[Vulkan] Fix fullscreen corrupting HDR state on Windows

src/xenia/ui/vulkan/vulkan_device.cc

@@ -167,6 +167,11 @@ std::unique_ptr<VulkanDevice> VulkanDevice::CreateIfSupported(
   if (with_swapchain) {
     // #2.
     XE_UI_VULKAN_STRUCT_EXTENSION(KHR_swapchain)
+#if XE_PLATFORM_WIN32
+    // #256. Windows-only extension to control fullscreen exclusive behavior.
+    // Used to prevent HDR state corruption during fullscreen transitions.
+    XE_UI_VULKAN_STRUCT_EXTENSION(EXT_full_screen_exclusive)
+#endif
   }
 
   bool ext_1_2_KHR_sampler_mirror_clamp_to_edge = false;

src/xenia/ui/vulkan/vulkan_device.h

@@ -183,6 +183,10 @@ class VulkanDevice {
     bool ext_EXT_memory_budget = false;                 // #238
     // Has optional features not implied by this being true.
     bool ext_1_3_KHR_maintenance4 = false;  // #414
+#if XE_PLATFORM_WIN32
+    // VK_EXT_full_screen_exclusive (#256, Windows only)
+    bool ext_EXT_full_screen_exclusive = false;
+#endif
   };
 
   const Extensions& extensions() const { return extensions_; }

src/xenia/ui/vulkan/vulkan_presenter.cc

@@ -1142,6 +1142,22 @@ VkSwapchainKHR VulkanPresenter::PaintContext::CreateSwapchainForVulkanSurface(
   VkSwapchainCreateInfoKHR swapchain_create_info;
   swapchain_create_info.sType = VK_STRUCTURE_TYPE_SWAPCHAIN_CREATE_INFO_KHR;
   swapchain_create_info.pNext = nullptr;
+
+#if XE_PLATFORM_WIN32
+  // On Windows, use VK_EXT_full_screen_exclusive to explicitly disallow
+  // fullscreen exclusive mode. This prevents HDR state corruption when
+  // entering/exiting fullscreen, as the Windows compositor remains in control
+  // of the display state throughout the transition.
+  VkSurfaceFullScreenExclusiveInfoEXT full_screen_exclusive_info;
+  if (vulkan_device->extensions().ext_EXT_full_screen_exclusive) {
+    full_screen_exclusive_info.sType =
+        VK_STRUCTURE_TYPE_SURFACE_FULL_SCREEN_EXCLUSIVE_INFO_EXT;
+    full_screen_exclusive_info.pNext = nullptr;
+    full_screen_exclusive_info.fullScreenExclusive =
+        VK_FULL_SCREEN_EXCLUSIVE_DISALLOWED_EXT;
+    swapchain_create_info.pNext = &full_screen_exclusive_info;
+  }
+#endif
   swapchain_create_info.flags = 0;
   swapchain_create_info.surface = surface;
   swapchain_create_info.minImageCount =