_t patch_data_[4096];
   int current_patch_;
+
+  ResoFilter filter_;
+  int32_t filter_control_[2];
 };