Introduce an Event system to VideoCommon

A lot of the remaining complexity in Renderer is the massive Swap function
which tries to handle a bunch of FrameBegin/FrameEnd events.

Rather than create a new place for it. This event system will try
to distribute it all over the place

6 files changed, 186 insertions, 0 deletions

diff --git a/Source/Core/Common/CMakeLists.txt b/Source/Core/Common/CMakeLists.txt
index 6e49f7b7a6..bab78766da 100644
--- a/Source/Core/Common/CMakeLists.txt
+++ b/Source/Core/Common/CMakeLists.txt
@@ -46,6 +46,7 @@ add_library(common
   EnumFormatter.h
   EnumMap.h
   Event.h
+  EventHook.h
   FatFsUtil.cpp
   FatFsUtil.h
   FileSearch.cpp
@@ -115,6 +116,7 @@ add_library(common
   SocketContext.cpp
   SocketContext.h
   SPSCQueue.h
+  StringLiteral.h
   StringUtil.cpp
   StringUtil.h
   SymbolDB.cpp
diff --git a/Source/Core/Common/EventHook.h b/Source/Core/Common/EventHook.h
new file mode 100644
index 0000000000..265013827a
--- /dev/null
+++ b/Source/Core/Common/EventHook.h
@@ -0,0 +1,79 @@
+// Copyright 2023 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include "Common/Logging/Log.h"
+#include "Common/StringLiteral.h"
+
+#include <functional>
+#include <memory>
+#include <string>
+#include <string_view>
+#include <vector>
+
+// A hookable event system.
+
+// Define Events in a header as:
+//
+//     using MyLoveyEvent = Event<"My lovely event", std::string>;
+//
+// Register listeners anywhere you need them as:
+//    EventHook myHook = MyLoveyEvent::Register([](std::string foo) {
+//       // Do something
+//   }, "Name of the hook");
+//
+// The hook will be automatically unregistered when the EventHook object goes out of scope.
+// Trigger events by doing:
+//
+//   MyLoveyEvent::Trigger("Hello world");
+//
+
+struct HookBase
+{
+  virtual ~HookBase() = default;
+};
+
+using EventHook = std::unique_ptr<HookBase>;
+
+template<StringLiteral EventName, typename... CallbackArgs>
+class Event
+{
+public:
+  using CallbackType = std::function<void(CallbackArgs...)>;
+
+private:
+  struct HookImpl : public HookBase
+  {
+    ~HookImpl() override { Event::Remove(this); }
+    HookImpl(CallbackType callback, std::string name) : m_fn(callback), m_name(name){ }
+    CallbackType m_fn;
+    std::string m_name;
+  };
+public:
+
+  // Returns a handle that will unregister the listener when destroyed.
+  static EventHook Register(CallbackType callback, std::string name)
+  {
+    DEBUG_LOG_FMT(COMMON, "Registering {} handler at {} event hook", name, EventName.value);
+    auto handle = std::make_unique<HookImpl>(callback, name);
+    m_listeners.push_back(handle.get());
+    return handle;
+  }
+
+  static void Trigger(CallbackArgs... args)
+  {
+    for (auto& handle : m_listeners)
+      handle->m_fn(args...);
+  }
+
+private:
+  static void Remove(HookImpl* handle)
+  {
+    auto it = std::find(m_listeners.begin(), m_listeners.end(), handle);
+    if (it != m_listeners.end())
+      m_listeners.erase(it);
+  }
+
+  inline static std::vector<HookImpl*> m_listeners = {};
+};
diff --git a/Source/Core/Common/StringLiteral.h b/Source/Core/Common/StringLiteral.h
new file mode 100644
index 0000000000..6227d48ed6
--- /dev/null
+++ b/Source/Core/Common/StringLiteral.h
@@ -0,0 +1,17 @@
+// Copyright 2023 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <algorithm>
+
+// A useful template for passing string literals as arguments to templates
+// from: https://ctrpeach.io/posts/cpp20-string-literal-template-parameters/
+template<size_t N>
+struct StringLiteral {
+  consteval StringLiteral(const char (&str)[N]) {
+      std::copy_n(str, N, value);
+  }
+
+  char value[N];
+};
diff --git a/Source/Core/DolphinLib.props b/Source/Core/DolphinLib.props
index 9bf63bbb51..470d303e21 100644
--- a/Source/Core/DolphinLib.props
+++ b/Source/Core/DolphinLib.props
@@ -46,6 +46,7 @@
     <ClInclude Include="Common\EnumFormatter.h" />
     <ClInclude Include="Common\EnumMap.h" />
     <ClInclude Include="Common\Event.h" />
+    <ClInclude Include="Common\EventHook.h" />
     <ClInclude Include="Common\FatFsUtil.h" />
     <ClInclude Include="Common\FileSearch.h" />
     <ClInclude Include="Common\FileUtil.h" />
@@ -145,6 +146,7 @@
     <ClInclude Include="Common\SFMLHelper.h" />
     <ClInclude Include="Common\SocketContext.h" />
     <ClInclude Include="Common\SPSCQueue.h" />
+    <ClInclude Include="Common\StringLiteral.h" />
     <ClInclude Include="Common\StringUtil.h" />
     <ClInclude Include="Common\Swap.h" />
     <ClInclude Include="Common\SymbolDB.h" />
@@ -713,6 +715,7 @@
     <ClInclude Include="VideoCommon\VideoBackendBase.h" />
     <ClInclude Include="VideoCommon\VideoCommon.h" />
     <ClInclude Include="VideoCommon\VideoConfig.h" />
+    <ClInclude Include="VideoCommon\VideoEvents.h" />
     <ClInclude Include="VideoCommon\VideoState.h" />
     <ClInclude Include="VideoCommon\XFMemory.h" />
     <ClInclude Include="VideoCommon\XFStructs.h" />
diff --git a/Source/Core/VideoCommon/CMakeLists.txt b/Source/Core/VideoCommon/CMakeLists.txt
index 4507904afd..5428facc55 100644
--- a/Source/Core/VideoCommon/CMakeLists.txt
+++ b/Source/Core/VideoCommon/CMakeLists.txt
@@ -163,6 +163,7 @@ add_library(videocommon
   VertexShaderManager.h
   VideoBackendBase.cpp
   VideoBackendBase.h
+  VideoEvents.h
   VideoCommon.h
   VideoConfig.cpp
   VideoConfig.h
diff --git a/Source/Core/VideoCommon/VideoEvents.h b/Source/Core/VideoCommon/VideoEvents.h
new file mode 100644
index 0000000000..bb95296ebd
--- /dev/null
+++ b/Source/Core/VideoCommon/VideoEvents.h
@@ -0,0 +1,84 @@
+// Copyright 2023 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include "Common/CommonTypes.h"
+#include "Common/EventHook.h"
+
+
+// Called when certain video config setting are changed
+using ConfigChangedEvent = Event<"ConfigChanged", u32>;
+
+// An event called just before the first draw call of a frame
+using BeforeFrameEvent = Event<"BeforeFrame">;
+
+// An event called after the frame XFB copy begins processing on the host GPU.
+// Useful for "once per frame" usecases.
+// Note: In a few rare cases, games do multiple XFB copies per frame and join them while presenting.
+//       If this matters to your usecase, you should use BeforePresent instead.
+using AfterFrameEvent = Event<"AfterFrame">;
+
+struct PresentInfo
+{
+    enum class PresentReason
+    {
+      Immediate, // FIFO is Presenting the XFB immediately, straight after the XFB copy
+      VideoInterface, // VideoInterface has triggered a present with a new frame
+      VideoInterfaceDuplicate, // VideoInterface has triggered a present with a duplicate frame
+    };
+
+    // The number of (unique) frames since the emulated console booted
+    u64 frame_count;
+
+
+    // The number of presents since the video backend was initialized.
+    // never goes backwards.
+    u64 present_count;
+
+    // The frame is identical to the previous frame
+    PresentReason reason;
+
+    // The exact emulated time of the when real hardware would have presented this frame
+    // FIXME: Immediate should predict the timestamp of this present
+     u64 emulated_timestamp;
+
+    // TODO:
+    // u64 intended_present_time;
+
+    // AfterPresent only: The actual time the frame was presented
+    u64 actual_present_time = 0;
+
+    enum class PresentTimeAccuracy
+    {
+        // The Driver/OS has given us an exact timestamp of when the first line of the frame started
+        // scanning out to the monitor
+        PresentOnScreenExact,
+
+        // An approximate timestamp of scanout.
+        PresentOnScreen,
+
+        // Dolphin doesn't have visibility of the present time. But the present operation has
+        // been queued with the GPU driver and will happen in the near future.
+        PresentInProgress,
+
+        // Not implemented
+        Unimplemented,
+    };
+
+    // Accuracy of actual_present_time
+    PresentTimeAccuracy present_time_accuracy = PresentTimeAccuracy::Unimplemented;
+};
+
+// An event called just as a frame is queued for presentation.
+// The exact timing of this event depends on the "Immediately Present XFB" option.
+//
+// If enabled, this event will trigger immediately after AfterFrame
+// If disabled, this event won't trigger until the emulated interface starts drawing out a new frame.
+//
+// frame_count: The number of frames
+using BeforePresentEvent = Event<"BeforePresent", PresentInfo&>;
+
+// An event that is triggered after a frame is presented.
+// The exact timing of this event depends on backend/driver support.
+using AfterPresentEvent = Event<"AfterPresent", PresentInfo&>;