fix mode 4: stagger right MFD BeginScene to step 1 to match flip timing

Root cause of the broken MFD2 display: CMFD_Device::BeginScene() cleared
the right device back buffer at old sh_step==0, but with the stagger the
right device flip also fired in that same frame (new sh_step==1 = old
sh_step==0 after increment). The flip presented a just-cleared buffer
with only the grid, no channel data.

Fix: split BeginScene for mode 4 - left device (step 0) vs right device
(step 1). Add BeginSceneRight() called from WinMain at old sh_step==1.
The right device flip at new sh_step==1 (= old sh_step==0) now shows
channels 3-4 rendered at steps 5-6 of the previous cycle - correct.

Cycle for mode 4 with stagger:
  old sh_step 0: radar+left BeginScene, no flip
  new sh_step 1: flip right MFD (shows prev cycle channels 3-4)
  old sh_step 1: right BeginScene (clear+grid)
  old sh_step 2-4: channels 0-2 -> left device
  old sh_step 5-6: channels 3-4 -> right device
  new sh_step 0: flip radar+left MFD (shows prev cycle channels 0-2)

Gameleap/code/CoreTech/Libraries/GameOS/WinMain.cpp

@@ -941,10 +941,15 @@ void gos_UpdateDisplay( bool Everything )
 			}
 			break;
 		case 4:
-			// Same 7-step cadence as mode 1: clear both MFD devices at step 0.
+			// Step 0: clear + grid for radar and LEFT MFD.
+			// Step 1: clear + grid for RIGHT MFD (staggered so the right
+			//   flip at new sh_step==1 shows channels 3-4 from the previous
+			//   cycle, not a freshly-cleared buffer).
 			if(sh_step==0){
 				radar_device.BeginScene();
-				mfd_device.BeginScene();  // also clears mfd_device_right internally
+				mfd_device.BeginScene();  // left device only
+			} else if(sh_step==1) {
+				mfd_device.BeginSceneRight();  // right device clear + grid
 			}
 			break;
 		}

Gameleap/code/CoreTech/Libraries/GameOS/render.cpp

@@ -1620,23 +1620,15 @@ bool CMFD_Device::BeginScene()
 		//pD3DDevice->Clear(0,NULL,D3DCLEAR_TARGET ,0,1.0f,0);
 		}break;
 	case 4:
-		// Clear and draw background grid on the LEFT device.
+		// Clear and draw background grid on the LEFT device only.
+		// The right device is cleared/gridded in BeginSceneRight(),
+		// called from WinMain at old sh_step==1 (one frame after the
+		// right MFD flip) so its back buffer has fresh content when flipped.
 		SetRenderTargetBackbuffer();
 		pD3DDevice->Clear(0,NULL,D3DCLEAR_TARGET,0,1.0f,0);
 		pD3DDevice->BeginScene();
 		if(sh_game_started) DrawMFDBackGrid();
 		pD3DDevice->EndScene();
-		// Clear and draw background grid on the RIGHT device.
-		if (m_pRightDevice) {
-			m_pRightDevice->SetRenderTargetBackbuffer();
-			m_pRightDevice->pD3DDevice->Clear(0,NULL,D3DCLEAR_TARGET,0,1.0f,0);
-			m_pRightDevice->pD3DDevice->BeginScene();
-			if(sh_game_started) {
-				m_pRightDevice->pD3DDevice->SetTexture(0,0);
-				m_pRightDevice->DrawQuadList(8,rcs640_solo,0xFFFFFFFF);
-			}
-			m_pRightDevice->pD3DDevice->EndScene();
-		}
 		return true;  // skip the common BeginScene/DrawGrid/EndScene below
 	}
 	pD3DDevice->BeginScene();
@@ -1655,6 +1647,25 @@ bool CMFD_Device::EndScene()
 	return true;
 }
 
+// Mode 4: clear and draw the background grid on the right device.
+// Called from WinMain at old sh_step==1, one frame after the right MFD
+// flip, so channels 3-4 can render into a fresh back buffer before the
+// next flip at new sh_step==1 (= old sh_step==0).
+bool CMFD_Device::BeginSceneRight()
+{
+	if (g_nTypeOfMFDs != 4 || !m_pRightDevice)
+		return false;
+	m_pRightDevice->SetRenderTargetBackbuffer();
+	m_pRightDevice->pD3DDevice->Clear(0,NULL,D3DCLEAR_TARGET,0,1.0f,0);
+	m_pRightDevice->pD3DDevice->BeginScene();
+	if(sh_game_started) {
+		m_pRightDevice->pD3DDevice->SetTexture(0,0);
+		m_pRightDevice->DrawQuadList(8,rcs640_solo,0xFFFFFFFF);
+	}
+	m_pRightDevice->pD3DDevice->EndScene();
+	return true;
+}
+
 
 bool CMFD_Device::Release()
 {

Gameleap/code/CoreTech/Libraries/GameOS/render.hpp

@@ -178,6 +178,7 @@ public:
 	bool BeginChannel(DWORD channel);// 0~4번의 채널을 정할 수 있게된다.
 	bool EndChannel();
 	virtual bool BeginScene();		//normal한 beginscene/endscene를 한다.
+	bool BeginSceneRight();		// mode 4: clear+grid on right device at sh_step==1
 	virtual bool EndScene();		//flip을 한다.
 	virtual bool Release();
 	bool LoadDamageTexture(const char *mechtexturename);