Make the clean room process replace the splash screen with its own.

This is required to get Windows to automatically transfer foreground focus so that the BA's window or the elevation prompt is automatically activated.

Fixes 6836

3 files changed, 21 insertions, 2 deletions

diff --git a/src/burn/engine/engine.cpp b/src/burn/engine/engine.cpp
index 413db69b..334ea23b 100644
--- a/src/burn/engine/engine.cpp
+++ b/src/burn/engine/engine.cpp
@@ -132,7 +132,7 @@ extern "C" HRESULT EngineRun(
 
     engineState.command.nCmdShow = nCmdShow;
 
-    if (BURN_MODE_ELEVATED != engineState.internalCommand.mode && BOOTSTRAPPER_DISPLAY_NONE < engineState.command.display && !engineState.command.hwndSplashScreen)
+    if (BURN_MODE_ELEVATED != engineState.internalCommand.mode && BOOTSTRAPPER_DISPLAY_NONE < engineState.command.display)
     {
         SplashScreenCreate(hInstance, NULL, &engineState.command.hwndSplashScreen);
     }
diff --git a/src/burn/engine/splashscreen.cpp b/src/burn/engine/splashscreen.cpp
index 7ba4e630..d8618feb 100644
--- a/src/burn/engine/splashscreen.cpp
+++ b/src/burn/engine/splashscreen.cpp
@@ -13,6 +13,7 @@ struct SPLASHSCREEN_INFO
     SIZE size;
     UINT nDpi;
     HWND hWnd;
+    HWND hwndPrevious;
 };
 
 struct SPLASHSCREEN_CONTEXT
@@ -258,6 +259,19 @@ static LRESULT CALLBACK WndProc(
     case WM_ERASEBKGND:
         OnEraseBkgnd(pSplashScreen, wParam);
         return 1;
+
+    case WM_ENTERIDLE:
+        lres = ::DefWindowProcW(hWnd, uMsg, wParam, lParam);
+
+        // We had to create our own splash screen so that Windows would automatically transfer focus from the other process's splash screen.
+        // Try to make sure new splash screen has painted before closing old one to avoid flickering.
+        if (pSplashScreen->hwndPrevious)
+        {
+            ::PostMessageW(pSplashScreen->hwndPrevious, WM_CLOSE, 0, 0);
+            pSplashScreen->hwndPrevious = NULL;
+        }
+
+        return lres;
     }
 
     return ::DefWindowProcW(hWnd, uMsg, wParam, lParam);
@@ -276,6 +290,11 @@ static HRESULT LoadSplashScreen(
     DPIU_MONITOR_CONTEXT* pMonitorContext = NULL;
     RECT* pMonitorRect = NULL;
 
+    if (::IsWindow(*pContext->pHwnd))
+    {
+        pSplashScreen->hwndPrevious = *pContext->pHwnd;
+    }
+
     pSplashScreen->nDpi = USER_DEFAULT_SCREEN_DPI;
     pSplashScreen->hBitmap = ::LoadBitmapW(pContext->hInstance, MAKEINTRESOURCEW(pContext->pSplashScreenConfiguration->wResourceId));
     ExitOnNullWithLastError(pSplashScreen->hBitmap, hr, "Failed to load splash screen bitmap.");
diff --git a/src/test/burn/WixToolsetTest.BurnE2E/WixIuiBaTests.cs b/src/test/burn/WixToolsetTest.BurnE2E/WixIuiBaTests.cs
index 18dd41db..3e7e3ded 100644
--- a/src/test/burn/WixToolsetTest.BurnE2E/WixIuiBaTests.cs
+++ b/src/test/burn/WixToolsetTest.BurnE2E/WixIuiBaTests.cs
@@ -114,7 +114,7 @@ namespace WixToolsetTest.BurnE2E
         // Manual test for InternalUIBundle:
         //  1. Double click InternalUIBundle.exe on a machine that will prompt for elevation.
         //  2. Verify that the splash screen appeared but the prereq BA did not come up.
-        //  3. Verify that the elevation prompt came up immediately instead of flashing on the taskbar. (This is currently broken)
+        //  3. Verify that the elevation prompt came up immediately instead of flashing on the taskbar.
         //  4. Allow elevation.
         //  5. Verify that the MSI UI came up and the splash screen disappeared.
         //  6. Accept the two CA messages and click the install button.