Initial commit of project.

source/synth.c

@@ -0,0 +1,139 @@
+#include "synth.h"
+#include <math.h>
+#include <stdlib.h>
+#include <stdint.h>
+
+#ifndef M_PI
+#define M_PI 3.14159265358979323846
+#endif
+
+void synthInit(Synth *s, float sampleRate)
+{
+    s->sampleRate       = sampleRate;
+    s->attackSec        = 0.005f;
+    s->releaseSec       = 0.050f;
+    s->dutyCycle        = 0.5f;
+    s->waveform         = WAVE_SINE;
+    s->lastStolenVoice  = 0;
+
+    for (int i = 0; i < VOICE_COUNT; i++) {
+        s->voices[i].phase     = 0.0f;
+        s->voices[i].freqHz    = 440.0f;
+        s->voices[i].amp       = 0.0f;
+        s->voices[i].targetAmp = 0.0f;
+        s->voices[i].active    = 0;
+        s->voices[i].midiNote  = -1;
+        s->pitchBend      = 0.0f;
+        s->pitchBendRange = 2.0f;
+    }
+}
+
+float waveformSample(Waveform w, float phase, float dutyCycle)
+{
+    switch (w) {
+        case WAVE_SINE:
+            return sinf(2.0f * (float)M_PI * phase);
+        case WAVE_TRIANGLE:
+            return (phase < 0.5f)
+            ? ( 4.0f * phase - 1.0f)
+            : (-4.0f * phase + 3.0f);
+        case WAVE_SAW:
+            return 2.0f * phase - 1.0f;
+        case WAVE_RAMP:
+            return 1.0f - 2.0f * phase;
+        case WAVE_PULSE:
+            return (phase < dutyCycle) ? 1.0f : -1.0f;
+        case WAVE_NOISE:
+            return ((float)rand() / (float)RAND_MAX) * 2.0f - 1.0f;
+        default:
+            return 0.0f;
+    }
+}
+
+const char *waveformName(Waveform w)
+{
+    switch (w) {
+        case WAVE_SINE:     return "Sine";
+        case WAVE_TRIANGLE: return "Triangle";
+        case WAVE_SAW:      return "Saw";
+        case WAVE_RAMP:     return "Ramp";
+        case WAVE_PULSE:    return "Pulse";
+        case WAVE_NOISE:    return "Noise";
+        default:            return "???";
+    }
+}
+
+void synthNoteOn(Synth *s, int midiNote)
+{
+    float hz = 440.0f * powf(2.0f, (midiNote - 69) / 12.0f);
+
+    for (int i = 0; i < VOICE_COUNT; i++) {
+        if (!s->voices[i].active) {
+            s->voices[i].freqHz    = hz;
+            s->voices[i].midiNote  = midiNote;
+            s->voices[i].targetAmp = 1.0f;
+            s->voices[i].active    = 1;
+            return;
+        }
+    }
+
+    // No free voice — steal round-robin
+    int i = s->lastStolenVoice % VOICE_COUNT;
+    s->lastStolenVoice++;
+    s->voices[i].freqHz    = hz;
+    s->voices[i].midiNote  = midiNote;
+    s->voices[i].targetAmp = 1.0f;
+    s->voices[i].phase     = 0.0f;
+    s->voices[i].active    = 1;
+}
+
+void synthNoteOff(Synth *s, int midiNote)
+{
+    for (int i = 0; i < VOICE_COUNT; i++) {
+        if (s->voices[i].active && s->voices[i].midiNote == midiNote)
+            s->voices[i].targetAmp = 0.0f;
+    }
+}
+
+void synthFillBuffer(Synth *s, int16_t *out, int frames)
+{
+    const float sr         = s->sampleRate;
+    const float attackInc  = (s->attackSec  <= 0.0f) ? 1.0f : (1.0f / (s->attackSec  * sr));
+    const float releaseInc = (s->releaseSec <= 0.0f) ? 1.0f : (1.0f / (s->releaseSec * sr));
+
+    for (int i = 0; i < frames; i++) {
+        float mix = 0.0f;
+
+        for (int v = 0; v < VOICE_COUNT; v++) {
+            Voice *vv = &s->voices[v];
+            if (!vv->active) continue;
+
+            if (vv->targetAmp > vv->amp) {
+                vv->amp += attackInc;
+                if (vv->amp > vv->targetAmp) vv->amp = vv->targetAmp;
+            } else if (vv->targetAmp < vv->amp) {
+                vv->amp -= releaseInc;
+                if (vv->amp < vv->targetAmp) vv->amp = vv->targetAmp;
+            }
+
+            if (vv->amp <= 0.0f && vv->targetAmp == 0.0f) {
+                vv->active = 0;
+                continue;
+            }
+
+            //vv->phase += vv->freqHz / sr;
+            float bendMultiplier = powf(2.0f, (s->pitchBend * s->pitchBendRange) / 12.0f);
+            vv->phase += (vv->freqHz * bendMultiplier) / sr;
+            if (vv->phase >= 1.0f) vv->phase -= 1.0f;
+
+            mix += waveformSample(s->waveform, vv->phase, s->dutyCycle) * vv->amp;
+        }
+
+        mix *= (0.2f / VOICE_COUNT) * 4.0f;
+
+        int32_t sample = (int32_t)lrintf(mix * 32767.0f);
+        if (sample >  32767) sample =  32767;
+        if (sample < -32768) sample = -32768;
+        out[i] = (int16_t)sample;
+    }
+}