System: Add "Skip Duplicate Frame Display" option

Skips the presentation/display of frames that are not unique.
Can be combined with driver-level frame generation to increase
perceptible frame rate. Can result in worse frame pacing, and is
not compatible with syncing to host refresh.

src/duckstation-qt/emulationsettingswidget.cpp

@@ -20,6 +20,8 @@ EmulationSettingsWidget::EmulationSettingsWidget(SettingsWindow* dialog, QWidget
   SettingWidgetBinder::BindWidgetToBoolSetting(sif, m_ui.syncToHostRefreshRate, "Main", "SyncToHostRefreshRate", false);
   SettingWidgetBinder::BindWidgetToBoolSetting(sif, m_ui.optimalFramePacing, "Display", "OptimalFramePacing", false);
   SettingWidgetBinder::BindWidgetToBoolSetting(sif, m_ui.preFrameSleep, "Display", "PreFrameSleep", false);
+  SettingWidgetBinder::BindWidgetToBoolSetting(sif, m_ui.skipPresentingDuplicateFrames, "Display",
+                                               "SkipPresentingDuplicateFrames", false);
   SettingWidgetBinder::BindWidgetToFloatSetting(sif, m_ui.preFrameSleepBuffer, "Display", "PreFrameSleepBuffer",
                                                 Settings::DEFAULT_DISPLAY_PRE_FRAME_SLEEP_BUFFER);
   SettingWidgetBinder::BindWidgetToBoolSetting(sif, m_ui.rewindEnable, "Main", "RewindEnable", false);
@@ -71,7 +73,9 @@ EmulationSettingsWidget::EmulationSettingsWidget(SettingsWindow* dialog, QWidget
   }
   connect(m_ui.turboSpeed, QOverload<int>::of(&QComboBox::currentIndexChanged), this,
           &EmulationSettingsWidget::onTurboSpeedIndexChanged);
-  connect(m_ui.vsync, &QCheckBox::checkStateChanged, this, &EmulationSettingsWidget::onVSyncChanged);
+  connect(m_ui.vsync, &QCheckBox::checkStateChanged, this, &EmulationSettingsWidget::updateSkipDuplicateFramesEnabled);
+  connect(m_ui.syncToHostRefreshRate, &QCheckBox::checkStateChanged, this,
+          &EmulationSettingsWidget::updateSkipDuplicateFramesEnabled);
   connect(m_ui.optimalFramePacing, &QCheckBox::checkStateChanged, this,
           &EmulationSettingsWidget::onOptimalFramePacingChanged);
   connect(m_ui.preFrameSleep, &QCheckBox::checkStateChanged, this, &EmulationSettingsWidget::onPreFrameSleepChanged);
@@ -121,6 +125,11 @@ EmulationSettingsWidget::EmulationSettingsWidget(SettingsWindow* dialog, QWidget
                              tr("Specifies the amount of buffer time added, which reduces the additional sleep time "
                                 "introduced. Higher values increase input latency, but decrease the risk of overrun, "
                                 "or missed frames. Lower values require faster hardware."));
+  dialog->registerWidgetHelp(
+    m_ui.skipPresentingDuplicateFrames, tr("Skip Duplicate Frame Display"), tr("Unchecked"),
+    tr("Skips the presentation/display of frames that are not unique. Can be combined with driver-level frame "
+       "generation to increase perceptible frame rate. Can result in worse frame pacing, and is not compatible with "
+       "syncing to host refresh."));
   dialog->registerWidgetHelp(
     m_ui.rewindEnable, tr("Rewinding"), tr("Unchecked"),
     tr("<b>Enable Rewinding:</b> Saves state periodically so you can rewind any mistakes while playing.<br> "
@@ -133,8 +142,8 @@ EmulationSettingsWidget::EmulationSettingsWidget(SettingsWindow* dialog, QWidget
     tr(
       "Simulates the system ahead of time and rolls back/replays to reduce input lag. Very high system requirements."));
 
-  onVSyncChanged();
   onOptimalFramePacingChanged();
+  updateSkipDuplicateFramesEnabled();
   updateRewind();
 }
 
@@ -200,12 +209,6 @@ void EmulationSettingsWidget::onTurboSpeedIndexChanged(int index)
   m_dialog->setFloatSettingValue("Main", "TurboSpeed", okay ? value : 0.0f);
 }
 
-void EmulationSettingsWidget::onVSyncChanged()
-{
-  const bool vsync = m_dialog->getEffectiveBoolValue("Display", "VSync", false);
-  m_ui.syncToHostRefreshRate->setEnabled(vsync);
-}
-
 void EmulationSettingsWidget::onOptimalFramePacingChanged()
 {
   const bool optimal_frame_pacing_enabled = m_dialog->getEffectiveBoolValue("Display", "OptimalFramePacing", false);
@@ -221,6 +224,13 @@ void EmulationSettingsWidget::onPreFrameSleepChanged()
   m_ui.preFrameSleepBufferLabel->setVisible(show_buffer_size);
 }
 
+void EmulationSettingsWidget::updateSkipDuplicateFramesEnabled()
+{
+  const bool vsync = m_dialog->getEffectiveBoolValue("Display", "VSync", false);
+  const bool sync_to_host = m_dialog->getEffectiveBoolValue("Main", "SyncToHostRefreshRate", false) && vsync;
+  m_ui.skipPresentingDuplicateFrames->setEnabled(!sync_to_host);
+}
+
 void EmulationSettingsWidget::updateRewind()
 {
   const bool rewind_enabled = m_dialog->getEffectiveBoolValue("Main", "RewindEnable", false);

src/duckstation-qt/emulationsettingswidget.h

@@ -21,9 +21,9 @@ private Q_SLOTS:
   void onEmulationSpeedIndexChanged(int index);
   void onFastForwardSpeedIndexChanged(int index);
   void onTurboSpeedIndexChanged(int index);
-  void onVSyncChanged();
   void onOptimalFramePacingChanged();
   void onPreFrameSleepChanged();
+  void updateSkipDuplicateFramesEnabled();
   void updateRewind();
 
 private:

src/duckstation-qt/emulationsettingswidget.ui

@@ -68,10 +68,10 @@
       <string>Latency Control</string>
      </property>
      <layout class="QGridLayout" name="gridLayout">
-      <item row="0" column="0">
-       <widget class="QCheckBox" name="vsync">
+      <item row="1" column="1">
+       <widget class="QCheckBox" name="preFrameSleep">
         <property name="text">
-         <string>Vertical Sync (VSync)</string>
+         <string>Reduce Input Latency</string>
         </property>
        </widget>
       </item>
@@ -82,6 +82,13 @@
         </property>
        </widget>
       </item>
+      <item row="0" column="0">
+       <widget class="QCheckBox" name="vsync">
+        <property name="text">
+         <string>Vertical Sync (VSync)</string>
+        </property>
+       </widget>
+      </item>
       <item row="1" column="0">
        <widget class="QCheckBox" name="optimalFramePacing">
         <property name="text">
@@ -89,23 +96,23 @@
         </property>
        </widget>
       </item>
-      <item row="1" column="1">
-       <widget class="QCheckBox" name="preFrameSleep">
+      <item row="2" column="0">
+       <widget class="QCheckBox" name="skipPresentingDuplicateFrames">
         <property name="text">
-         <string>Reduce Input Latency</string>
+         <string>Skip Duplicate Frame Display</string>
         </property>
        </widget>
       </item>
-      <item row="2" column="0" colspan="2">
-       <layout class="QHBoxLayout" name="preFrameSleepBufferLayout" stretch="0,1">
-        <item>
+      <item row="2" column="1">
+       <layout class="QFormLayout" name="formLayout_3">
+        <item row="0" column="0">
          <widget class="QLabel" name="preFrameSleepBufferLabel">
           <property name="text">
            <string>Frame Time Buffer:</string>
           </property>
          </widget>
         </item>
-        <item>
+        <item row="0" column="1">
          <widget class="QDoubleSpinBox" name="preFrameSleepBuffer">
           <property name="suffix">
            <string> Milliseconds</string>