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;