From 8bacb5dfb8ef910586fcf5b5cd89526ec81061e8 Mon Sep 17 00:00:00 2001
From: Chris Robinson <chris.kcat@gmail.com>
Date: Sun, 16 Sep 2018 17:38:55 -0700
Subject: [PATCH] Fix buffer queue mixing logic

In particular, the source sample position was reduced by the size of the
next buffer list item when one is completed, rather than the size of the
one it just completed.
---
 Alc/mixvoice.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/Alc/mixvoice.c b/Alc/mixvoice.c
index 2d935ce5..276d5bd9 100644
--- a/Alc/mixvoice.c
+++ b/Alc/mixvoice.c
@@ -487,6 +487,7 @@ ALboolean MixSource(ALvoice *voice, ALuint SourceID, ALCcontext *Context, ALsize
                 while(tmpiter && SrcBufferSize > FilledAmt)
                 {
                     ALsizei SizeToDo = SrcBufferSize - FilledAmt;
+                    ALsizei CompLen = 0;
                     ALsizei i;
 
                     for(i = 0;i < tmpiter->num_buffers;i++)
@@ -499,23 +500,24 @@ ALboolean MixSource(ALvoice *voice, ALuint SourceID, ALCcontext *Context, ALsize
                             const ALubyte *Data = ALBuffer->data;
                             Data += (pos*NumChannels + chan)*SampleSize;
 
-                            DataSize = minu(SizeToDo, DataSize - pos);
+                            DataSize = mini(SizeToDo, DataSize - pos);
+                            CompLen = maxi(CompLen, DataSize);
+
                             LoadSamples(&SrcData[FilledAmt], Data, NumChannels,
                                         ALBuffer->FmtType, DataSize);
                         }
                     }
-                    if(pos > tmpiter->max_samples)
+                    if(UNLIKELY(!CompLen))
                         pos -= tmpiter->max_samples;
                     else
                     {
-                        FilledAmt += tmpiter->max_samples - pos;
+                        FilledAmt += CompLen;
+                        if(SrcBufferSize <= FilledAmt)
+                            break;
                         pos = 0;
                     }
-                    if(SrcBufferSize > FilledAmt)
-                    {
-                        tmpiter = ATOMIC_LOAD(&tmpiter->next, almemory_order_acquire);
-                        if(!tmpiter) tmpiter = BufferLoopItem;
-                    }
+                    tmpiter = ATOMIC_LOAD(&tmpiter->next, almemory_order_acquire);
+                    if(!tmpiter) tmpiter = BufferLoopItem;
                 }
             }
 
@@ -729,8 +731,10 @@ ALboolean MixSource(ALvoice *voice, ALuint SourceID, ALCcontext *Context, ALsize
             if(BufferListItem->max_samples > DataPosInt)
                 break;
 
+            DataPosInt -= BufferListItem->max_samples;
+
             buffers_done += BufferListItem->num_buffers;
-            BufferListItem = ATOMIC_LOAD(&BufferListItem->next, almemory_order_acquire);
+            BufferListItem = ATOMIC_LOAD(&BufferListItem->next, almemory_order_relaxed);
             if(!BufferListItem && !(BufferListItem=BufferLoopItem))
             {
                 isplaying = false;
@@ -738,8 +742,6 @@ ALboolean MixSource(ALvoice *voice, ALuint SourceID, ALCcontext *Context, ALsize
                 DataPosFrac = 0;
                 break;
             }
-
-            DataPosInt -= BufferListItem->max_samples;
         }
     } while(isplaying && OutPos < SamplesToDo);