GCPadEmu: only connected if default device connected

This lets Dolphin know if a configured GameCube Controller should actually
be treated as connected or not.

Talked to @JMC47 a bit about this last night. My use-case is that all of
my controllers are the same hardware (Xbox One controllers) so share the
same configuration (modulo device number). Treating them all as always
connected isn't a problem for most games, but in some (Smash Bros.) it
forces me to go find a keyboard/mouse and unconfigure any controllers
that I don't actually have connected. Hotplugging devices (works on macOS,
at least) + this patch remove my need to ever touch the Controller Config
dialog while in a game.

This patch makes the following changes:

- A new `BooleanSetting` in `GCPadEmu` called "Always Connected", which
  defaults to false.
- `ControllerEmu` tracks whether the default device is connected on every
  call to `UpdateReferences()`.
- `GCPadEmu.GetStatus()` now sets err bit to `PAD_ERR_NO_CONTROLLER` if
  the default device isn't connected.
- `SIDevice_GCController` handles `PAD_ERR_NO_CONTROLLER` by imitating the
  behaviour of `SIDevice_Null` (as far as I can tell, this is the only use
  of the error bit from `GCPadStatus`).

I wanted to add an OSD message akin to the ones when Wiimotes get
connected/disconnected, but I haven't yet found where to put the logic.

Source/Core/Core/HW/GCPadEmu.cpp

@@ -83,6 +83,10 @@ GCPad::GCPad(const unsigned int index) : m_index(index)
 
   // options
   groups.emplace_back(m_options = new ControllerEmu::ControlGroup(_trans("Options")));
+  m_options->boolean_settings.emplace_back(
+      // i18n: Treat a controller as always being connected regardless of what
+      // devices the user actually has plugged in
+      m_always_connected = new ControllerEmu::BooleanSetting(_trans("Always Connected"), false));
   m_options->boolean_settings.emplace_back(std::make_unique<ControllerEmu::BooleanSetting>(
       _trans("Iterative Input"), false, ControllerEmu::SettingType::VIRTUAL));
 }
@@ -124,6 +128,12 @@ GCPadStatus GCPad::GetInput() const
   ControlState x, y, triggers[2];
   GCPadStatus pad = {};
 
+  if (!(m_always_connected->GetValue() || IsDefaultDeviceConnected()))
+  {
+    pad.isConnected = false;
+    return pad;
+  }
+
   // buttons
   m_buttons->GetState(&pad.button, button_bitmasks);
 

Source/Core/Core/HW/GCPadEmu.h

@@ -6,6 +6,7 @@
 
 #include <string>
 
+#include "InputCommon/ControllerEmu/ControlGroup/ControlGroup.h"
 #include "InputCommon/ControllerEmu/ControllerEmu.h"
 
 struct GCPadStatus;
@@ -14,7 +15,6 @@ namespace ControllerEmu
 {
 class AnalogStick;
 class Buttons;
-class ControlGroup;
 class MixedTriggers;
 }
 
@@ -54,6 +54,7 @@ private:
   ControllerEmu::ControlGroup* m_rumble;
   ControllerEmu::Buttons* m_mic;
   ControllerEmu::ControlGroup* m_options;
+  ControllerEmu::BooleanSetting* m_always_connected;
 
   const unsigned int m_index;
 

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

@@ -47,6 +47,14 @@ int CSIDevice_GCController::RunBuffer(u8* buffer, int length)
   // For debug logging only
   ISIDevice::RunBuffer(buffer, length);
 
+  GCPadStatus pad_status = GetPadStatus();
+  if (!pad_status.isConnected)
+  {
+    constexpr u32 reply = SI_ERROR_NO_RESPONSE;
+    std::memcpy(buffer, &reply, sizeof(reply));
+    return 4;
+  }
+
   // Read the command
   EBufferCommands command = static_cast<EBufferCommands>(buffer[3]);
 
@@ -165,6 +173,13 @@ GCPadStatus CSIDevice_GCController::GetPadStatus()
 bool CSIDevice_GCController::GetData(u32& hi, u32& low)
 {
   GCPadStatus pad_status = GetPadStatus();
+
+  if (!pad_status.isConnected)
+  {
+    hi = 0x80000000;
+    return true;
+  }
+
   if (HandleButtonCombos(pad_status) == COMBO_ORIGIN)
     pad_status.button |= PAD_GET_ORIGIN;