first delay effect

delay.c

@@ -0,0 +1,32 @@
+#include <stdint.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include "delay.h"
+
+void delay_init(
+    struct delay * delay
+) {
+    delay->duration = 15000;
+    delay->mix = 0.8;
+    delay->feedback = 0.6;
+
+    delay->buf_idx = 0;
+    delay->buf = calloc( delay->duration, sizeof(float) );
+}
+
+void delay_process(
+    struct delay * delay,
+    size_t frame_size,
+    float const * in,
+    float * out
+) {
+    for( size_t i = 0; i < frame_size; ++i ) {
+        out[i] =
+            (1.0 - delay->mix) * in[i]
+            + delay->mix * delay->buf[ delay->buf_idx ];
+
+        delay->buf[ delay->buf_idx ] *= delay->feedback;
+        delay->buf[ delay->buf_idx ] += (1.0 - delay->feedback) * in[i];
+        delay->buf_idx = (delay->buf_idx + 1) % delay->duration;
+    }
+}

delay.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <stdint.h>
+#include <stddef.h>
+
+struct delay {
+    uint64_t duration;
+    float feedback;
+    float mix;
+
+    uint64_t buf_idx;
+    float * buf;
+};
+
+void delay_init(
+    struct delay * delay
+);
+
+void delay_process(
+    struct delay * delay,
+    size_t frame_size,
+    float const * in,
+    float * out
+);

guitfx.c

@@ -13,6 +13,8 @@
 #include <pipewire/pipewire.h>
 #include <pipewire/filter.h>
 
+#include "delay.h"
+
 struct data;
 
 struct port {
@@ -26,6 +28,9 @@ struct data {
 	struct port * midi_in_port;
 	struct port * out_port;
 
+	//! effect data
+	struct delay delay;
+
 	//! elapsed time in number of samples
 	uint64_t time;
 };
@@ -33,13 +38,11 @@ struct data {
 static void on_process(void *userdata, struct spa_io_position *position)
 {
 	struct data *data = userdata;
-	float *in, *out;
+
 	uint32_t n_samples = position->clock.duration;
 	uint64_t frame = data->time;
 	data->time += n_samples;
 
-	//printf("do process (%d samples) at %u\n", n_samples, frame);
-
 	struct pw_buffer * b = pw_filter_dequeue_buffer(data->midi_in_port);
 	if( b == NULL ) {
 	   fprintf(stderr, "on_process(): no buffer for midi_in_port\n");
@@ -89,11 +92,10 @@ static void on_process(void *userdata, struct spa_io_position *position)
 	pw_filter_queue_buffer(data->midi_in_port, b);
 
 
-	in = pw_filter_get_dsp_buffer(data->guit_in_port, n_samples);
-	out = pw_filter_get_dsp_buffer(data->out_port, n_samples);
-
+	float * const in = pw_filter_get_dsp_buffer(data->guit_in_port, n_samples);
+	float * out = pw_filter_get_dsp_buffer(data->out_port, n_samples);
 	if( in && out ) {
-	   memcpy(out, in, n_samples * sizeof(float));
+        delay_process( &data->delay, n_samples, in, out );
 	}
 }
 
@@ -111,6 +113,9 @@ static void do_quit(void *userdata, int signal_number)
 int main(int argc, char *argv[])
 {
 	struct data data = { 0, };
+
+	delay_init( &data.delay );
+
 	const struct spa_pod *params[1];
 	uint8_t buffer[1024];
 	struct spa_pod_builder b = SPA_POD_BUILDER_INIT(buffer, sizeof(buffer));

meson.build

@@ -3,5 +3,6 @@ pipewire_dep = dependency('libpipewire-0.3')
 executable(
     'guitfx',
     'guitfx.c',
+    'delay.c',
     dependencies : [pipewire_dep],
 )