SI/GCSteeringWheel: Allow simultaneous use of accelerator and brake.

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

@@ -4,6 +4,8 @@
 
 #include "Core/HW/SI/SI_DeviceGCSteeringWheel.h"
 
+#include <algorithm>
+#include <cmath>
 #include <cstring>
 
 #include "Common/CommonTypes.h"
@@ -57,13 +59,37 @@ bool CSIDevice_GCSteeringWheel::GetData(u32& hi, u32& low)
     low = (u8)pad_status.triggerRight;              // All 8 bits
     low |= (u32)((u8)pad_status.triggerLeft << 8);  // All 8 bits
 
-    // The GC Steering Wheel appears to have combined pedals
+    // The GC Steering Wheel has 8 bit values for both the accelerator/brake.
-    // (both the Accelerate and Brake pedals are mapped to a single axis)
+    // Our mapping UI and GCPadEmu class weren't really designed to provide
-    // We use the stickY axis for the pedals.
+    // input data other than what the regular GC controller has.
-    if (pad_status.stickY < 128)
+    //
-      low |= (u32)((u8)(255 - ((pad_status.stickY & 0x7f) * 2)) << 16);  // All 8 bits (Brake)
+    // Without a big redesign we really don't have a choice but to
-    if (pad_status.stickY >= 128)
+    // use the analog stick values for accelerator/brake.
-      low |= (u32)((u8)((pad_status.stickY & 0x7f) * 2) << 24);  // All 8 bits (Accelerate)
+    //
+    // Main-stick: up:accelerator / down:brake
+    //
+    // But that doesn't allow the user to press both at the same time.
+    // so also provide the opposite functionality on the c-stick.
+    //
+    // C-stick: up:brake / down:accelerator
+
+    // Use either the upper-half of main-stick or lower-half of c-stick for accelerator.
+    const int accel_value = std::max(pad_status.stickY - GCPadStatus::MAIN_STICK_CENTER_Y,
+                                     GCPadStatus::C_STICK_CENTER_Y - pad_status.substickY);
+
+    // Use either the upper-half of c-stick or lower-half of main-stick for brake.
+    const int brake_value = std::max(pad_status.substickY - GCPadStatus::C_STICK_CENTER_Y,
+                                     GCPadStatus::MAIN_STICK_CENTER_Y - pad_status.stickY);
+
+    // We must double these values because we are mapping half of a stick range to a 0..255 value.
+    // We're only getting half the precison we could potentially have,
+    // but we'll have to redesign our gamecube controller input to fix that.
+
+    // All 8 bits (Accelerate)
+    low |= u32(std::clamp(accel_value * 2, 0, 0xff)) << 24;
+
+    // All 8 bits (Brake)
+    low |= u32(std::clamp(brake_value * 2, 0, 0xff)) << 16;
 
     HandleButtonCombos(pad_status);
   }