From 03389f390c2b9979563b0901bdb73b2e0cd0e8fb Mon Sep 17 00:00:00 2001
From: Chris Robinson <chris.kcat@gmail.com>
Date: Mon, 2 Nov 2020 05:08:23 -0800
Subject: [PATCH] Avoid a full wipe and reallocation of wet buffers

---
 alc/alc.cpp     | 28 ++++++----------------------
 alc/panning.cpp | 45 ++++++++++++++++++++++++++++++++++-----------
 2 files changed, 40 insertions(+), 33 deletions(-)

diff --git a/alc/alc.cpp b/alc/alc.cpp
index b3da9209..c94a9d53 100644
--- a/alc/alc.cpp
+++ b/alc/alc.cpp
@@ -2102,29 +2102,13 @@ static ALCenum UpdateDeviceParams(ALCdevice *device, const int *attrList)
     {
         std::unique_lock<std::mutex> proplock{context->mPropLock};
         std::unique_lock<std::mutex> slotlock{context->mEffectSlotLock};
-        /* HACK: Clear the effect slots' wet buffer references, and clear the wet
-         * buffer array so they're reallocated (with potentially a new channel
-         * count) when reinitialized.
-         */
-        if(ALeffectslot *slot{context->mDefaultSlot.get()})
-        {
-            slot->mWetBuffer = nullptr;
-            slot->Wet.Buffer = {};
-        }
-        for(auto &sublist : context->mEffectSlotList)
-        {
-            uint64_t usemask{~sublist.FreeMask};
-            while(usemask)
-            {
-                const ALsizei idx{CountTrailingZeros(usemask)};
-                ALeffectslot *slot{sublist.EffectSlots + idx};
-                usemask &= ~(1_u64 << idx);
 
-                slot->mWetBuffer = nullptr;
-                slot->Wet.Buffer = {};
-            }
-        }
-        decltype(context->mWetBuffers){}.swap(context->mWetBuffers);
+        /* Clear out unused wet buffers. */
+        auto buffer_not_in_use = [](WetBufferPtr &wetbuffer) noexcept -> bool
+        { return !wetbuffer->mInUse; };
+        auto wetbuffer_iter = std::remove_if(context->mWetBuffers.begin(),
+            context->mWetBuffers.end(), buffer_not_in_use);
+        context->mWetBuffers.erase(wetbuffer_iter, context->mWetBuffers.end());
 
         if(ALeffectslot *slot{context->mDefaultSlot.get()})
         {
diff --git a/alc/panning.cpp b/alc/panning.cpp
index ee7f39eb..51c13771 100644
--- a/alc/panning.cpp
+++ b/alc/panning.cpp
@@ -1040,20 +1040,43 @@ void aluInitEffectPanning(ALeffectslot *slot, ALCcontext *context)
     ALCdevice *device{context->mDevice.get()};
     const size_t count{AmbiChannelsFromOrder(device->mAmbiOrder)};
 
-    ALuint idx{0};
-    for(auto &wetbuffer : context->mWetBuffers)
+    auto wetbuffer_iter = context->mWetBuffers.end();
+    if(slot->mWetBuffer)
     {
-        if(!wetbuffer->mInUse)
-            break;
-        ++idx;
+        /* If the effect slot already has a wet buffer attached, allocate a new
+         * one in its place.
+         */
+        wetbuffer_iter = context->mWetBuffers.begin();
+        for(;wetbuffer_iter != context->mWetBuffers.end();++wetbuffer_iter)
+        {
+            if(wetbuffer_iter->get() == slot->mWetBuffer)
+            {
+                slot->mWetBuffer = nullptr;
+                slot->Wet.Buffer = {};
+
+                *wetbuffer_iter = WetBufferPtr{new(FamCount(count)) WetBuffer{count}};
+
+                break;
+            }
+        }
     }
-    if(idx == context->mWetBuffers.size())
+    if(wetbuffer_iter == context->mWetBuffers.end())
     {
-        auto newbuffer = WetBufferPtr{new(FamCount(count)) WetBuffer{count}};
-        context->mWetBuffers.emplace_back(std::move(newbuffer));
+        /* Otherwise, search for an unused wet buffer. */
+        wetbuffer_iter = context->mWetBuffers.begin();
+        for(;wetbuffer_iter != context->mWetBuffers.end();++wetbuffer_iter)
+        {
+            if(!(*wetbuffer_iter)->mInUse)
+                break;
+        }
+        if(wetbuffer_iter == context->mWetBuffers.end())
+        {
+            /* Otherwise, allocate a new one to use. */
+            context->mWetBuffers.emplace_back(WetBufferPtr{new(FamCount(count)) WetBuffer{count}});
+            wetbuffer_iter = context->mWetBuffers.end()-1;
+        }
     }
-    auto *wetbuffer = context->mWetBuffers[idx].get();
-    slot->mWetBuffer = wetbuffer;
+    WetBuffer *wetbuffer{slot->mWetBuffer = wetbuffer_iter->get()};
     wetbuffer->mInUse = true;
 
     auto acnmap_end = AmbiIndex::FromACN.begin() + count;
@@ -1061,7 +1084,7 @@ void aluInitEffectPanning(ALeffectslot *slot, ALCcontext *context)
         [](const uint8_t &acn) noexcept -> BFChannelConfig
         { return BFChannelConfig{1.0f, acn}; });
     std::fill(iter, slot->Wet.AmbiMap.end(), BFChannelConfig{});
-    slot->Wet.Buffer = {wetbuffer->mBuffer.data(), count};
+    slot->Wet.Buffer = wetbuffer->mBuffer;
 }
 
 
-- 
2.11.4.GIT