Emulate flip when the primary surface is requested in system memory

When the primary surface chain is requested to be created in system memory,
flip should be emulated (copy from back buffer to front buffer) to be
consistent with legacy DirectDraw behavior.

Fixes flashing graphical artifacts in Carmageddon (Win95 version) menus
when exiting from a race, mentioned in issue #3.

DDrawCompat/DDraw/DirectDraw.cpp

@@ -122,20 +122,14 @@ namespace DDraw
 			return s_origVtable.CreateSurface(This, lpDDSurfaceDesc, lplpDDSurface, pUnkOuter);
 		}
 
-		HRESULT result = DD_OK;
+		if (lpDDSurfaceDesc->ddsCaps.dwCaps & DDSCAPS_PRIMARYSURFACE)
-
-		const bool isPrimary = 0 != (lpDDSurfaceDesc->ddsCaps.dwCaps & DDSCAPS_PRIMARYSURFACE);
-
-		if (isPrimary)
 		{
-			result = PrimarySurface::create<TDirectDraw>(*This, *lpDDSurfaceDesc, *lplpDDSurface);
+			return PrimarySurface::create<TDirectDraw>(*This, *lpDDSurfaceDesc, *lplpDDSurface);
 		}
 		else
 		{
-			result = Surface::create<TDirectDraw>(*This, *lpDDSurfaceDesc, *lplpDDSurface);
+			return Surface::create<TDirectDraw>(*This, *lpDDSurfaceDesc, *lplpDDSurface);
 		}
-
-		return result;
 	}
 
 	template <typename TDirectDraw>

DDrawCompat/DDraw/Surfaces/PrimarySurface.cpp

@@ -10,6 +10,7 @@ namespace
 	DDSURFACEDESC2 g_primarySurfaceDesc = {};
 	CompatWeakPtr<IDirectDrawSurface> g_gdiSurface = nullptr;
 	CompatWeakPtr<IDirectDrawSurface> g_primarySurface = nullptr;
+	bool g_isFlipEmulated = false;
 }
 
 namespace DDraw
@@ -25,6 +26,7 @@ namespace DDraw
 
 		g_gdiSurface = nullptr;
 		g_primarySurface = nullptr;
+		g_isFlipEmulated = false;
 		s_palette = nullptr;
 		s_surfaceBuffers.clear();
 		ZeroMemory(&s_paletteEntries, sizeof(s_paletteEntries));
@@ -67,6 +69,7 @@ namespace DDraw
 		CompatPtr<IDirectDrawSurface> surface1(Compat::queryInterface<IDirectDrawSurface>(surface));
 		g_gdiSurface = surface1;
 		g_primarySurface = surface1;
+		g_isFlipEmulated = 0 != (desc.ddsCaps.dwCaps & DDSCAPS_SYSTEMMEMORY);
 
 		ZeroMemory(&g_primarySurfaceDesc, sizeof(g_primarySurfaceDesc));
 		g_primarySurfaceDesc.dwSize = sizeof(g_primarySurfaceDesc);
@@ -127,6 +130,11 @@ namespace DDraw
 			Compat::queryInterface<IDirectDrawSurface7>(g_primarySurface.get()));
 	}
 
+	bool PrimarySurface::isFlipEmulated()
+	{
+		return g_isFlipEmulated;
+	}
+
 	void PrimarySurface::resizeBuffers(CompatRef<IDirectDrawSurface7> surface)
 	{
 		DDSCAPS2 flipCaps = {};

DDrawCompat/DDraw/Surfaces/PrimarySurface.h

@@ -20,6 +20,7 @@ namespace DDraw
 		static const DDSURFACEDESC2& getDesc();
 		static CompatPtr<IDirectDrawSurface7> getGdiSurface();
 		static CompatPtr<IDirectDrawSurface7> getPrimary();
+		static bool isFlipEmulated();
 
 		void updateGdiSurfacePtr(IDirectDrawSurface* flipTargetOverride);
 

DDrawCompat/DDraw/Surfaces/PrimarySurfaceImpl.cpp

@@ -80,19 +80,38 @@ namespace DDraw
 		}
 
 		HRESULT result = m_impl.Flip(This, lpDDSurfaceTargetOverride, dwFlags);
-		if (SUCCEEDED(result))
+		if (FAILED(result))
 		{
-			result = RealPrimarySurface::flip(dwFlags);
+			return result;
-			if (SUCCEEDED(result))
+		}
+
+		result = RealPrimarySurface::flip(dwFlags);
+		if (SUCCEEDED(result) && !PrimarySurface::isFlipEmulated())
+		{
+			static_cast<PrimarySurface*>(m_data)->updateGdiSurfacePtr(
+				CompatPtr<IDirectDrawSurface>::from(lpDDSurfaceTargetOverride));
+			return DD_OK;
+		}
+
+		undoFlip(This, lpDDSurfaceTargetOverride);
+
+		if (SUCCEEDED(result) && PrimarySurface::isFlipEmulated())
+		{
+			if (lpDDSurfaceTargetOverride)
 			{
-				static_cast<PrimarySurface*>(m_data)->updateGdiSurfacePtr(
+				s_origVtable.BltFast(This, 0, 0, lpDDSurfaceTargetOverride, nullptr, DDBLTFAST_WAIT);
-					CompatPtr<IDirectDrawSurface>::from(lpDDSurfaceTargetOverride));
 			}
 			else
 			{
-				undoFlip(This, lpDDSurfaceTargetOverride);
+				TDdsCaps caps = {};
+				caps.dwCaps = DDSCAPS_BACKBUFFER;
+				CompatPtr<TSurface> backBuffer;
+				s_origVtable.GetAttachedSurface(This, &caps, &backBuffer.getRef());
+
+				s_origVtable.BltFast(This, 0, 0, backBuffer, nullptr, DDBLTFAST_WAIT);
 			}
 		}
+
 		return result;
 	}
 

DDrawCompat/DDraw/Surfaces/SurfaceImpl.h

@@ -56,6 +56,8 @@ namespace DDraw
 	protected:
 		void undoFlip(TSurface* This, TSurface* targetOverride);
 
+		static const Vtable<TSurface>& s_origVtable;
+
 	private:
 		bool bltRetry(TSurface*& dstSurface, RECT*& dstRect,
 			TSurface*& srcSurface, RECT*& srcRect, bool isTransparentBlt,
@@ -63,7 +65,5 @@ namespace DDraw
 		bool prepareBltRetrySurface(TSurface*& surface, RECT*& rect,
 			const TSurfaceDesc& desc, bool isTransparentBlt, bool isCopyNeeded);
 		void replaceWithVidMemSurface(TSurface*& surface, RECT*& rect, const TSurfaceDesc& desc);
-
-		static const Vtable<TSurface>& s_origVtable;
 	};
 }