Add a fallback to software rendering (#1263)

This commit enables a software rendering fallback for the DX renderer in the case that hardware acceleration fails. This is primarily useful for Hyper-V environments where hardware acceleration is not guaranteed to exist.

This will be useful for future work to enable the DX renderer to run on windows 7 since win7 virtual machines do not/cannot have hardware acceleration unlike windows 10 machines

This commit does two things:
- Fallback to `D3D_DRIVER_TYPE_WARP` if `D3D_DRIVER_TYPE_HARDWARE` fails.
- pass `NULL` as the adapter instead of creating the default adapter ourselves.

src/renderer/dx/DxRenderer.cpp

@@ -130,8 +130,6 @@ DxEngine::~DxEngine()
 
     RETURN_IF_FAILED(CreateDXGIFactory1(IID_PPV_ARGS(&_dxgiFactory2)));
 
-    RETURN_IF_FAILED(_dxgiFactory2->EnumAdapters1(0, &_dxgiAdapter1));
-
     const DWORD DeviceFlags = D3D11_CREATE_DEVICE_BGRA_SUPPORT |
                               // clang-format off
         // This causes problems for folks who do not have the whole DirectX SDK installed
@@ -154,18 +152,33 @@ DxEngine::~DxEngine()
         D3D_FEATURE_LEVEL_9_1,
     };
 
-    RETURN_IF_FAILED(D3D11CreateDevice(_dxgiAdapter1.Get(),
-                                       D3D_DRIVER_TYPE_UNKNOWN,
-                                       NULL,
-                                       DeviceFlags,
-                                       FeatureLevels,
-                                       ARRAYSIZE(FeatureLevels),
-                                       D3D11_SDK_VERSION,
-                                       &_d3dDevice,
-                                       NULL,
-                                       &_d3dDeviceContext));
-
-    RETURN_IF_FAILED(_dxgiAdapter1->EnumOutputs(0, &_dxgiOutput));
+    // Trying hardware first for maximum performance, then trying WARP (software) renderer second
+    // in case we're running inside a downlevel VM where hardware passthrough isn't enabled like
+    // for Windows 7 in a VM.
+    const auto hardwareResult = D3D11CreateDevice(NULL,
+                                                  D3D_DRIVER_TYPE_HARDWARE,
+                                                  NULL,
+                                                  DeviceFlags,
+                                                  FeatureLevels,
+                                                  ARRAYSIZE(FeatureLevels),
+                                                  D3D11_SDK_VERSION,
+                                                  &_d3dDevice,
+                                                  NULL,
+                                                  &_d3dDeviceContext);
+
+    if (FAILED(hardwareResult))
+    {
+        RETURN_IF_FAILED(D3D11CreateDevice(NULL,
+                                           D3D_DRIVER_TYPE_WARP,
+                                           NULL,
+                                           DeviceFlags,
+                                           FeatureLevels,
+                                           ARRAYSIZE(FeatureLevels),
+                                           D3D11_SDK_VERSION,
+                                           &_d3dDevice,
+                                           NULL,
+                                           &_d3dDeviceContext));
+    }
 
     _displaySizePixels = _GetClientSize();
 
@@ -309,7 +322,6 @@ void DxEngine::_ReleaseDeviceResources() noexcept
 
     _dxgiSurface.Reset();
     _dxgiSwapChain.Reset();
-    _dxgiOutput.Reset();
 
     if (nullptr != _d3dDeviceContext.Get())
     {
@@ -321,7 +333,6 @@ void DxEngine::_ReleaseDeviceResources() noexcept
 
     _d3dDevice.Reset();
 
-    _dxgiAdapter1.Reset();
     _dxgiFactory2.Reset();
 }
 

src/renderer/dx/DxRenderer.hpp

@@ -156,9 +156,7 @@ namespace Microsoft::Console::Render
         bool _haveDeviceResources;
         ::Microsoft::WRL::ComPtr<ID3D11Device> _d3dDevice;
         ::Microsoft::WRL::ComPtr<ID3D11DeviceContext> _d3dDeviceContext;
-        ::Microsoft::WRL::ComPtr<IDXGIAdapter1> _dxgiAdapter1;
         ::Microsoft::WRL::ComPtr<IDXGIFactory2> _dxgiFactory2;
-        ::Microsoft::WRL::ComPtr<IDXGIOutput> _dxgiOutput;
         ::Microsoft::WRL::ComPtr<IDXGISurface> _dxgiSurface;
         ::Microsoft::WRL::ComPtr<ID2D1RenderTarget> _d2dRenderTarget;
         ::Microsoft::WRL::ComPtr<ID2D1SolidColorBrush> _d2dBrushForeground;