From 1bbe0659cfc4f1ea17e2c05869578959cc11fdfc Mon Sep 17 00:00:00 2001
From: XANTRONIX Development
Date: Tue, 15 Mar 2022 17:45:12 -0400
Subject: Implement polyphonic synth streams

Implement polyphonic synth streams by allowing one to create a new audio
source passing multiple streams at once, wherein each synth is sampled
and merged with the final stream output
---
 include/xas/synth.h |  3 ++
 src/synth.c         | 89 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 92 insertions(+)

diff --git a/include/xas/synth.h b/include/xas/synth.h
index 7ec4af4..e513f2a 100644
--- a/include/xas/synth.h
+++ b/include/xas/synth.h
@@ -65,4 +65,7 @@ void xas_synth_stop(xas_synth *synth);
 
 xas_audio_stream *xas_synth_stream_new(xas_synth *synth);
 
+xas_audio_stream *xas_synth_stream_new_poly(xas_synth **synths,
+                                                size_t count);
+
 #endif /* _XAS_SYNTH_H */
diff --git a/src/synth.c b/src/synth.c
index 596539f..56bbe5b 100644
--- a/src/synth.c
+++ b/src/synth.c
@@ -4,6 +4,11 @@
 
 #include <xas/synth.h>
 
+struct poly {
+    xas_synth **synths;
+    size_t count;
+};
+
 static int16_t sample_sine(xas_synth *synth) {
     int16_t ret;
     static float tau = 2.0f * M_PI;
@@ -220,3 +225,87 @@ xas_audio_stream *xas_synth_stream_new(xas_synth *synth) {
                                           synth->buffer_size,
                                           synth);
 }
+
+static ssize_t poly_fill(struct poly *poly, int16_t *samples, size_t count) {
+    size_t s;
+
+    for (s=0; s<count; s++) {
+        samples[s] = 0;
+
+        size_t i;
+
+        for (i=0; i<poly->count; i++) {
+            xas_synth *synth = poly->synths[i];
+
+            samples[s] += synth->sample(synth);
+        }
+    }
+
+    return count;
+}
+
+static void poly_cleanup(struct poly *poly) {
+    free(poly->synths);
+    free(poly);
+}
+
+xas_audio_stream *xas_synth_stream_new_poly(xas_synth **synths,
+                                                size_t count) {
+    struct poly *poly;
+    size_t i;
+
+    xas_audio_format format;
+    size_t buffer_size;
+
+    if (count == 0) {
+        errno = EINVAL;
+
+        goto error_invalid_count;
+    }
+
+    format      = synths[0]->format;
+    buffer_size = synths[0]->buffer_size;
+
+    if ((poly = malloc(sizeof(*poly))) == NULL) {
+        goto error_malloc_poly;
+    }
+
+    if ((poly->synths = malloc(count * sizeof(xas_synth *))) == NULL) {
+        goto error_malloc_synths;
+    }
+
+    for (i=0; i<count; i++) {
+        if (!xas_audio_format_eq(synths[i]->format, format)) {
+            errno = EINVAL;
+
+            goto error_invalid_format;
+        }
+
+        if (synths[i]->buffer_size != buffer_size) {
+            errno = EINVAL;
+
+            goto error_invalid_buffer_size;
+        }
+
+        poly->synths[i] = synths[i];
+    }
+
+    poly->count = count;
+
+    return xas_audio_stream_new_source((xas_audio_fill)poly_fill,
+                                         (xas_audio_cleanup)poly_cleanup,
+                                         format,
+                                         buffer_size,
+                                         poly);
+
+error_invalid_buffer_size:
+error_invalid_format:
+    free(poly->synths);
+
+error_malloc_synths:
+    free(poly);
+
+error_malloc_poly:
+error_invalid_count:
+    return NULL;
+}
-- 
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