filter: added "volume" plugin

The "volume" filter plugin will replace the current software volume
code.  One "volume" filter may be attached to each output device.
This will allow the user to use hardware mixers for some devices, and
software mixers for other devices at the same time.

Currently, neither the filter API nor the "volume" plugin is
integrated into MPD.

Makefile.am

@@ -194,6 +194,7 @@ src_mpd_SOURCES = \
 	src/filter_plugin.c \
 	src/filter_registry.c \
 	src/filter/null_filter_plugin.c \
+	src/filter/volume_filter_plugin.c \
 	src/update.c \
 	src/client.c \
 	src/listen.c \

src/filter/volume_filter_plugin.c

@@ -0,0 +1,136 @@
+/*
+ * Copyright (C) 2003-2009 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "filter_plugin.h"
+#include "filter_internal.h"
+#include "filter_registry.h"
+#include "conf.h"
+#include "pcm_buffer.h"
+#include "pcm_volume.h"
+#include "volume.h"
+#include "audio_format.h"
+
+#include <assert.h>
+#include <string.h>
+
+struct volume_filter {
+	struct filter filter;
+
+	struct audio_format audio_format;
+
+	struct pcm_buffer buffer;
+};
+
+static inline GQuark
+volume_quark(void)
+{
+	return g_quark_from_static_string("pcm_volume");
+}
+
+static struct filter *
+volume_filter_init(G_GNUC_UNUSED const struct config_param *param,
+		   G_GNUC_UNUSED GError **error_r)
+{
+	struct volume_filter *filter = g_new(struct volume_filter, 1);
+
+	filter_init(&filter->filter, &volume_filter_plugin);
+	return &filter->filter;
+}
+
+static void
+volume_filter_finish(struct filter *filter)
+{
+	g_free(filter);
+}
+
+static const struct audio_format *
+volume_filter_open(struct filter *_filter,
+		   const struct audio_format *audio_format,
+		   GError **error_r)
+{
+	struct volume_filter *filter = (struct volume_filter *)_filter;
+
+	if (audio_format->bits != 8 && audio_format->bits != 16 &&
+	    audio_format->bits != 24) {
+		g_set_error(error_r, volume_quark(), 0,
+			    "Unsupported audio format");
+		return false;
+	}
+
+	filter->audio_format = *audio_format;
+	pcm_buffer_init(&filter->buffer);
+
+	return &filter->audio_format;
+}
+
+static void
+volume_filter_close(struct filter *_filter)
+{
+	struct volume_filter *filter = (struct volume_filter *)_filter;
+
+	pcm_buffer_deinit(&filter->buffer);
+}
+
+static const void *
+volume_filter_filter(struct filter *_filter, const void *src, size_t src_size,
+		     size_t *dest_size_r, GError **error_r)
+{
+	struct volume_filter *filter = (struct volume_filter *)_filter;
+	int volume;
+	bool success;
+	void *dest;
+
+	volume = volume_level_get(); /* XXX don't use volume_level_get() */
+	if (volume < 0 || volume >= PCM_VOLUME_1) {
+		/* optimized special case: 100% volume = no-op */
+		*dest_size_r = src_size;
+		return src;
+	}
+
+	dest = pcm_buffer_get(&filter->buffer, src_size);
+	*dest_size_r = src_size;
+
+	if (volume == 0) {
+		/* optimized special case: 0% volume = memset(0) */
+		/* XXX is this valid for all sample formats? What
+		   about floating point? */
+		memset(dest, 0, src_size);
+		return dest;
+	}
+
+	memcpy(dest, src, src_size);
+
+	success = pcm_volume(dest, src_size, &filter->audio_format, volume);
+	if (!success) {
+		g_set_error(error_r, volume_quark(), 0,
+			    "pcm_volume() has failed");
+		return NULL;
+	}
+
+	return dest;
+}
+
+const struct filter_plugin volume_filter_plugin = {
+	.name = "volume",
+	.init = volume_filter_init,
+	.finish = volume_filter_finish,
+	.open = volume_filter_open,
+	.close = volume_filter_close,
+	.filter = volume_filter_filter,
+};

src/filter_registry.c

@@ -25,6 +25,7 @@
 
 const struct filter_plugin *const filter_plugins[] = {
 	&null_filter_plugin,
+	&volume_filter_plugin,
 	NULL,
 };
 

src/filter_registry.h

@@ -27,6 +27,7 @@
 #define MPD_FILTER_REGISTRY_H
 
 extern const struct filter_plugin null_filter_plugin;
+extern const struct filter_plugin volume_filter_plugin;
 
 const struct filter_plugin *
 filter_plugin_by_name(const char *name);