refactor: formalize scene viewport object-id picking

editor/src/Viewport/ViewportObjectIdPicker.h

@@ -9,6 +9,7 @@
 
 #include <array>
 #include <cstdint>
+#include <utility>
 
 namespace XCEngine {
 namespace Editor {
@@ -32,6 +33,21 @@ struct ViewportObjectIdReadbackRequest {
     uint32_t pixelY = 0;
 };
 
+enum class ViewportObjectIdPickStatus : uint8_t {
+    Unavailable = 0,
+    Success,
+    ReadbackFailed
+};
+
+struct ViewportObjectIdPickResult {
+    ViewportObjectIdPickStatus status = ViewportObjectIdPickStatus::Unavailable;
+    uint64_t entityId = 0;
+
+    bool HasResolvedSample() const {
+        return status == ViewportObjectIdPickStatus::Success;
+    }
+};
+
 inline bool CanPickViewportObjectId(const ViewportObjectIdPickContext& context) {
     return context.commandQueue != nullptr &&
         context.texture != nullptr &&
@@ -67,28 +83,40 @@ inline bool BuildViewportObjectIdReadbackRequest(
 }
 
 template <typename ReadPixelFn>
-bool TryPickViewportObjectIdEntity(
+ViewportObjectIdPickResult PickViewportObjectIdEntity(
     const ViewportObjectIdPickContext& context,
-    ReadPixelFn&& readPixel,
-    uint64_t& outEntityId) {
-    outEntityId = 0;
+    ReadPixelFn&& readPixel) {
+    ViewportObjectIdPickResult result = {};
 
     ViewportObjectIdReadbackRequest request = {};
     if (!BuildViewportObjectIdReadbackRequest(context, request)) {
-        return false;
+        return result;
     }
 
     std::array<uint8_t, 4> rgba = {};
     if (!readPixel(request, rgba)) {
-        return false;
+        result.status = ViewportObjectIdPickStatus::ReadbackFailed;
+        return result;
     }
 
-    outEntityId = static_cast<uint64_t>(Rendering::DecodeObjectIdFromColor(
+    result.status = ViewportObjectIdPickStatus::Success;
+    result.entityId = static_cast<uint64_t>(Rendering::DecodeObjectIdFromColor(
         rgba[0],
         rgba[1],
         rgba[2],
         rgba[3]));
-    return true;
+    return result;
+}
+
+template <typename ReadPixelFn>
+bool TryPickViewportObjectIdEntity(
+    const ViewportObjectIdPickContext& context,
+    ReadPixelFn&& readPixel,
+    uint64_t& outEntityId) {
+    const ViewportObjectIdPickResult result =
+        PickViewportObjectIdEntity(context, std::forward<ReadPixelFn>(readPixel));
+    outEntityId = result.entityId;
+    return result.HasResolvedSample();
 }
 
 } // namespace Editor