[D3D9] Fix for back buffer data loss during D3D9 present. (#16)

Acording to the D3D9 spec the content of the back buffer can be altered only if the SwapEffect is D3DSWAPEFFECT_DISCARD. The current implementation of the front buffer caused the previous back buffers to have their content lost.

This change keeps a similar present back buffer swapping logic for D3DSWAPEFFECT_DISCARD. For other swap effects the front buffer is a copy of the last presented back buffer.

src/d3d9/d3d9_options.cpp

@@ -48,7 +48,6 @@ namespace dxvk {
     this->strictPow                     = config.getOption<bool>        ("d3d9.strictPow",                     true);
     this->lenientClear                  = config.getOption<bool>        ("d3d9.lenientClear",                  false);
     this->numBackBuffers                = config.getOption<int32_t>     ("d3d9.numBackBuffers",                0);
-    this->noExplicitFrontBuffer         = config.getOption<bool>        ("d3d9.noExplicitFrontBuffer",         false);
     this->deferSurfaceCreation          = config.getOption<bool>        ("d3d9.deferSurfaceCreation",          false);
     this->samplerAnisotropy             = config.getOption<int32_t>     ("d3d9.samplerAnisotropy",             -1);
     this->maxAvailableMemory            = config.getOption<int32_t>     ("d3d9.maxAvailableMemory",            4096);

src/d3d9/d3d9_swapchain.cpp

@@ -172,7 +172,7 @@ namespace dxvk {
       return D3DERR_INVALIDCALL;
 
     D3D9CommonTexture* dstTexInfo = dst->GetCommonTexture();
-    D3D9CommonTexture* srcTexInfo = m_backBuffers.back()->GetCommonTexture();
+    D3D9CommonTexture* srcTexInfo = m_frontBuffer->GetCommonTexture();
 
     if (unlikely(dstTexInfo->Desc()->Pool != D3DPOOL_SYSTEMMEM && dstTexInfo->Desc()->Pool != D3DPOOL_SCRATCH))
       return D3DERR_INVALIDCALL;
@@ -673,6 +673,24 @@ namespace dxvk {
       m_context->beginRecording(
         m_device->createCommandList());
 
+      if (m_presentParams.SwapEffect != D3DSWAPEFFECT_DISCARD)
+      {
+        VkOffset3D srcOffset = { int32_t(m_srcRect.left), int32_t(m_srcRect.top), 0 };
+        VkOffset3D dstOffset = { int32_t(m_dstRect.left), int32_t(m_dstRect.top), 0 };
+        VkImageSubresourceLayers singleLayerSubresource = { VK_IMAGE_ASPECT_COLOR_BIT, 0, 0, 1 };
+        VkExtent3D copyExtent =
+          { uint32_t(m_dstRect.right - m_dstRect.left), uint32_t(m_dstRect.bottom - m_dstRect.top), 0 };
+
+        m_context->copyImage(
+          m_frontBuffer->GetCommonTexture()->GetImage(),
+          singleLayerSubresource,
+          srcOffset,
+          swapImage,
+          singleLayerSubresource,
+          dstOffset,
+          copyExtent);
+      }
+
       VkRect2D srcRect = {
         {  int32_t(m_srcRect.left),                    int32_t(m_srcRect.top)                    },
         { uint32_t(m_srcRect.right - m_srcRect.left), uint32_t(m_srcRect.bottom - m_srcRect.top) } };
@@ -701,6 +719,11 @@ namespace dxvk {
     for (uint32_t i = 1; i < m_backBuffers.size(); i++)
       m_backBuffers[i]->Swap(m_backBuffers[i - 1].ptr());
 
+    // For swap discard do not copy the content to the front buffer
+    // but replace the front buffer reference with the last back buffer.
+    if (m_presentParams.SwapEffect == D3DSWAPEFFECT_DISCARD)
+      m_backBuffers.back()->Swap(m_frontBuffer.ptr());
+
     m_parent->m_flags.set(D3D9DeviceFlag::DirtyFramebuffer);
   }
 
@@ -840,6 +863,9 @@ namespace dxvk {
       backBuffer->ClearContainer();
 
     m_backBuffers.clear();
+
+    if (m_frontBuffer != nullptr)
+      m_frontBuffer->ClearContainer();
   }
 
 
@@ -848,8 +874,7 @@ namespace dxvk {
     // creating a new one to free up resources
     DestroyBackBuffers();
 
-    int NumFrontBuffer = m_parent->GetOptions()->noExplicitFrontBuffer ? 0 : 1;
-    m_backBuffers.resize(NumBackBuffers + NumFrontBuffer);
+    m_backBuffers.resize(NumBackBuffers);
 
     // Create new back buffer
     D3D9_COMMON_TEXTURE_DESC desc;
@@ -867,8 +892,17 @@ namespace dxvk {
     desc.IsBackBuffer       = TRUE;
     desc.IsAttachmentOnly   = FALSE;
 
-    for (uint32_t i = 0; i < m_backBuffers.size(); i++)
-      m_backBuffers[i] = new D3D9Surface(m_parent, &desc, this, nullptr);
+    try {
+      for (uint32_t i = 0; i < m_backBuffers.size(); i++)
+        m_backBuffers[i] = new D3D9Surface(m_parent, &desc, this, nullptr);
+
+      // Create an additional hidden front buffer.
+      m_frontBuffer = new D3D9Surface(m_parent, &desc, this, nullptr);
+    }
+    catch (const DxvkError& e) {
+      Logger::err(e.message());
+      return D3DERR_OUTOFVIDEOMEMORY;
+    })
 
     auto swapImage = m_backBuffers[0]->GetCommonTexture()->GetImage();
 
@@ -890,6 +924,10 @@ namespace dxvk {
         subresources, VK_IMAGE_LAYOUT_UNDEFINED);
     }
 
+    m_context->initImage(
+        m_frontBuffer->GetCommonTexture()->GetImage(),
+        subresources, VK_IMAGE_LAYOUT_UNDEFINED);
+
     m_device->submitCommandList(
       m_context->endRecording());
   }