1 files changed, 164 insertions, 0 deletions
diff --git a/mod/gain.c b/mod/gain.c
new file mode 100644
index 0000000..994efcf
--- /dev/null
+++ b/mod/gain.c
@@ -0,0 +1,164 @@
+/*
+ * melisma - extensible and scriptable audio engine
+ * Copyright (C) 2026  Ludvig Gunne Lindström
+ *
+ * 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 3 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, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <string.h>
+#include <stdlib.h>
+#include <math.h>
+
+#include <lauxlib.h>
+
+#include "melisma.h"
+#include "mutil.h"
+
+#define GAIN_TYPENAME "gain"
+
+struct gain
+{
+	ml_node *node;
+	float    value;
+	int      mapped;
+	int      db;
+};
+
+static void proc(const ml_proc_args *args)
+{
+	struct gain *gain = args->userp;
+
+	float *in = args->in[0];
+	float *out = args->out[0];
+	float *mapped = gain->mapped ? args->in[1] :  NULL;
+	float v;
+
+	for (size_t i = 0; i < args->nframes; i++)
+	{
+		v = mapped ? mapped[i] : gain->value;
+
+		if (gain->db)
+		{
+			v = powf(10,v/20.f);
+		}
+
+		out[i] = v*in[i];
+	}
+}
+
+static int l_init(lua_State *s)
+{
+	int db_i = lua_upvalueindex(1);
+	int db = lua_tointeger(s,db_i);
+	ml_channel *audio_src, *mapped_src = NULL;
+	ml_channel *audio_dst, *mapped_dst;
+	float value = 0;
+
+
+	if (lua_isuserdata(s,1))
+	{
+		mapped_src = mutil_get_channel(s,1);
+	}
+	else
+	{
+		value = luaL_checknumber(s,1);
+	}
+
+	audio_src = mutil_get_channel(s,2);
+
+	struct gain *gain = calloc(1,sizeof(*gain));
+	gain->value = value;
+	gain->mapped = mapped_src != NULL;
+	gain->db = db;
+
+	ml_node *node = ml_create_node(proc,gain);
+	ml_label_node(node,"gain");
+	gain->node = node;
+
+	ml_add_output(node);
+
+	audio_dst = ml_add_input(node);
+	ml_connect(audio_src,audio_dst);
+
+	if (mapped_src)
+	{
+		mapped_dst = ml_add_input(node);
+		ml_connect(mapped_src,mapped_dst);
+	}
+
+	*(void**) lua_newuserdata(s,sizeof(void*)) = gain;
+	luaL_setmetatable(s,GAIN_TYPENAME);
+
+	return 1;
+}
+
+static int l_out(lua_State *s)
+{
+	struct gain *gain = *(void**) luaL_checkudata(s,1,GAIN_TYPENAME);
+	*(void**) lua_newuserdata(s,sizeof(void*)) = ml_get_output(gain->node,0);
+	luaL_setmetatable(s,MELISMA_OUTPUT_CHANNEL_TYPENAME);
+	return 1;
+}
+
+int luaopen_melisma_gain(lua_State *s)
+{
+	ml_check_version();
+
+/*** Apply gain to signals.
+	local mgain = require 'melisma.gain'
+
+	-- Interprets `cntl` as decibels and applies it to `input`
+	local input = ...
+	local cntl = ...
+	local gain = mgain.db(input,cntl)
+
+@classmod gain
+*/
+	lua_newtable(s);
+	int tbl = lua_gettop(s);
+
+/*** Creates a linear gain unit.
+@static
+@function linear
+@tparam channel input Input signal.
+@tparam number|channel gain Constant gain or a controlling signal.
+@treturn gain The newly created gain unit.
+*/
+	lua_pushinteger(s,0);
+	lua_pushcclosure(s,l_init,1);
+	lua_setfield(s,tbl,"linear");
+
+/*** Creates a decibel gain unit.
+@static
+@function db
+@tparam channel input Input signal.
+@tparam number|channel gain Constant gain in decibels or a controlling signal.
+@treturn gain The newly created gain unit.
+*/
+	lua_pushinteger(s,1);
+	lua_pushcclosure(s,l_init,1);
+	lua_setfield(s,tbl,"db");
+
+	lua_pushcfunction(s,l_out);
+	lua_setfield(s,tbl,MUTIL_OUTPUT_CHANNEL_FUNCTION);
+
+	luaL_newmetatable(s,GAIN_TYPENAME);
+	int mt = lua_gettop(s);
+
+	lua_pushvalue(s,tbl);
+	lua_setfield(s,mt,"__index");
+
+	lua_settop(s,tbl);
+	return 1;
+}