Throw from Device::UpdateDevice when rendering is enabled

Apps/UnitTests/Source/Tests.Device.D3D11.cpp

@@ -6,6 +6,8 @@
 
 #include <winrt/base.h>
 
+extern Babylon::Graphics::Configuration g_deviceConfig;
+
 namespace
 {
     winrt::com_ptr<ID3D11Device> CreateDevice()
@@ -101,3 +103,26 @@ TEST(Device, BackBuffer)
         device.FinishRenderingCurrentFrame();
     }
 }
+
+// Verifies that UpdateDevice throws when called while rendering is enabled.
+TEST(Device, UpdateDeviceThrowsWhenRenderingEnabled)
+{
+    winrt::com_ptr<ID3D11Device> d3dDevice = CreateDevice();
+
+    Babylon::Graphics::Configuration config = g_deviceConfig;
+    config.Device = d3dDevice.get();
+
+    Babylon::Graphics::Device device{config};
+
+    // Permitted before EnableRendering.
+    EXPECT_NO_THROW(device.UpdateDevice(d3dDevice.get()));
+
+    // StartRenderingCurrentFrame triggers EnableRendering -> throws.
+    device.StartRenderingCurrentFrame();
+    EXPECT_THROW(device.UpdateDevice(d3dDevice.get()), std::runtime_error);
+    device.FinishRenderingCurrentFrame();
+
+    // Permitted again after DisableRendering.
+    device.DisableRendering();
+    EXPECT_NO_THROW(device.UpdateDevice(d3dDevice.get()));
+}

Core/Graphics/Include/Shared/Babylon/Graphics/Device.h

@@ -112,7 +112,15 @@ namespace Babylon::Graphics
         // method and structure might change.
 
         void UpdateWindow(WindowT window);
+
+        // Sets the underlying graphics device used for rendering. The new device takes effect on
+        // the next EnableRendering call.
+        //
+        // Only valid when rendering is disabled -- i.e. before the first EnableRendering /
+        // StartRenderingCurrentFrame call, or after a DisableRendering call. Throws
+        // std::runtime_error otherwise.
         void UpdateDevice(DeviceT device);
+
         void UpdateSize(size_t width, size_t height);
         void UpdateMSAA(uint8_t value);
         void UpdateAlphaPremultiplied(bool enabled);

Core/Graphics/Source/DeviceImpl.cpp

@@ -108,6 +108,10 @@ namespace Babylon::Graphics
     void DeviceImpl::UpdateDevice(DeviceT device)
     {
         std::scoped_lock lock{m_state.Mutex};
+        if (m_state.Bgfx.Initialized)
+        {
+            throw std::runtime_error{"UpdateDevice called while rendering is enabled."};
+        }
         m_state.Bgfx.InitState.platformData.context = device;
         m_state.Bgfx.Dirty = true;
     }