Allow storing multiple buffers in a ALbufferlistitem

This will be to allow buffer layering, multiple buffers of the same format and
sample rate that are mixed together prior to resampling, filtering, and
panning. This will allow composing sounds from individual components that can
be swapped around on different invocations (e.g. layer SoundA and SoundB on one
instance and SoundA and SoundC on a different instance for a slightly different
sound, then just SoundA for a third instance, and so on). The longest buffer
within the list item determines the length of the list item.

More work needs to be done to fully support it, namely the ability to specity
multiple buffers to layer for static and streaming sources. Also the behavior
of loop points for layered static sources should be worked out. Should also
consider allowing each layer to have a sample offset.

2 files changed, 8 insertions, 4 deletions

diff --git a/Alc/ALu.c b/Alc/ALu.c
index 0da610d1..5f0c556a 100644
--- a/Alc/ALu.c
+++ b/Alc/ALu.c
@@ -1450,7 +1450,7 @@ static void CalcSourceParams(ALvoice *voice, ALCcontext *context, bool force)
     while(BufferListItem != NULL)
     {
         const ALbuffer *buffer;
-        if((buffer=BufferListItem->buffer) != NULL)
+        if(BufferListItem->num_buffers >= 1 && (buffer=BufferListItem->buffers[0]) != NULL)
         {
             if(props->SpatializeMode == SpatializeOn ||
                (props->SpatializeMode == SpatializeAuto && buffer->FmtChannels == FmtMono))
diff --git a/Alc/mixer.c b/Alc/mixer.c
index c77488bc..37bdf6ac 100644
--- a/Alc/mixer.c
+++ b/Alc/mixer.c
@@ -362,9 +362,13 @@ ALboolean MixSource(ALvoice *voice, ALsource *Source, ALCdevice *Device, ALsizei
             memcpy(SrcData, voice->PrevSamples[chan], MAX_PRE_SAMPLES*sizeof(ALfloat));
             SrcDataSize = MAX_PRE_SAMPLES;
 
+            /* TODO: Handle multi-buffer items by adding them together in
+             * SrcData. Need to work out how to deal with looping (loop
+             * points).
+             */
             if(isstatic)
             {
-                const ALbuffer *ALBuffer = BufferListItem->buffer;
+                const ALbuffer *ALBuffer = BufferListItem->buffers[0];
                 const ALubyte *Data = ALBuffer->data;
                 ALsizei DataSize;
 
@@ -421,7 +425,7 @@ ALboolean MixSource(ALvoice *voice, ALsource *Source, ALCdevice *Device, ALsizei
                 while(tmpiter && SrcBufferSize > SrcDataSize)
                 {
                     const ALbuffer *ALBuffer;
-                    if((ALBuffer=tmpiter->buffer) != NULL)
+                    if(tmpiter->num_buffers >= 1 && (ALBuffer=tmpiter->buffers[0]) != NULL)
                     {
                         const ALubyte *Data = ALBuffer->data;
                         ALsizei DataSize = ALBuffer->SampleLen;
@@ -637,7 +641,7 @@ ALboolean MixSource(ALvoice *voice, ALsource *Source, ALCdevice *Device, ALsizei
             ALsizei LoopStart = 0;
             ALsizei LoopEnd = 0;
 
-            if((ALBuffer=BufferListItem->buffer) != NULL)
+            if(BufferListItem->num_buffers >= 1 && (ALBuffer=BufferListItem->buffers[0]) != NULL)
             {
                 DataSize = ALBuffer->SampleLen;
                 LoopStart = ALBuffer->LoopStart;