From cede51ae0ce834b3442a78c91e196f9bef343666 Mon Sep 17 00:00:00 2001
From: locphamtran <tranloclqd@gmail.com>
Date: Fri, 4 Sep 2026 17:34:54 +0700
Subject: [PATCH] M5.4: VST3 host conformance (Reaper-style) for FX GUI attach

- queryInterface now answers FUnknown::iid + own iid (IComponentHandler /
  IPlugFrame) with addRef+this per SDK QUERY_INTERFACE contract; plugins that
  QI the host handler no longer get kNoInterface unconditionally.
- setBusArrangements negotiation before activateBus: offer mono/stereo for
  <=2ch audio buses, keep wider arrangements; result logged, not fatal.
  Matches REAPER load path so Ozone-class editors see a valid arrangement
  on first attach. Local float regression: Ozone 11 editor opens OK.
---
 native_bridge/src/RenderFxJob.cpp | 56 +++++++++++++++++++++++++++++--
 1 file changed, 53 insertions(+), 3 deletions(-)

diff --git a/native_bridge/src/RenderFxJob.cpp b/native_bridge/src/RenderFxJob.cpp
index b9cf880..6f6e29c 100644
--- a/native_bridge/src/RenderFxJob.cpp
+++ b/native_bridge/src/RenderFxJob.cpp
@@ -25,6 +25,7 @@
 #include "public.sdk/source/vst/vstpresetfile.h"
 #include "public.sdk/source/common/memorystream.h"
 #include "pluginterfaces/vst/ivstaudioprocessor.h"
+#include "pluginterfaces/vst/vstspeaker.h"
 #include "pluginterfaces/vst/ivstcomponent.h"
 #include "pluginterfaces/vst/ivsteditcontroller.h"
 #include "pluginterfaces/vst/ivstprocesscontext.h"
@@ -355,7 +356,18 @@ using Steinberg::Vst::kSample32;
 
 class HostComponentHandlerFx : public IComponentHandler {
 public:
-    tresult queryInterface(const char*, void** v) override { *v = nullptr; return kNoInterface; }
+    tresult queryInterface(const char* iid, void** v) override {
+        // FUnknown contract: answer for our own iid (+FUnknown::iid) with
+        // addRef + this; kNoInterface otherwise (SDK QUERY_INTERFACE pattern).
+        if (Steinberg::FUnknownPrivate::iidEqual(iid, Steinberg::FUnknown::iid) ||
+            Steinberg::FUnknownPrivate::iidEqual(iid, IComponentHandler::iid)) {
+            addRef();
+            *v = this;
+            return kResultOk;
+        }
+        *v = nullptr;
+        return kNoInterface;
+    }
     Steinberg::uint32 addRef() override { return 1; }
     Steinberg::uint32 release() override { return 1; }
     tresult beginEdit(Steinberg::Vst::ParamID) override { return kResultOk; }
@@ -377,7 +389,15 @@ using Steinberg::kPlatformTypeHWND;
 // Minimal IPlugFrame so the plugin can resize its editor view.
 class HostPlugFrameFx : public Steinberg::IPlugFrame {
 public:
-    tresult queryInterface(const char*, void** v) override {
+    tresult queryInterface(const char* iid, void** v) override {
+        // FUnknown contract: answer for our own iid (+FUnknown::iid) with
+        // addRef + this; kNoInterface otherwise (SDK QUERY_INTERFACE pattern).
+        if (Steinberg::FUnknownPrivate::iidEqual(iid, Steinberg::FUnknown::iid) ||
+            Steinberg::FUnknownPrivate::iidEqual(iid, Steinberg::IPlugFrame::iid)) {
+            addRef();
+            *v = this;
+            return kResultOk;
+        }
         *v = nullptr;
         return kNoInterface;
     }
@@ -515,8 +535,38 @@ bool vst3FxLoadInner(Vst3FxState* s, const std::string& path, double sampleRate,
     std::cerr << "[RenderFx] STEP connection points OK" << std::endl;
 
     int32 numAudioInputs = component->getBusCount(kAudio, kInput);
-    for (int32 i = 0; i < numAudioInputs; ++i) component->activateBus(kAudio, kInput, i, true);
     int32 numAudioOutputs = component->getBusCount(kAudio, kOutput);
+    // Reaper-style negotiation BEFORE activation: offer mono/stereo for the
+    // <=2ch audio busses so plugins (Ozone 11 family) never see an empty or
+    // unset arrangement on their first GUI attach. Wider busses keep their
+    // current arrangement. Failure to negotiate is not fatal (log only).
+    {
+        FUnknownPtr<IAudioProcessor> proc(component);
+        if (proc) {
+            std::vector<Steinberg::Vst::SpeakerArrangement> inArr, outArr;
+            for (int32 i = 0; i < numAudioInputs; ++i) {
+                Steinberg::Vst::SpeakerArrangement arr = 0;
+                proc->getBusArrangement(kInput, i, arr);
+                int32 ch = Steinberg::Vst::SpeakerArr::getChannelCount(arr);
+                inArr.push_back(ch == 1 ? Steinberg::Vst::SpeakerArr::kMono
+                                        : (ch == 2 ? Steinberg::Vst::SpeakerArr::kStereo : arr));
+            }
+            for (int32 i = 0; i < numAudioOutputs; ++i) {
+                Steinberg::Vst::SpeakerArrangement arr = 0;
+                proc->getBusArrangement(kOutput, i, arr);
+                int32 ch = Steinberg::Vst::SpeakerArr::getChannelCount(arr);
+                outArr.push_back(ch == 1 ? Steinberg::Vst::SpeakerArr::kMono
+                                         : (ch == 2 ? Steinberg::Vst::SpeakerArr::kStereo : arr));
+            }
+            tresult res = proc->setBusArrangements(inArr.data(), (int32)inArr.size(),
+                                                   outArr.data(), (int32)outArr.size());
+            std::cerr << "[RenderFx] STEP bus arrangements "
+                      << (res == kResultOk || res == kResultTrue ? "OK" : "skip")
+                      << " (ain=" << numAudioInputs << " aout=" << numAudioOutputs << ")"
+                      << std::endl;
+        }
+    }
+    for (int32 i = 0; i < numAudioInputs; ++i) component->activateBus(kAudio, kInput, i, true);
     for (int32 i = 0; i < numAudioOutputs; ++i) component->activateBus(kAudio, kOutput, i, true);
     int32 numEventInputs = component->getBusCount(kEvent, kInput);
     for (int32 i = 0; i < numEventInputs; ++i) component->activateBus(kEvent, kInput, i, true);