Add support for double precision audio #34

So far I've only seen REAPER running iZotope Rx plugins utilize this.

CHANGELOG.md

@@ -6,6 +6,14 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic
 Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Added
+
+- Added support for double precision audio processing. This is not very widely
+  used, but some plugins running under REAPER can make use of this. Without this
+  those plugins would cause REAPER's audio engine to segfault.
+
 ## [1.5.0] - 2020-08-21
 
 ### Added

README.md

@@ -466,7 +466,9 @@ There are also some VST2.X extension features that have not been implemented yet
 because I haven't needed them myself. Let me know if you need any of these
 features for a certain plugin or VST host:
 
-- Double precision audio (`processDoubleReplacing`).
+- Double precision audio (`processDoubleReplacing`). **This is now implemented
+  on the master branch and will be part of the next release. Without this some
+  specific plugins will crash under REAPER.**
 - SysEx messages. In addition to MIDI, VST 2.4 also supports SysEx. I don't know
   of any hosts or plugins that use this, but please let me know if this is
   needed for something.

docs/architecture.md

@@ -79,12 +79,15 @@ as the _Windows VST plugin_. The whole process works as follows:
      plugin through the Wine VST host using a single socket because they're very
      similar and don't need any complicated behaviour.
 
-   - Calls from the native VST host to the plugin's `processReplacing()`
-     function. This function gets forwarded to the Windows VST plugin through
-     the Wine VST. In the rare event that the plugin does not support
-     `processReplacing()` and only supports The deprecated commutative
-     `process()` function, then the Wine VST host will emulate the behavior of
-     `processReplacing()` instead.
+   - Calls from the native VST host to the plugin's `processReplacing()` and
+     `processDoubleReplacing()` functions. These functions get forwarded to the
+     Windows VST plugin through the Wine VST host. In the rare event that the
+     plugin does not support `processReplacing()` and only supports The
+     deprecated commutative `process()` function, then the Wine VST host will
+     emulate the behavior of `processReplacing()` instead. Single and double
+     precision audio go over the same socket since the host will only call one
+     or the other, and we just use a variant to determine which one should be
+     called on the Wine host side.
 
    - And finally there's a separate socket for control messages. At the moment
      this is only used to transfer the Windows VST plugin's `AEffect` object to

src/common/serialization.h

@@ -551,12 +551,18 @@ struct ParameterResult {
 /**
  * A buffer of audio for the plugin to process, or the response of that
  * processing. The number of samples is encoded in each audio buffer's length.
+ * This is used for both `process()/processReplacing()` and
+ * `processDoubleReplacing()`.
  */
 struct AudioBuffers {
     /**
-     * An audio buffer for each of the plugin's audio channels.
+     * An audio buffer for each of the plugin's audio channels. This uses floats
+     * or doubles depending on whether `process()/processReplacing()` or
+     * `processDoubleReplacing()` got called.
      */
-    std::vector<std::vector<float>> buffers;
+    std::variant<std::vector<std::vector<float>>,
+                 std::vector<std::vector<double>>>
+        buffers;
 
     /**
      * The number of frames in a sample. If buffers is not empty, then
@@ -566,8 +572,20 @@ struct AudioBuffers {
 
     template <typename S>
     void serialize(S& s) {
-        s.container(buffers, max_audio_channels,
-                    [](S& s, auto& v) { s.container4b(v, max_buffer_size); });
+        s.ext(
+            buffers,
+            bitsery::ext::StdVariant{
+                [](S& s, std::vector<std::vector<float>>& buffer) {
+                    s.container(buffer, max_audio_channels, [](S& s, auto& v) {
+                        s.container4b(v, max_buffer_size);
+                    });
+                },
+                [](S& s, std::vector<std::vector<double>>& buffer) {
+                    s.container(buffer, max_audio_channels, [](S& s, auto& v) {
+                        s.container8b(v, max_buffer_size);
+                    });
+                },
+            });
         s.value4b(sample_frames);
     }
 };

src/include/vestige/aeffectx.h

@@ -298,6 +298,15 @@ class AEffect {
     int version;
     // processReplacing 50-53
     void(VST_CALL_CONV* processReplacing)(AEffect*, float**, float**, int);
+    // Found at
+    // https://git.iem.at/zmoelnig/VeSTige/-/blob/b0e67183e155fec32dd85a2c7b5c2e4b58407323/vestige.h#L323
+    // The offset was also found based on a segfualt in REAPER's audio audio
+    // engine when it tried to call this function for the Rx7 plugins when
+    // yabridge did not yet implement it
+    void(VST_CALL_CONV* processDoubleReplacing)(AEffect*,
+                                                double**,
+                                                double**,
+                                                int);
 };
 
 class VstTimeInfo {

src/plugin/plugin-bridge.cpp

@@ -33,8 +33,9 @@ namespace fs = boost::filesystem;
 intptr_t dispatch_proxy(AEffect*, int, int, intptr_t, void*, float);
 void process_proxy(AEffect*, float**, float**, int);
 void process_replacing_proxy(AEffect*, float**, float**, int);
-void setParameter_proxy(AEffect*, int, float);
-float getParameter_proxy(AEffect*, int);
+void process_double_replacing_proxy(AEffect*, double**, double**, int);
+void set_parameter_proxy(AEffect*, int, float);
+float get_parameter_proxy(AEffect*, int);
 
 /**
  * Fetch the bridge instance stored in an unused pointer from a VST plugin. This
@@ -130,9 +131,10 @@ PluginBridge::PluginBridge(audioMasterCallback host_callback)
     plugin.ptr3 = this;
     plugin.dispatcher = dispatch_proxy;
     plugin.process = process_proxy;
-    plugin.setParameter = setParameter_proxy;
-    plugin.getParameter = getParameter_proxy;
+    plugin.setParameter = set_parameter_proxy;
+    plugin.getParameter = get_parameter_proxy;
     plugin.processReplacing = process_replacing_proxy;
+    plugin.processDoubleReplacing = process_double_replacing_proxy;
 
     // For our communication we use simple threads and blocking operations
     // instead of asynchronous IO since communication has to be handled in
@@ -512,14 +514,12 @@ intptr_t PluginBridge::dispatch(AEffect* /*plugin*/,
                       value, data, option);
 }
 
-void PluginBridge::process_replacing(AEffect* /*plugin*/,
-                                     float** inputs,
-                                     float** outputs,
-                                     int sample_frames) {
+template <typename T>
+void PluginBridge::do_process(T** inputs, T** outputs, int sample_frames) {
     // The inputs and outputs arrays should be `[num_inputs][sample_frames]` and
     // `[num_outputs][sample_frames]` floats large respectfully.
-    std::vector<std::vector<float>> input_buffers(
-        plugin.numInputs, std::vector<float>(sample_frames));
+    std::vector<std::vector<T>> input_buffers(plugin.numInputs,
+                                              std::vector<T>(sample_frames));
     for (int channel = 0; channel < plugin.numInputs; channel++) {
         std::copy(inputs[channel], inputs[channel] + sample_frames,
                   input_buffers[channel].begin());
@@ -531,11 +531,13 @@ void PluginBridge::process_replacing(AEffect* /*plugin*/,
     // Write the results back to the `outputs` arrays
     const auto response =
         read_object<AudioBuffers>(host_vst_process_replacing, process_buffer);
+    const auto& response_buffers =
+        std::get<std::vector<std::vector<T>>>(response.buffers);
 
-    assert(response.buffers.size() == static_cast<size_t>(plugin.numOutputs));
+    assert(response_buffers.size() == static_cast<size_t>(plugin.numOutputs));
     for (int channel = 0; channel < plugin.numOutputs; channel++) {
-        std::copy(response.buffers[channel].begin(),
-                  response.buffers[channel].end(), outputs[channel]);
+        std::copy(response_buffers[channel].begin(),
+                  response_buffers[channel].end(), outputs[channel]);
     }
 
     // Plugins are allowed to send MIDI events during processing using a host
@@ -553,6 +555,20 @@ void PluginBridge::process_replacing(AEffect* /*plugin*/,
     incoming_midi_events.clear();
 }
 
+void PluginBridge::process_replacing(AEffect* /*plugin*/,
+                                     float** inputs,
+                                     float** outputs,
+                                     int sample_frames) {
+    do_process<float>(inputs, outputs, sample_frames);
+}
+
+void PluginBridge::process_double_replacing(AEffect* /*plugin*/,
+                                            double** inputs,
+                                            double** outputs,
+                                            int sample_frames) {
+    do_process<double>(inputs, outputs, sample_frames);
+}
+
 float PluginBridge::get_parameter(AEffect* /*plugin*/, int index) {
     logger.log_get_parameter(index);
 
@@ -691,6 +707,10 @@ void process_proxy(AEffect* plugin,
                    float** inputs,
                    float** outputs,
                    int sample_frames) {
+    // FIXME: This is incorrect, and I only noticed just now. I'm 99% sure no
+    //        hosts actually use this, but this will overwrite the buffer. On
+    //        the plugin side we do properly handle plugins that only support
+    //        the old cumulative process function.
     return get_bridge_instance(*plugin).process_replacing(
         plugin, inputs, outputs, sample_frames);
 }
@@ -703,10 +723,18 @@ void process_replacing_proxy(AEffect* plugin,
         plugin, inputs, outputs, sample_frames);
 }
 
-void setParameter_proxy(AEffect* plugin, int index, float value) {
+void process_double_replacing_proxy(AEffect* plugin,
+                                    double** inputs,
+                                    double** outputs,
+                                    int sample_frames) {
+    return get_bridge_instance(*plugin).process_double_replacing(
+        plugin, inputs, outputs, sample_frames);
+}
+
+void set_parameter_proxy(AEffect* plugin, int index, float value) {
     return get_bridge_instance(*plugin).set_parameter(plugin, index, value);
 }
 
-float getParameter_proxy(AEffect* plugin, int index) {
+float get_parameter_proxy(AEffect* plugin, int index) {
     return get_bridge_instance(*plugin).get_parameter(plugin, index);
 }

src/plugin/plugin-bridge.h

@@ -69,9 +69,33 @@ class PluginBridge {
                            float** inputs,
                            float** outputs,
                            int sample_frames);
+    /**
+     * The same as `PluginBridge::process_replacing`, but for double precision
+     * audio. Support for this on both the plugin and host side is pretty rare,
+     * but REAPER supports it. This reuses the same infrastructure as
+     * `process_replacing` is using since the host will only call one or the
+     * other.
+     */
+    void process_double_replacing(AEffect* plugin,
+                                  double** inputs,
+                                  double** outputs,
+                                  int sample_frames);
     float get_parameter(AEffect* plugin, int index);
     void set_parameter(AEffect* plugin, int index, float value);
 
+    /**
+     * Process audio and handle plugin-generated MIDI events afterwards.
+     *
+     * @tparam T The sample type. Should be either `float` for single preceision
+     *   audio processing called through `processReplacing`, or `double` for
+     *   double precision audio through `processDoubleReplacing`.
+     *
+     * @see PluginBridge::process_replacing
+     * @see PluginBridge::process_double_replacing
+     */
+    template <typename T>
+    void do_process(T** inputs, T** outputs, int sample_frames);
+
     /**
      * The configuration for this instance of yabridge. Set based on the values
      * from a `yabridge.toml`, if it exists.
@@ -198,8 +222,8 @@ class PluginBridge {
     std::jthread wine_io_handler;
 
     /**
-     * A scratch buffer for sending and receiving data during `process` and
-     * `processReplacing` calls.
+     * A scratch buffer for sending and receiving data during `process`,
+     * `processReplacing` and `processDoubleReplacing` calls.
      */
     std::vector<uint8_t> process_buffer;
 

src/wine-host/bridges/vst2.cpp

@@ -278,60 +278,107 @@ void Vst2Bridge::handle_parameters() {
 }
 
 void Vst2Bridge::handle_process_replacing() {
-    std::vector<std::vector<float>> output_buffers(plugin->numOutputs);
+    // These are used as scratch buffers to prevent unnecessary allocations.
+    // Since don't know in advance whether the host will call `processReplacing`
+    // or `processDoubleReplacing` we'll just create both.
+    std::vector<std::vector<float>> output_buffers_single_precision(
+        plugin->numOutputs);
+    std::vector<std::vector<double>> output_buffers_double_precision(
+        plugin->numOutputs);
 
     while (true) {
         try {
             auto request = read_object<AudioBuffers>(host_vst_process_replacing,
                                                      process_buffer);
-
-            // The process functions expect a `float**` for their inputs and
-            // their outputs
-            std::vector<float*> inputs;
-            for (auto& buffer : request.buffers) {
-                inputs.push_back(buffer.data());
-            }
-
-            // We reuse the buffers to avoid some unnecessary heap allocations,
-            // so we need to make sure the buffers are large enough since
-            // plugins can change their output configuration
-            std::vector<float*> outputs;
-            output_buffers.resize(plugin->numOutputs);
-            for (auto& buffer : output_buffers) {
-                buffer.resize(request.sample_frames);
-                outputs.push_back(buffer.data());
-            }
-
             // Let the plugin process the MIDI events that were received since
             // the last buffer, and then clean up those events. This approach
             // should not be needed but Kontakt only stores pointers to rather
             // than copies of the events.
-            {
-                std::lock_guard lock(next_buffer_midi_events_mutex);
+            std::lock_guard lock(next_buffer_midi_events_mutex);
 
-                // Any plugin made in the last fifteen years or so should
-                // support `processReplacing`. In the off chance it does not we
-                // can just emulate this behavior ourselves.
-                if (plugin->processReplacing) {
-                    plugin->processReplacing(plugin, inputs.data(),
-                                             outputs.data(),
-                                             request.sample_frames);
-                } else {
-                    // If we zero out this buffer then the behavior is the same
-                    // as `processReplacing``
-                    for (std::vector<float>& buffer : output_buffers) {
-                        std::fill(buffer.begin(), buffer.end(), 0.0);
-                    }
+            // Since the host should only be calling one of `process()`,
+            // processReplacing()` or `processDoubleReplacing()`, we can all
+            // handle them over the same socket. We pick which one to call
+            // depending on the type of data we got sent and the plugin's
+            // reported support for these functions.
+            std::visit(
+                overload{
+                    [&](std::vector<std::vector<float>>& input_buffers) {
+                        // The process functions expect a `float**` for their
+                        // inputs and their outputs
+                        std::vector<float*> inputs;
+                        for (auto& buffer : input_buffers) {
+                            inputs.push_back(buffer.data());
+                        }
 
-                    plugin->process(plugin, inputs.data(), outputs.data(),
-                                    request.sample_frames);
-                }
+                        // We reuse the buffers to avoid some unnecessary heap
+                        // allocations, so we need to make sure the buffers are
+                        // large enough since plugins can change their output
+                        // configuration. The type we're using here (single
+                        // precision floats vs double precisioon doubles) should
+                        // be the same as the one we're sending in our response.
+                        std::vector<float*> outputs;
+                        output_buffers_single_precision.resize(
+                            plugin->numOutputs);
+                        for (auto& buffer : output_buffers_single_precision) {
+                            buffer.resize(request.sample_frames);
+                            outputs.push_back(buffer.data());
+                        }
 
-                next_audio_buffer_midi_events.clear();
-            }
+                        // Any plugin made in the last fifteen years or so
+                        // should support `processReplacing`. In the off chance
+                        // it does not we can just emulate this behavior
+                        // ourselves.
+                        if (plugin->processReplacing) {
+                            plugin->processReplacing(plugin, inputs.data(),
+                                                     outputs.data(),
+                                                     request.sample_frames);
+                        } else {
+                            // If we zero out this buffer then the behavior is
+                            // the same as `processReplacing``
+                            for (std::vector<float>& buffer :
+                                 output_buffers_single_precision) {
+                                std::fill(buffer.begin(), buffer.end(), 0.0);
+                            }
 
-            AudioBuffers response{output_buffers, request.sample_frames};
-            write_object(host_vst_process_replacing, response, process_buffer);
+                            plugin->process(plugin, inputs.data(),
+                                            outputs.data(),
+                                            request.sample_frames);
+                        }
+
+                        AudioBuffers response{output_buffers_single_precision,
+                                              request.sample_frames};
+                        write_object(host_vst_process_replacing, response,
+                                     process_buffer);
+                    },
+                    [&](std::vector<std::vector<double>>& input_buffers) {
+                        // Exactly the same as the above, but for double
+                        // precision audio
+                        std::vector<double*> inputs;
+                        for (auto& buffer : input_buffers) {
+                            inputs.push_back(buffer.data());
+                        }
+
+                        std::vector<double*> outputs;
+                        output_buffers_double_precision.resize(
+                            plugin->numOutputs);
+                        for (auto& buffer : output_buffers_double_precision) {
+                            buffer.resize(request.sample_frames);
+                            outputs.push_back(buffer.data());
+                        }
+
+                        plugin->processDoubleReplacing(plugin, inputs.data(),
+                                                       outputs.data(),
+                                                       request.sample_frames);
+
+                        AudioBuffers response{output_buffers_double_precision,
+                                              request.sample_frames};
+                        write_object(host_vst_process_replacing, response,
+                                     process_buffer);
+                    }},
+                request.buffers);
+
+            next_audio_buffer_midi_events.clear();
         } catch (const boost::system::system_error&) {
             // The plugin has cut off communications, so we can shut down this
             // host application

src/wine-host/bridges/vst2.h

@@ -242,7 +242,8 @@ class Vst2Bridge {
      */
     Win32Thread parameters_handler;
     /**
-     * The thread that handles calls to `processReplacing` (and `process`).
+     * The thread that handles calls to `processReplacing` (and `process` as a
+     * fallback) and `processDoubleReplacing`.
      */
     Win32Thread process_replacing_handler;