From dfbffd8cafc7b249e08d022d5b47e7e5f25546fd Mon Sep 17 00:00:00 2001
From: Joshua Phillips <jp.sittingduck@gmail.com>
Date: Sun, 28 Dec 2008 19:53:22 +0000
Subject: [PATCH] Simple ring modulator (silly_effect)

---
 SConscript |  3 ++-
 effect.h   | 14 ++++++++++++++
 effects.c  | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 effects.h  |  9 +++++++++
 main.c     |  6 ++++++
 5 files changed, 77 insertions(+), 1 deletion(-)
 create mode 100644 effect.h
 create mode 100644 effects.c
 create mode 100644 effects.h

diff --git a/SConscript b/SConscript
index ff98143..a0b86d8 100644
--- a/SConscript
+++ b/SConscript
@@ -2,7 +2,8 @@ import os.path
 Import(['env'])
 
 programs = {
-    'main': ['main.c', 'wavefile.c', 'soundout.c', 'aformat.c', 'sound-ioctl.c'],
+    'main': [   'main.c', 'wavefile.c', 'soundout.c', 'aformat.c', 'sound-ioctl.c',
+                'effects.c'],
 }
 
 objects = {}
diff --git a/effect.h b/effect.h
new file mode 100644
index 0000000..40b0889
--- /dev/null
+++ b/effect.h
@@ -0,0 +1,14 @@
+#ifndef EFFECT_H
+#define EFFECT_H
+
+struct effect;
+
+struct effect_vtab {
+    int (* process)(struct effect *ef, void **buf, long n_samples);
+};
+
+struct effect {
+    const struct effect_vtab *vtab;
+};
+
+#endif
diff --git a/effects.c b/effects.c
new file mode 100644
index 0000000..2ac9edf
--- /dev/null
+++ b/effects.c
@@ -0,0 +1,46 @@
+#include "effects.h"
+#include "effect.h"
+#include "math.h"
+#include "stdlib.h"
+
+struct silly_effect {
+    struct effect e;
+};
+
+int silly_effect_process(struct effect *ef, void **buf, long n_samples)
+{
+    short *bufp;
+    int i;
+
+    if (!*buf){
+        // we're not a source
+        return 1;
+    }
+
+    bufp = *buf;
+    for (i = 0; i < n_samples; ++i){
+        bufp[i * 2] *= cos((i * 2 * M_PI) / 441.0);
+        bufp[i * 2 + 1] *= cos((i * 2 * M_PI) / 441.0);
+    }
+    return 0;
+}
+
+static const struct effect_vtab silly_effect_vtab = {
+    process: silly_effect_process,
+};
+
+struct effect *silly_effect_create(void)
+{
+    struct silly_effect *se;
+    se = malloc(sizeof *se);
+    if (!se){
+        return NULL;
+    }
+    se->e.vtab = &silly_effect_vtab;
+    return &se->e;
+}
+
+void silly_effect_free(struct effect *e)
+{
+    free(e);
+}
diff --git a/effects.h b/effects.h
new file mode 100644
index 0000000..344a465
--- /dev/null
+++ b/effects.h
@@ -0,0 +1,9 @@
+#ifndef EFFECTS_H
+#define EFFECTS_H
+
+#include "effect.h"
+
+struct effect *silly_effect_create(void);
+void silly_effect_free(struct effect *e);
+
+#endif
diff --git a/main.c b/main.c
index 8f9045b..ed6236e 100644
--- a/main.c
+++ b/main.c
@@ -1,12 +1,14 @@
 #include "stdio.h"
 #include "soundout.h"
 #include "wavefile.h"
+#include "effects.h"
 
 int main(int argc, char **argv)
 {
     struct soundout so;
     struct wavefile wf;
     struct aformat af;
+    struct effect *ef1;
 
     if (wavefile_open(&wf, "/home/aoe/reflections.wav") != 0){
         fprintf(stderr, "cannot open wave file\n");
@@ -23,13 +25,17 @@ int main(int argc, char **argv)
         return 1;
     }
 
+    ef1 = silly_effect_create();
+
     unsigned int pos = 0;
     char buf[4410 * 4];
+    void *buf_ptr = buf;
     for (;;){
         if (wavefile_read_at(&wf, pos, buf, 4410) != 0){
             // end of file
             break;
         }
+        ef1->vtab->process(ef1, &buf_ptr, 4410);
         soundout_write(&so, buf, 4410 * 4);
         pos += 4410;
     }
-- 
2.11.4.GIT