let SDL_Mixer do the actual sound mixing (#43)

* add a dummy fx_mixer.c template

* let SDL_Mixer do the actual sound mixing

* fixes

* more fixes

* next fix

* add a SDL_Mixer version guard

* provide an alternative per-channel FX_SetVolume() implementation for SDL_Mixer < 2.6.0

* cosmetics

* immediately stop music on Windows in CP_Quit()

Instead of fading it out, that is, because on Windows changing the music
channel volume affects the sfx channels as well. Fixes #8

configure.ac

@@ -88,5 +88,5 @@ AC_ARG_ENABLE([werror],
 AS_IF([test "x$enable_werror" = "xyes"],
       [CFLAGS="$CFLAGS -Werror"])
 
-AC_CONFIG_FILES([Makefile rott/Makefile rott/audiolib/Makefile])
+AC_CONFIG_FILES([Makefile rott/Makefile])
 AC_OUTPUT

rott/Makefile.am

@@ -1,5 +1,3 @@
-SUBDIRS = audiolib
-
 bin_PROGRAMS = rott@SUFFIX@
 rott@SUFFIX@_SOURCES = \
 	byteordr.c \
@@ -12,6 +10,7 @@ rott@SUFFIX@_SOURCES = \
 	dosutil.c \
 	dukemusc.c \
 	engine.c \
+	fx_mixer.c \
 	isr.c \
 	m_misc2.c \
 	modexlib.c \
@@ -53,4 +52,4 @@ rott@SUFFIX@_SOURCES = \
 	w_wad.c \
 	z_zone.c
 rott@SUFFIX@_CFLAGS = @SDL_CFLAGS@ @SDL_mixer_CFLAGS@
-rott@SUFFIX@_LDADD = audiolib/libaudiolib.a @SDL_LIBS@ @SDL_mixer_LIBS@
+rott@SUFFIX@_LDADD = @SDL_LIBS@ @SDL_mixer_LIBS@

rott/_rt_soun.h

@@ -30,6 +30,7 @@ typedef struct
    byte    count;
    int     prevhandle;
    int     prevdistance;
+   void   *chunk;
 } sound_t;
 
 #define SD_OVERWRITE  0x01