From b6f96fc9201016caecbbf68a1308f05cd8ea4677 Mon Sep 17 00:00:00 2001
From: Robbert van der Helm <mail@robbertvanderhelm.nl>
Date: Thu, 6 May 2021 18:32:46 +0200
Subject: [PATCH] Cache IAudioProcessor::canProcessSampleSize()

---
 CHANGELOG.md                                  |  5 +++
 .../bridges/vst3-impls/plugin-proxy.cpp       | 35 ++++++++++++++++---
 src/plugin/bridges/vst3-impls/plugin-proxy.h  |  5 +++
 3 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1615f818..c1ac4363 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,11 @@ Versioning](https://semver.org/spec/v2.0.0.html).
 - Added a timed cache for the `IPluginView::canResize()` VST3 function, so value
   will be remembered during an active resize. This makes resizing VST3 plugin
   editor windows more responsive.
+- Add a cache for VST3 function calls where the host asks the plugin whether it
+  can process 32-bit or 64-bit floating point audio. Some hosts will call this
+  function every processing cycle even though the value doesn't change. Caching
+  this can significantly reduce the overhead of bridging VST3 plugins under
+  those hosts.
 
 ## [3.2.0] - 2021-05-03
 
diff --git a/src/plugin/bridges/vst3-impls/plugin-proxy.cpp b/src/plugin/bridges/vst3-impls/plugin-proxy.cpp
index 3438299b..14e81fa8 100644
--- a/src/plugin/bridges/vst3-impls/plugin-proxy.cpp
+++ b/src/plugin/bridges/vst3-impls/plugin-proxy.cpp
@@ -139,10 +139,37 @@ tresult PLUGIN_API Vst3PluginProxyImpl::getBusArrangement(
 
 tresult PLUGIN_API
 Vst3PluginProxyImpl::canProcessSampleSize(int32 symbolicSampleSize) {
-    return bridge.send_audio_processor_message(
-        YaAudioProcessor::CanProcessSampleSize{
-            .instance_id = instance_id(),
-            .symbolic_sample_size = symbolicSampleSize});
+    const auto request = YaAudioProcessor::CanProcessSampleSize{
+        .instance_id = instance_id(),
+        .symbolic_sample_size = symbolicSampleSize};
+
+    {
+        std::lock_guard lock(function_result_cache_mutex);
+        if (auto it = function_result_cache.can_process_sample_size.find(
+                symbolicSampleSize);
+            it != function_result_cache.can_process_sample_size.end()) {
+            const bool log_response = bridge.logger.log_request(true, request);
+            if (log_response) {
+                bridge.logger.log_response(
+                    true,
+                    YaAudioProcessor::CanProcessSampleSize::Response(
+                        it->second),
+                    true);
+            }
+
+            return *function_result_cache.parameter_count;
+        }
+    }
+
+    const tresult result = bridge.send_audio_processor_message(request);
+
+    {
+        std::lock_guard lock(function_result_cache_mutex);
+        function_result_cache.can_process_sample_size[symbolicSampleSize] =
+            result;
+    }
+
+    return result;
 }
 
 uint32 PLUGIN_API Vst3PluginProxyImpl::getLatencySamples() {
diff --git a/src/plugin/bridges/vst3-impls/plugin-proxy.h b/src/plugin/bridges/vst3-impls/plugin-proxy.h
index df9dbc8a..41a69e6f 100644
--- a/src/plugin/bridges/vst3-impls/plugin-proxy.h
+++ b/src/plugin/bridges/vst3-impls/plugin-proxy.h
@@ -531,6 +531,11 @@ class Vst3PluginProxyImpl : public Vst3PluginProxy {
      * @see function_result_cache
      */
     struct FunctionResultCache {
+        /**
+         * Memoizes `IAudioProcessor::canProcessSampleSize()`, since some hosts
+         * call this every processing cycle.
+         */
+        std::map<int32, tresult> can_process_sample_size;
         /**
          * Memoizes `IEditController::getParameterCount()`.
          */