1 files changed, 281 insertions, 0 deletions
diff --git a/mod/buffer.c b/mod/buffer.c
new file mode 100644
index 0000000..64ba13e
--- /dev/null
+++ b/mod/buffer.c
@@ -0,0 +1,281 @@
+/*
+ * 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 <stdlib.h>
+#include <string.h>
+#include <lauxlib.h>
+#include "melisma.h"
+#include "mutil.h"
+
+#define BUFFER_TYPENAME "buffer"
+
+enum mode {CAPTURE,PLAYBACK,IDLE};
+
+struct buffer
+{
+	ml_channel *chan;
+	enum mode   mode;
+	double      phase;
+	double      speed;
+	size_t      len;
+	size_t      cap;
+	float       data[];
+};
+
+static size_t capture(struct buffer *b, const float *in, size_t n)
+{
+	size_t i = 0;
+
+	for (; i < n; i++)
+	{
+		b->data[b->len++] = in[i];
+
+		if (b->len == b->cap)
+		{
+			b->mode = IDLE;
+			b->phase = 0;
+			break;
+		}
+	}
+
+	return i;
+}
+
+static size_t playback(struct buffer *b, float *out, size_t n)
+{
+	size_t i = 0;
+
+	for (; i < n; i++)
+	{
+		float t = b->phase*b->len;
+		size_t i0 = (size_t) t;
+		size_t i1 = i0 + 1;
+		float ip = t - i0;
+
+		i0 %= b->len;
+		i1 %= b->len;
+
+		float s0 = b->data[i0];
+		float s1 = b->data[i1];
+
+		out[i] = s0 + ip*(s1 - s0);
+
+		b->phase += b->speed/b->len;
+
+		if (b->phase >= 1)
+		{
+			b->phase = 0;
+			b->mode = IDLE;
+		}
+	}
+
+	return i;
+}
+
+static size_t idle(struct buffer *b, float *out, size_t n)
+{
+	memset(out,0,sizeof(*out)*n);
+	return n;
+}
+
+static void proc(const ml_proc_args *args)
+{
+	struct buffer *b = args->userp;
+	const float *in = args->in[0];
+	float *out = args->out[0];
+	size_t n = args->nframes;
+
+	while (n > 0)
+	{
+		size_t d;
+
+		switch (b->mode)
+		{
+		case CAPTURE:
+			d = capture(b,in,n);
+			break;
+		case PLAYBACK:
+			d = playback(b,out,n);
+			break;
+		case IDLE:
+			d = idle(b,out,n);
+			break;
+		}
+
+		in += d;
+		out += d;
+		n -= d;
+	}
+}
+
+static int l_init(lua_State *s)
+{
+	float t = luaL_checknumber(s,1);
+	ml_channel *src = mutil_get_channel(s,2);
+
+	if (t <= 0)
+	{
+		luaL_error(s,"invalid buffer capacity %.2f\n",t);
+	}
+
+	size_t sr = ml_sample_rate();
+	size_t cap = t*sr;
+
+	struct buffer *b;
+	size_t size = sizeof(*b) + sizeof(*b->data)*cap;
+	b = calloc(1,size);
+
+	ml_node *node = ml_create_node(proc,b);
+	ml_label_node(node,"buffer");
+
+	ml_channel *dst = ml_add_input(node);
+	ml_connect(src,dst);
+
+	b->mode = IDLE;
+	b->len  = 0;
+	b->phase = 0;
+	b->cap  = cap;
+	b->chan = ml_add_output(node);
+
+	*(void**) lua_newuserdata(s,sizeof(void*)) = b;
+	luaL_setmetatable(s,BUFFER_TYPENAME);
+
+	return 1;
+}
+
+static int l_setmode(lua_State *s)
+{
+	int mode_i = lua_upvalueindex(1);
+	struct buffer *b = *(void**) luaL_checkudata(s,1,BUFFER_TYPENAME);
+	enum mode mode = lua_tointeger(s,mode_i);
+	b->phase = 0;
+	b->mode = mode;
+
+	if (mode == CAPTURE)
+	{
+		b->len = 0;
+	}
+
+	return 0;
+}
+
+static int l_setspeed(lua_State *s)
+{
+	struct buffer *b = *(void**) luaL_checkudata(s,1,BUFFER_TYPENAME);
+	double speed = luaL_checknumber(s,2);
+
+	if (speed <= 0)
+	{
+		luaL_error(s,"invalid speed %.2f",speed);
+	}
+
+	b->speed = speed;
+	return 0;
+}
+
+static int l_getlength(lua_State *s)
+{
+	struct buffer *b = *(void**) luaL_checkudata(s,1,BUFFER_TYPENAME);
+	size_t sr = ml_sample_rate();
+	lua_pushnumber(s,(float)b->len / (float)sr / b->speed);
+	return 1;
+}
+
+static int l_out(lua_State *s)
+{
+	struct buffer *b = *(void**) luaL_checkudata(s,1,BUFFER_TYPENAME);
+	*(void**) lua_newuserdata(s,sizeof(void*)) = b->chan;
+	luaL_setmetatable(s,MELISMA_OUTPUT_CHANNEL_TYPENAME);
+	return 1;
+}
+
+int luaopen_melisma_buffer(lua_State *s)
+{
+/*** Audio buffer for capture/playback.
+
+	local mbuffer = require 'melisma.buffer'
+	local mevent = require 'melisma.event'
+
+	local input = ...
+
+	-- Create a buffer with capacity of 5 seconds
+	-- Capture stops automatically when buffer is full.
+	local len = 5
+	local buffer = mbuffer.init(input, len)
+
+	-- Capture audio
+	buffer:capture()
+
+	-- Playback after capture 3 seconds
+	mevent.schedule(3, buffer.playback, buffer)
+
+@classmod buffer
+*/
+	lua_newtable(s);
+	int tbl = lua_absindex(s,lua_gettop(s));
+
+/*** Create an audio buffer.
+@static
+@function buffer.init
+@tparam channel input Input signal.
+@tparam number len Buffer capacity in seconds.
+@treturn buffer The newly created audio buffer.
+*/
+	lua_pushcfunction(s,l_init);
+	lua_setfield(s,tbl,"init");
+
+/*** Set playback speed.
+@function buffer.speed
+@tparam number speed Playback speed.
+*/
+	lua_pushcfunction(s,l_setspeed);
+	lua_setfield(s,tbl,"speed");
+
+/*** Get length of captured audio.
+@function buffer.length
+@treturn number Length of captured audio in seconds.
+*/
+	lua_pushcfunction(s,l_getlength);
+	lua_setfield(s,tbl,"length");
+
+/*** Start playback mode.
+@function buffer.playback
+*/
+	lua_pushinteger(s,PLAYBACK);
+	lua_pushcclosure(s,l_setmode,1);
+	lua_setfield(s,tbl,"playback");
+
+/*** Start capture mode.
+@function buffer.capture
+*/
+	lua_pushinteger(s,CAPTURE);
+	lua_pushcclosure(s,l_setmode,1);
+	lua_setfield(s,tbl,"capture");
+
+	lua_pushcfunction(s,l_out);
+	lua_setfield(s,tbl,MUTIL_OUTPUT_CHANNEL_FUNCTION);
+
+	luaL_newmetatable(s,BUFFER_TYPENAME);
+	int mt = lua_absindex(s,lua_gettop(s));
+
+	lua_pushvalue(s,tbl);
+	lua_setfield(s,mt,"__index");
+
+	lua_settop(s,tbl);
+	return 1;
+}