Prefer OpenXR for desktop XR policy

src/platform_api/platform_policy.cpp

@@ -23,6 +23,34 @@ PlatformFamily current_platform_family() noexcept
 #endif
 }
 
+const char* xr_runtime_backend_name(XrRuntimeBackend backend) noexcept
+{
+    switch (backend)
+    {
+    case XrRuntimeBackend::openxr:
+        return "openxr";
+    case XrRuntimeBackend::openvr:
+        return "openvr";
+    case XrRuntimeBackend::none:
+    default:
+        return "none";
+    }
+}
+
+XrRuntimeSelection select_desktop_xr_runtime(
+    bool openxr_available,
+    bool openvr_available,
+    bool allow_legacy_openvr_fallback) noexcept
+{
+    if (openxr_available)
+        return { XrRuntimeBackend::openxr, false };
+
+    if (allow_legacy_openvr_fallback && openvr_available)
+        return { XrRuntimeBackend::openvr, true };
+
+    return {};
+}
+
 bool platform_deletes_recorded_files_on_clear(PlatformFamily family) noexcept
 {
     return family == PlatformFamily::ios || family == PlatformFamily::macos;

src/platform_api/platform_policy.h

@@ -17,8 +17,25 @@ enum class PlatformFamily {
     webgl,
 };
 
+enum class XrRuntimeBackend {
+    none,
+    openxr,
+    openvr,
+};
+
+struct XrRuntimeSelection {
+    XrRuntimeBackend backend = XrRuntimeBackend::none;
+    bool uses_legacy_openvr_fallback = false;
+};
+
 [[nodiscard]] PlatformFamily current_platform_family() noexcept;
 
+[[nodiscard]] const char* xr_runtime_backend_name(XrRuntimeBackend backend) noexcept;
+[[nodiscard]] XrRuntimeSelection select_desktop_xr_runtime(
+    bool openxr_available,
+    bool openvr_available,
+    bool allow_legacy_openvr_fallback) noexcept;
+
 [[nodiscard]] bool platform_deletes_recorded_files_on_clear(PlatformFamily family) noexcept;
 [[nodiscard]] bool platform_publishes_exported_images(PlatformFamily family) noexcept;
 [[nodiscard]] bool platform_flushes_persistent_storage(PlatformFamily family) noexcept;

src/platform_windows/windows_platform_services.cpp

@@ -209,6 +209,15 @@ void ensure_directory(const std::string& path)
         CreateDirectoryA(path.c_str(), NULL);
 }
 
+[[nodiscard]] pp::platform::XrRuntimeSelection select_windows_xr_runtime() noexcept
+{
+    // DEBT-0061: OpenXR is the target backend; Windows only exposes the retained OpenVR bridge today.
+    return pp::platform::select_desktop_xr_runtime(
+        false,
+        true,
+        true);
+}
+
 std::string build_supported_files_filter(const std::vector<std::string>& types)
 {
     std::string filter = "Supported Files (";
@@ -442,12 +451,33 @@ public:
 
     [[nodiscard]] bool start_vr_mode() override
     {
-        return win32_vr_start();
+        const auto runtime = select_windows_xr_runtime();
+        if (runtime.backend == pp::platform::XrRuntimeBackend::openvr)
+        {
+            active_xr_runtime_backend_ = pp::platform::XrRuntimeBackend::none;
+            if (win32_vr_start())
+                active_xr_runtime_backend_ = runtime.backend;
+            return active_xr_runtime_backend_ == runtime.backend;
+        }
+
+        if (runtime.backend == pp::platform::XrRuntimeBackend::openxr)
+            LOG("OpenXR runtime selected but the Windows OpenXR backend is not wired yet");
+
+        return false;
     }
 
     void stop_vr_mode() override
     {
-        win32_vr_stop();
+        auto runtime = active_xr_runtime_backend_;
+        if (runtime == pp::platform::XrRuntimeBackend::none)
+            runtime = select_windows_xr_runtime().backend;
+
+        if (runtime == pp::platform::XrRuntimeBackend::openvr)
+            win32_vr_stop();
+        else if (runtime == pp::platform::XrRuntimeBackend::openxr)
+            LOG("OpenXR runtime selected but the Windows OpenXR stop path is not wired yet");
+
+        active_xr_runtime_backend_ = pp::platform::XrRuntimeBackend::none;
     }
 
     void pick_image(pp::platform::PickedPathCallback callback) override
@@ -572,6 +602,9 @@ public:
         (void)suggested_name;
         callback(std::string(path), false);
     }
+
+private:
+    pp::platform::XrRuntimeBackend active_xr_runtime_backend_ = pp::platform::XrRuntimeBackend::none;
 };
 
 }