Fix D3D12 pixel history MSAA test issues.

* Add missing resource transitions for the dispatch copy to fix
validation issues encountered while running the test.
* Adjust the component mapping to fix stencil copies failing to output
anything, which manifested as the fragment only showing one primitive
without correct output data.

renderdoc/driver/d3d12/d3d12_pixelhistory.cpp

@@ -391,6 +391,9 @@ void D3D12DebugManager::PixelHistoryCopyPixel(ID3D12GraphicsCommandListX *cmd,
       p.multisampled ? D3D12_SRV_DIMENSION_TEXTURE2DMS : D3D12_SRV_DIMENSION_TEXTURE2D;
   srvDesc.Format = p.srcImageFormat;
   srvDesc.Shader4ComponentMapping = D3D12_DEFAULT_SHADER_4_COMPONENT_MAPPING;
+  // multisample SRVs don't have a specifier for plane slice, use the component mapping instead.
+  if(p.multisampled && p.planeSlice == 1)
+    srvDesc.Shader4ComponentMapping = D3D12_ENCODE_SHADER_4_COMPONENT_MAPPING(1, 1, 1, 1);
   if(!p.multisampled)
   {
     srvDesc.Texture2D.MipLevels = 1;
@@ -596,8 +599,27 @@ struct D3D12PixelHistoryCallback : public D3D12ActionCallback
     // copy using a compute shader into a staging image first
     if(p.multisampled)
     {
-      // TODO: Is a resource transition needed here?
+      // For pipeline barriers.
+      D3D12_RESOURCE_BARRIER barriers[2] = {};
+      barriers[0] = barrier;
+      barriers[0].Transition.StateAfter = D3D12_RESOURCE_STATE_NON_PIXEL_SHADER_RESOURCE;
+      // Validation will complain if we don't transition all subresources for an SRV.
+      barriers[0].Transition.Subresource = D3D12_RESOURCE_BARRIER_ALL_SUBRESOURCES;
+
+      barriers[1].Type = D3D12_RESOURCE_BARRIER_TYPE_TRANSITION;
+      barriers[1].Flags = D3D12_RESOURCE_BARRIER_FLAG_NONE;
+      barriers[1].Transition.pResource = m_CallbackInfo.dstBuffer;
+      barriers[1].Transition.StateBefore = D3D12_RESOURCE_STATE_COPY_DEST;
+      barriers[1].Transition.StateAfter = D3D12_RESOURCE_STATE_UNORDERED_ACCESS;
+      barriers[1].Transition.Subresource = 0;
+
+      cmd->ResourceBarrier(2, barriers);
+
       m_pDevice->GetDebugManager()->PixelHistoryCopyPixel(cmd, m_CallbackInfo.dstBuffer, p, offset);
+
+      std::swap(barriers[0].Transition.StateBefore, barriers[0].Transition.StateAfter);
+      std::swap(barriers[1].Transition.StateBefore, barriers[1].Transition.StateAfter);
+      cmd->ResourceBarrier(2, barriers);
     }
     else
     {