(svn r2000) Split the sound system into backend (mixer.[ch]) and frontend (sound.[ch])

mixer.h

@@ -0,0 +1,24 @@
+#ifndef MIXER_H
+#define MIXER_H
+
+typedef struct Mixer Mixer;
+typedef struct MixerChannel MixerChannel;
+
+enum {
+	MX_AUTOFREE = 1,
+//	MX_8BIT = 2,
+//	MX_STEREO = 4,
+//	MX_UNSIGNED = 8,
+};
+
+VARDEF Mixer *_mixer;
+
+bool MxInitialize(uint rate);
+void MxMixSamples(Mixer *mx, void *buffer, uint samples);
+
+MixerChannel *MxAllocateChannel(Mixer *mx);
+void MxSetChannelRawSrc(MixerChannel *mc, int8 *mem, uint size, uint rate, uint flags);
+void MxSetChannelVolume(MixerChannel *mc, uint left, uint right);
+void MxActivate(MixerChannel*);
+
+#endif