[d3d9] Add option for extra frame buffer to fix GetFrameBufferData

dxvk.conf

@@ -765,6 +765,14 @@
 
 # d3d9.countLosableResources = True
 
+# Add an extra frame buffer when necessary
+#
+# Some games create a swapchain with only 1 buffer and still expect GetFrontBufferData() to correctly return back the data of the last present.
+# To make that work correctly, we add a second buffer and copy to it every single frame.
+# This is unnecessary for all but a single modded game (Silent Hill 2 Enhanced Edition), that's why it's a config option.
+
+# d3d9.extraFrontbuffer = False
+
 # Dref scaling for DXS0/FVF
 #
 # Some early D3D8 games expect Dref (depth texcoord Z) to be on the range of
@@ -843,4 +851,3 @@
 # - True/False
 
 # d3d8.forceLegacyDiscard = False
-

src/d3d9/d3d9_options.cpp

@@ -75,6 +75,7 @@ namespace dxvk {
     this->clampNegativeLodBias          = config.getOption<bool>        ("d3d9.clampNegativeLodBias",          false);
     this->countLosableResources         = config.getOption<bool>        ("d3d9.countLosableResources",         true);
     this->reproducibleCommandStream     = config.getOption<bool>        ("d3d9.reproducibleCommandStream",     false);
+    this->extraFrontbuffer              = config.getOption<bool>        ("d3d9.extraFrontbuffer",              false);
 
     // D3D8 options
     this->drefScaling                   = config.getOption<int32_t>     ("d3d8.scaleDref",                     0);

src/d3d9/d3d9_options.h

@@ -151,6 +151,9 @@ namespace dxvk {
 
     /// Enable depth texcoord Z (Dref) scaling (D3D8 quirk)
     int32_t drefScaling;
+
+    /// Add an extra front buffer to make GetFrontBufferData() work correctly when the swapchain only has a single buffer
+    bool extraFrontbuffer;
   };
 
 }

src/d3d9/d3d9_swapchain.cpp

@@ -167,8 +167,27 @@ namespace dxvk {
     UpdatePresentRegion(pSourceRect, pDestRect);
     UpdatePresentParameters();
 
+    if (!SwapWithFrontBuffer() && m_parent->GetOptions()->extraFrontbuffer) {
+      // We never actually rotate in the front buffer.
+      // Just blit to it for GetFrontBufferData.
+
+      // When we have multiple buffers, the last buffer always acts as the front buffer.
+      // (See comment in PresentImage for an explaination why.)
+      // Games with a buffer count of 1 rely on the contents of the previous frame still
+      // being there, so we can't just add another buffer to the rotation.
+      // At the same time, they could call GetFrontBufferData after already rendering to the backbuffer.
+      // So we have to do a copy of the backbuffer that will be copied to the Vulkan backbuffer
+      // and keep that around for the next frame.
+
+      const auto& backbuffer = m_backBuffers[0];
+      const auto& frontbuffer = GetFrontBuffer();
+      if (FAILED(m_parent->StretchRect(backbuffer.ptr(), nullptr, frontbuffer.ptr(), nullptr, D3DTEXF_NONE))) {
+        Logger::err("Failed to blit to front buffer");
+      }
+    }
+
 #ifdef _WIN32
-    const bool useGDIFallback = m_partialCopy && !HasFrontBuffer();
+    const bool useGDIFallback = m_partialCopy && !SwapWithFrontBuffer();
     if (useGDIFallback)
       return PresentImageGDI(m_window);
 #endif
@@ -916,7 +935,17 @@ namespace dxvk {
 
     // Rotate swap chain buffers so that the back
     // buffer at index 0 becomes the front buffer.
-    for (uint32_t i = 1; i < m_backBuffers.size(); i++)
+    uint32_t rotatingBufferCount = m_backBuffers.size();
+    if (!SwapWithFrontBuffer() && m_parent->GetOptions()->extraFrontbuffer) {
+      // The front buffer only exists for GetFrontBufferData
+      // and the application cannot obserse buffer swapping in GetBackBuffer()
+      rotatingBufferCount -= 1;
+    }
+
+    // Backbuffer 0 is the one that gets copied to the Vulkan swapchain backbuffer.
+    // => m_backBuffers[1] is the next one that gets presented
+    // and the currente m_backBuffers[0] ends up at the end of the vector.
+    for (uint32_t i = 1; i < rotatingBufferCount; i++)
       m_backBuffers[i]->Swap(m_backBuffers[i - 1].ptr());
 
     m_parent->m_flags.set(D3D9DeviceFlag::DirtyFramebuffer);
@@ -986,10 +1015,10 @@ namespace dxvk {
     // creating a new one to free up resources
     DestroyBackBuffers();
 
-    int NumFrontBuffer = HasFrontBuffer() ? 1 : 0;
-    const uint32_t NumBuffers = NumBackBuffers + NumFrontBuffer;
+    int frontBufferCount = (SwapWithFrontBuffer() || m_parent->GetOptions()->extraFrontbuffer) ? 1 : 0;
+    const uint32_t bufferCount = NumBackBuffers + frontBufferCount;
 
-    m_backBuffers.reserve(NumBuffers);
+    m_backBuffers.reserve(bufferCount);
 
     // Create new back buffer
     D3D9_COMMON_TEXTURE_DESC desc;
@@ -1010,7 +1039,7 @@ namespace dxvk {
     // we might need to lock for the BlitGDI fallback path
     desc.IsLockable         = true;
 
-    for (uint32_t i = 0; i < NumBuffers; i++) {
+    for (uint32_t i = 0; i < bufferCount; i++) {
       D3D9Surface* surface;
       try {
         surface = new D3D9Surface(m_parent, &desc, m_parent->IsExtended(), this, nullptr);

src/d3d9/d3d9_swapchain.h

@@ -240,17 +240,19 @@ namespace dxvk {
     bool IsDeviceReset(D3D9WindowContext* wctx);
 
     const Com<D3D9Surface, false>& GetFrontBuffer() const {
+      // Buffer 0 is the one that gets copied to the Vulkan backbuffer.
+      // We rotate buffers after presenting, so buffer 0 becomes the last buffer in the vector.
       return m_backBuffers.back();
     }
 
-    bool HasFrontBuffer() const {
+    bool SwapWithFrontBuffer() const {
       if (m_presentParams.SwapEffect == D3DSWAPEFFECT_COPY)
         return false;
 
       if (m_presentParams.SwapEffect == D3DSWAPEFFECT_COPY_VSYNC)
         return false;
 
-      // Tests show that SWAPEEFFECT_DISCARD + 1 backbuffer in windowed mode behaves identically to SWAPEFFECT_COPY
+      // Tests show that SWAPEEFFECT_DISCARD with 1 backbuffer in windowed mode behaves identically to SWAPEFFECT_COPY
       // For SWAPEFFECT_COPY we don't swap buffers but do another blit to the front buffer instead.
       if (m_presentParams.SwapEffect == D3DSWAPEFFECT_DISCARD && m_presentParams.BackBufferCount == 1 && m_presentParams.Windowed)
         return false;