SDL: Add SDL3 CD audio backend

Load playlist tracks through SDL3_mixer and play them on the shared
owner-aware music track. Preserve the CD-specific loop convention,
volume valancer, and playback position reporting.

src/CMakeLists.txt

@@ -117,6 +117,8 @@ endif()
 
 if (EMSCRIPTEN)
   target_sources(xsystem35 PRIVATE cdrom.emscripten.c)
+elseif (XSYSTEM35_SDL_VERSION STREQUAL "3")
+  target_sources(xsystem35 PRIVATE cdrom.sdl3mixer.c)
 else()
   target_sources(xsystem35 PRIVATE cdrom.mp3.c)
 endif()

src/cdrom.sdl3mixer.c

@@ -0,0 +1,201 @@
+/*
+ * cdrom.sdl3mixer.c  CD audio replacement using SDL3_mixer
+ *
+ * Copyright (C) 1997-1998 Masaki Chikama (Wren) <chikama@kasumi.ipl.mech.nagoya-u.ac.jp>
+ *               1998-                           <masaki-c@is.aist-nara.ac.jp>
+ *
+ * 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.
+ */
+
+#include "config.h"
+
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "ald_manager.h"
+#include "cdrom.h"
+#include "music_private.h"
+#include "sdl3_mixer_backend.h"
+#include "system.h"
+
+#define PLAYLIST_MAX 256
+
+static bool enabled;
+static char *playlist[PLAYLIST_MAX];
+static int track_no;
+static uint32_t start_time;
+
+static void cdrom_stop(void);
+
+static int clamp_volume(int volume)
+{
+	if (volume < 0)
+		return 0;
+	if (volume > 100)
+		return 100;
+	return volume;
+}
+
+static float music_gain(void)
+{
+	return clamp_volume(prv.volval[BGM_VOLVAL_CH]) / 100.0f;
+}
+
+static void apply_volume(void)
+{
+	sdl3_mixer_set_music_gain(SDL3_MIXER_MUSIC_CD, music_gain());
+}
+
+static void free_playlist(void)
+{
+	for (int track = 0; track < PLAYLIST_MAX; track++) {
+		free(playlist[track]);
+		playlist[track] = NULL;
+	}
+	prv.cd_maxtrk = 0;
+}
+
+static bool cdrom_init(char *playlist_path)
+{
+	if (!playlist_path || !playlist_path[0])
+		return false;
+
+	if (enabled)
+		cdrom_stop();
+	enabled = false;
+	free_playlist();
+	FILE *fp = fopen(playlist_path, "r");
+	char buf[256];
+	if (fp) {
+		/* The first line represents track 1, which is data on mixed CDs. */
+		fgets(buf, sizeof(buf), fp);
+	} else {
+		fp = fopen("_inmm.ini", "r");
+	}
+	if (!fp) {
+		if (ald_get_maxno(DRIFILE_MIDI) == 0)
+			NOTICE("cdrom: Cannot open playlist %s", playlist_path);
+		return false;
+	}
+
+	for (int track = 2; track < PLAYLIST_MAX; track++) {
+		if (!fgets(buf, sizeof(buf), fp))
+			break;
+		for (char *s = buf; *s; s++) {
+			if (*s == '\\')
+				*s = '/';
+			else if (*s == '\r' || *s == '\n') {
+				*s = '\0';
+				break;
+			}
+		}
+		if (*buf) {
+			playlist[track] = strdup(buf);
+			if (playlist[track])
+				prv.cd_maxtrk = track;
+		}
+	}
+	fclose(fp);
+	NOTICE("cdrom: Loaded playlist from %s", playlist_path);
+
+	track_no = 0;
+	enabled = true;
+	return true;
+}
+
+static void cdrom_exit(void)
+{
+	if (enabled)
+		cdrom_stop();
+	enabled = false;
+	free_playlist();
+}
+
+static void cdrom_reset(void)
+{
+	if (enabled)
+		cdrom_stop();
+}
+
+static bool cdrom_start(int track, int loop)
+{
+	if (!enabled || track < 0 || track >= PLAYLIST_MAX || !playlist[track])
+		return false;
+	cdrom_stop();
+
+	const char *path = playlist[track];
+#ifdef __ANDROID__
+	/* SDL's Android file IO requires an absolute path for installed tracks. */
+	char absolute_path[PATH_MAX];
+	if (!realpath(path, absolute_path))
+		return false;
+	path = absolute_path;
+#endif
+
+	MIX_Audio *audio = sdl3_mixer_load_music_file(path);
+	if (!audio) {
+		WARNING("Cannot load %s: %s", path, SDL_GetError());
+		return false;
+	}
+
+	/* CD playback passes loop directly; this differs from BGM's loop - 1. */
+	int loops = loop == 0 ? -1 : loop;
+	if (!sdl3_mixer_play_music(SDL3_MIXER_MUSIC_CD, audio,
+		loops, 0, music_gain()))
+		return false;
+
+	track_no = track;
+	start_time = sys_get_ticks();
+	return true;
+}
+
+static void cdrom_stop(void)
+{
+	if (!enabled)
+		return;
+	sdl3_mixer_stop_music(SDL3_MIXER_MUSIC_CD, 0);
+	track_no = 0;
+}
+
+static bool cdrom_get_playing_info(cd_time *info)
+{
+	if (!enabled || !track_no ||
+	    !sdl3_mixer_music_active(SDL3_MIXER_MUSIC_CD))
+		return false;
+
+	int ms = sys_get_ticks() - start_time;
+	info->t = track_no;
+	info->m = ms / (60 * 1000);
+	ms %= 60 * 1000;
+	info->s = ms / 1000;
+	ms %= 1000;
+	info->f = ms * CD_FPS / 1000;
+	return true;
+}
+
+static bool cdrom_is_available(void)
+{
+	return enabled;
+}
+
+static void cdrom_reapply_volume(void)
+{
+	if (enabled && track_no)
+		apply_volume();
+}
+
+cdromdevice_t cdrom_mp3 = {
+	.init = cdrom_init,
+	.exit = cdrom_exit,
+	.reset = cdrom_reset,
+	.start = cdrom_start,
+	.stop = cdrom_stop,
+	.getpos = cdrom_get_playing_info,
+	.is_available = cdrom_is_available,
+	.reapply_volume = cdrom_reapply_volume,
+};