VideoCommon: Add "Smooth Early Presentation" setting to improve frame pacing with ImmediateXFB and/or RushFramePresentation.

Source/Core/VideoCommon/Present.cpp

@@ -163,9 +163,12 @@ void Presenter::ViSwap(u32 xfb_addr, u32 fb_width, u32 fb_stride, u32 fb_height,
 {
   bool is_duplicate = FetchXFB(xfb_addr, fb_width, fb_stride, fb_height, ticks);
 
-  PresentInfo present_info;
-  present_info.emulated_timestamp = ticks;
-  present_info.present_count = m_present_count++;
+  PresentInfo present_info{
+      .present_count = m_present_count++,
+      .emulated_timestamp = ticks,
+      .intended_present_time = presentation_time,
+  };
+
   if (is_duplicate)
   {
     present_info.frame_count = m_frame_count - 1;  // Previous frame
@@ -202,13 +205,7 @@ void Presenter::ViSwap(u32 xfb_addr, u32 fb_width, u32 fb_stride, u32 fb_height,
 
   if (!is_duplicate || !g_ActiveConfig.bSkipPresentingDuplicateXFBs)
   {
-    // If RushFramePresentation is enabled, ignore the proper time to present as soon as possible.
-    // The goal is to achieve the lowest possible input latency.
-    if (Config::Get(Config::MAIN_RUSH_FRAME_PRESENTATION))
-      Present();
-    else
-      Present(presentation_time);
-
+    Present(&present_info);
     ProcessFrameDumping(ticks);
 
     video_events.after_present_event.Trigger(present_info);
@@ -221,17 +218,19 @@ void Presenter::ImmediateSwap(u32 xfb_addr, u32 fb_width, u32 fb_stride, u32 fb_
 
   FetchXFB(xfb_addr, fb_width, fb_stride, fb_height, ticks);
 
-  PresentInfo present_info;
-  present_info.emulated_timestamp = ticks;
-  present_info.frame_count = m_frame_count++;
-  present_info.reason = PresentInfo::PresentReason::Immediate;
-  present_info.present_count = m_present_count++;
+  PresentInfo present_info{
+      .frame_count = m_frame_count++,
+      .present_count = m_present_count++,
+      .reason = PresentInfo::PresentReason::Immediate,
+      .emulated_timestamp = ticks,
+      .intended_present_time = m_next_swap_estimated_time,
+  };
 
   auto& video_events = GetVideoEvents();
 
   video_events.before_present_event.Trigger(present_info);
 
-  Present();
+  Present(&present_info);
   ProcessFrameDumping(ticks);
 
   video_events.after_present_event.Trigger(present_info);
@@ -834,7 +833,7 @@ void Presenter::RenderXFBToScreen(const MathUtil::Rectangle<int>& target_rc,
   }
 }
 
-void Presenter::Present(std::optional<TimePoint> presentation_time)
+void Presenter::Present(PresentInfo* present_info)
 {
   m_present_count++;
 
@@ -888,8 +887,16 @@ void Presenter::Present(std::optional<TimePoint> presentation_time)
   {
     std::lock_guard<std::mutex> guard(m_swap_mutex);
 
-    if (presentation_time.has_value())
-      Core::System::GetInstance().GetCoreTiming().SleepUntil(*presentation_time);
+    if (present_info != nullptr)
+    {
+      const auto present_time = GetUpdatedPresentationTime(present_info->intended_present_time);
+
+      Core::System::GetInstance().GetCoreTiming().SleepUntil(present_time);
+
+      // Perhaps in the future a more accurate time can be acquired from the various backends.
+      present_info->actual_present_time = Clock::now();
+      present_info->present_time_accuracy = PresentInfo::PresentTimeAccuracy::PresentInProgress;
+    }
 
     g_gfx->PresentBackbuffer();
   }
@@ -907,6 +914,34 @@ void Presenter::Present(std::optional<TimePoint> presentation_time)
   g_gfx->EndUtilityDrawing();
 }
 
+TimePoint Presenter::GetUpdatedPresentationTime(TimePoint intended_presentation_time)
+{
+  const auto now = Clock::now();
+  const auto arrival_offset = std::min(now - intended_presentation_time, DT{});
+
+  if (!Config::Get(Config::MAIN_SMOOTH_EARLY_PRESENTATION))
+  {
+    m_presentation_time_offset = arrival_offset;
+
+    // When SmoothEarlyPresentation is off and ImmediateXFB or RushFramePresentation are on,
+    //  present as soon as possible as the goal is to achieve low input latency.
+    if (g_ActiveConfig.bImmediateXFB || Config::Get(Config::MAIN_RUSH_FRAME_PRESENTATION))
+      return now;
+
+    return intended_presentation_time;
+  }
+
+  // Adjust slowly backward in time but quickly forward in time.
+  // This keeps the pacing moderately smooth even if games produce regular sporadic bumps.
+  // This was tuned to handle the terrible pacing in Brawl with "Immediate XFB".
+  // Super Mario Galaxy 1 + 2 still perform poorly here in SingleCore mode.
+  const auto adjustment_divisor = (arrival_offset < m_presentation_time_offset) ? 100 : 2;
+
+  m_presentation_time_offset += (arrival_offset - m_presentation_time_offset) / adjustment_divisor;
+
+  return intended_presentation_time + m_presentation_time_offset;
+}
+
 void Presenter::SetKeyMap(const DolphinKeyMap& key_map)
 {
   if (m_onscreen_ui)