NetPlay: Change "Reduce Polling Rate" to poll twice per frame

Some games don't play nice when we poll only once per frame, so we'll poll twice instead.

Source/Core/Core/HW/SI/SI.cpp

@@ -11,8 +11,6 @@
 
 #include "Common/ChunkFile.h"
 #include "Common/CommonTypes.h"
-#include "Common/Config/Config.h"
-#include "Core/Config/MainSettings.h"
 #include "Core/ConfigManager.h"
 #include "Core/CoreTiming.h"
 #include "Core/HW/MMIO.h"
@@ -624,11 +622,7 @@ SIDevices GetDeviceType(int channel)
 
 u32 GetPollXLines()
 {
-  // Returning 0 here effectively makes polling happen once per frame, as this is used to increment
-  // a value in VI for when the next SI poll happens. This should normally only be set during
-  // NetPlay, as it does not matter for a non-networked session. However, it may also be set during
-  // movie playback for movies recorded during NetPlay.
-  return Config::Get(Config::MAIN_REDUCE_POLLING_RATE) ? 0 : s_poll.X;
+  return s_poll.X;
 }
 
 }  // end of namespace SerialInterface

Source/Core/Core/HW/VideoInterface.cpp

@@ -14,6 +14,7 @@
 #include "Common/Logging/Log.h"
 #include "Common/MathUtil.h"
 
+#include "Core/Config/MainSettings.h"
 #include "Core/Config/SYSCONFSettings.h"
 #include "Core/ConfigManager.h"
 #include "Core/Core.h"
@@ -731,7 +732,13 @@ void Update(u64 ticks)
   if (s_half_line_of_next_si_poll == s_half_line_count)
   {
     SerialInterface::UpdateDevices();
-    s_half_line_of_next_si_poll += SerialInterface::GetPollXLines();
+
+    // If this setting is enabled, only poll twice per field instead of what the game wanted. It may
+    // be set during NetPlay or Movie playback.
+    if (Config::Get(Config::MAIN_REDUCE_POLLING_RATE))
+      s_half_line_of_next_si_poll += GetHalfLinesPerEvenField() / 2;
+    else
+      s_half_line_of_next_si_poll += SerialInterface::GetPollXLines();
   }
   if (s_half_line_count == s_even_field_first_hl)
   {
@@ -819,4 +826,4 @@ void FakeVIUpdate(u32 xfb_address, u32 fb_width, u32 fb_height)
   }
 }
 
-}  // namespace
+}  // namespace VideoInterface

Source/Core/DolphinQt/NetPlay/NetPlayDialog.cpp

@@ -123,8 +123,8 @@ void NetPlayDialog::CreateMainLayout()
   m_md5_button->setMenu(menu);
 
   m_reduce_polling_rate_box->setToolTip(
-      tr("This will reduce bandwidth usage, but may add up to one frame of additional latency, as "
-         "controllers will be polled only once per frame."));
+      tr("This will reduce bandwidth usage by polling GameCube controllers only twice per frame. "
+         "Does not affect Wii Remotes."));
 
   m_main_layout->addWidget(m_game_button, 0, 0);
   m_main_layout->addWidget(m_md5_button, 0, 1);