Add tests for credit filtering.

There's no good reason this was so complicated before.

CHANGES.md

@@ -8,13 +8,13 @@
 - The constructor parameters for `RasterOverlayTileProvider` and `QuadtreeRasterOverlayTileProvider` have changed.
 - The `getCredit` method has been removed from `RasterOverlayCreditProvider`. Use `getCredits` instead.
 - Removed unused property `RasterOverlayOptions::subTileCacheBytes`.
-- The `CreditSystem` would previously treat credits with identical text as the same credit, even if they came from different sources. Now, credits from different `CreditSource` instances are treated as different credits.
 
 ##### Additions :tada:
 
 - Added the concept of a `CreditSource`. Every `Credit` in a `CreditSystem` has a source, and these can be mapped back to `Tileset` and `RasterOverlayTileProvider` (via their `getCreditSource` methods) in order to determine which dataset created which credits.
 - Added `TilesetViewGroup::isCreditReferenced`, which can be used to determine if a particular view group references a particular `Credit`.
 - Added `CreditReferencer::isCreditReferenced`, which can be used to determine if the referencer is currently referencing a particular `Credit`.
+- `CreditSystem::getSnapshot` now takes an optional parameter specifying if and how to filter `Credits` with identical HTML strings.
 
 ### v0.54.0 - 2025-11-17
 

Cesium3DTilesSelection/test/TestCreditSystem.cpp

@@ -326,4 +326,158 @@ TEST_CASE("Test CreditSystem with CreditSources") {
     CHECK(snapshot.currentCredits[0] == credit1);
     CHECK(snapshot.removedCredits.empty());
   }
+
+  SUBCASE("getSnapshot") {
+    SUBCASE("None filtering mode") {
+      SUBCASE("includes all Credits from all sources") {
+        CreditSource sourceC(creditSystem);
+        Credit credit0 = creditSystem.createCredit(sourceA, html0);
+        Credit credit1 = creditSystem.createCredit(sourceB, html0);
+        Credit credit2 = creditSystem.createCredit(sourceC, html0);
+
+        creditSystem.addCreditReference(credit0);
+        creditSystem.addCreditReference(credit1);
+        creditSystem.addCreditReference(credit2);
+
+        const CreditsSnapshot& snapshot =
+            creditSystem.getSnapshot(CreditFilteringMode::None);
+
+        REQUIRE(snapshot.currentCredits.size() == 3);
+        CHECK(snapshot.currentCredits[0] == credit0);
+        CHECK(snapshot.currentCredits[1] == credit1);
+        CHECK(snapshot.currentCredits[2] == credit2);
+        CHECK(snapshot.removedCredits.empty());
+      }
+    }
+
+    SUBCASE("UniqueHtmlAndShowOnScreen filtering mode") {
+      SUBCASE(
+          "filters out credits with identical HTML and showOnScreen values") {
+        CreditSource sourceC(creditSystem);
+        Credit credit0 = creditSystem.createCredit(sourceA, html0, true);
+        Credit credit1 = creditSystem.createCredit(sourceB, html0, true);
+        Credit credit2 = creditSystem.createCredit(sourceC, html0, false);
+
+        creditSystem.addCreditReference(credit0);
+        creditSystem.addCreditReference(credit1);
+        creditSystem.addCreditReference(credit2);
+
+        const CreditsSnapshot& snapshot = creditSystem.getSnapshot(
+            CreditFilteringMode::UniqueHtmlAndShowOnScreen);
+
+        REQUIRE(snapshot.currentCredits.size() == 2);
+        CHECK(snapshot.currentCredits[0] == credit0);
+        CHECK(snapshot.currentCredits[1] == credit2);
+        CHECK(snapshot.removedCredits.empty());
+      }
+
+      SUBCASE("reference count is the sum of collapsed credits") {
+        CreditSource sourceC(creditSystem);
+        Credit credit0 = creditSystem.createCredit(sourceA, html0, false);
+        Credit credit1 = creditSystem.createCredit(sourceB, html0, true);
+        Credit credit2 = creditSystem.createCredit(sourceC, html0, true);
+
+        creditSystem.addCreditReference(credit0);
+        creditSystem.addCreditReference(credit0);
+        creditSystem.addCreditReference(credit1);
+        creditSystem.addCreditReference(credit2);
+        creditSystem.addCreditReference(credit2);
+
+        const CreditsSnapshot& snapshot = creditSystem.getSnapshot(
+            CreditFilteringMode::UniqueHtmlAndShowOnScreen);
+
+        // credit0 has a reference count of 2. credit1 and credit2 are collapsed
+        // into one credit with a reference count of 3 and represented by
+        // credit1. So credit1 should be shown before credit0.
+        REQUIRE(snapshot.currentCredits.size() == 2);
+        CHECK(snapshot.currentCredits[0] == credit1);
+        CHECK(snapshot.currentCredits[1] == credit0);
+        CHECK(snapshot.removedCredits.empty());
+      }
+    }
+
+    SUBCASE("UniqueHtml filtering mode") {
+      SUBCASE(
+          "filters out credits with identical HTML from different sources") {
+        CreditSource sourceC(creditSystem);
+        Credit credit0 = creditSystem.createCredit(sourceA, html0);
+        Credit credit1 = creditSystem.createCredit(sourceB, html0);
+        Credit credit2 = creditSystem.createCredit(sourceC, html0);
+
+        creditSystem.addCreditReference(credit0);
+        creditSystem.addCreditReference(credit1);
+        creditSystem.addCreditReference(credit2);
+
+        const CreditsSnapshot& snapshot =
+            creditSystem.getSnapshot(CreditFilteringMode::UniqueHtml);
+
+        REQUIRE(snapshot.currentCredits.size() == 1);
+        CHECK(snapshot.currentCredits[0] == credit0);
+        CHECK(snapshot.removedCredits.empty());
+      }
+
+      SUBCASE("includes the Credit with showOnScreen=true if one exists.") {
+        CreditSource sourceC(creditSystem);
+        Credit credit0 = creditSystem.createCredit(sourceA, html0, false);
+        Credit credit1 = creditSystem.createCredit(sourceB, html0, true);
+        Credit credit2 = creditSystem.createCredit(sourceC, html0, false);
+
+        creditSystem.addCreditReference(credit0);
+        creditSystem.addCreditReference(credit1);
+        creditSystem.addCreditReference(credit2);
+
+        const CreditsSnapshot& snapshot =
+            creditSystem.getSnapshot(CreditFilteringMode::UniqueHtml);
+
+        REQUIRE(snapshot.currentCredits.size() == 1);
+        CHECK(snapshot.currentCredits[0] == credit1);
+        CHECK(snapshot.removedCredits.empty());
+      }
+
+      SUBCASE("includes the first of multiple Credits with showOnScreen=true") {
+        CreditSource sourceC(creditSystem);
+        Credit credit0 = creditSystem.createCredit(sourceA, html0, true);
+        Credit credit1 = creditSystem.createCredit(sourceB, html0, true);
+        Credit credit2 = creditSystem.createCredit(sourceC, html0, false);
+
+        creditSystem.addCreditReference(credit0);
+        creditSystem.addCreditReference(credit1);
+        creditSystem.addCreditReference(credit2);
+
+        const CreditsSnapshot& snapshot =
+            creditSystem.getSnapshot(CreditFilteringMode::UniqueHtml);
+
+        REQUIRE(snapshot.currentCredits.size() == 1);
+        CHECK(snapshot.currentCredits[0] == credit0);
+        CHECK(snapshot.removedCredits.empty());
+      }
+
+      SUBCASE("reference count is the sum of collapsed credits") {
+        CreditSource sourceC(creditSystem);
+        Credit credit0 = creditSystem.createCredit(sourceA, html0);
+        Credit credit1 = creditSystem.createCredit(sourceB, html1);
+        Credit credit2 = creditSystem.createCredit(sourceC, html1);
+
+        creditSystem.addCreditReference(credit0);
+        creditSystem.addCreditReference(credit0);
+        creditSystem.addCreditReference(credit1);
+        creditSystem.addCreditReference(credit2);
+        creditSystem.addCreditReference(credit2);
+
+        const CreditsSnapshot& snapshot =
+            creditSystem.getSnapshot(CreditFilteringMode::UniqueHtml);
+
+        // credit0 has a reference count of 2. credit1 and credit2 are collapsed
+        // into one credit with a reference count of 3 and represented by
+        // credit1. So credit1 should be shown before credit0.
+        REQUIRE(snapshot.currentCredits.size() == 2);
+        CHECK(snapshot.currentCredits[0] == credit1);
+        CHECK(snapshot.currentCredits[1] == credit0);
+        CHECK(snapshot.removedCredits.empty());
+      }
+    }
+  }
+
+  // Refeference count for sorting is the sum of collapsed credit reference
+  // counts.
 }

CesiumUtility/include/CesiumUtility/CreditSystem.h

@@ -3,6 +3,7 @@
 #include <CesiumUtility/Library.h>
 
 #include <cstdint>
+#include <limits>
 #include <memory>
 #include <string>
 #include <unordered_map>
@@ -13,6 +14,43 @@ namespace CesiumUtility {
 
 class CreditSystem;
 
+/**
+ * @brief Specifies how credit system snapshots should handle multiple
+ * credits with the same HTML string.
+ */
+enum class CreditFilteringMode : uint8_t {
+  /**
+   * @brief No filtering is performed. Each unique @ref Credit is reported.
+   */
+  None = 0,
+
+  /**
+   * @brief Credits are filtered so that each reported credit has a combination
+   * of HTML string and @ref CreditSystem::shouldBeShownOnScreen value that is
+   * unique from all the other reported credits.
+   *
+   * If multiple credits have the same HTML string but different
+   * @ref CreditSystem::shouldBeShownOnScreen values, they will be reported as
+   * separate credits.
+   *
+   * It is unspecified which of the multiple credits with the same properties
+   * will be reported.
+   */
+  UniqueHtmlAndShowOnScreen = 1,
+
+  /**
+   * @brief Credits with identical HTML strings are reported as one Credit even
+   * if they have a different @ref CreditSource or @ref
+   * CreditSystem::shouldBeShownOnScreen value.
+   *
+   * It is unspecified which of the multiple credits with the same source will
+   * be reported. However, it is guaranteed that if any of the multiple credits
+   * has @ref CreditSystem::shouldBeShownOnScreen set to `true`, the reported
+   * credit will also have it set to `true`.
+   */
+  UniqueHtml = 2
+};
+
 /**
  * @brief Represents an HTML string that should be shown on screen to attribute
  * third parties for used data, imagery, etc. Acts as a handle into a
@@ -116,8 +154,15 @@ struct CreditsSnapshot {
  */
 class CESIUMUTILITY_API CreditSystem final {
 public:
+  /**
+   * @brief Constructs a new instance.
+   */
+  CreditSystem() noexcept = default;
   ~CreditSystem() noexcept;
 
+  CreditSystem(const CreditSystem&) = delete;
+  CreditSystem& operator=(const CreditSystem&) = delete;
+
   /**
    * @brief Inserts a credit string.
    *
@@ -227,8 +272,13 @@ public:
    * The snapshot will include a sorted list of credits that are currently
    * active, as well as a list of credits that have been removed since the last
    * snapshot.
+   *
+   * @param filteringMode Specifies how multiple credits with the same HTML
+   * string should be reported in the snapshot.
    */
-  const CreditsSnapshot& getSnapshot() noexcept;
+  const CreditsSnapshot& getSnapshot(
+      CreditFilteringMode filteringMode =
+          CreditFilteringMode::UniqueHtml) noexcept;
 
   /**
    * @brief Gets the default credit source used when no other source is
@@ -240,6 +290,17 @@ public:
   const CreditSource& getDefaultCreditSource() const noexcept;
 
 private:
+  struct CreditRecord {
+    std::string html{};
+    bool showOnScreen{false};
+    int32_t referenceCount{0};
+    bool shownLastSnapshot{0};
+    uint32_t generation{0};
+    const CreditSource* pSource{nullptr};
+    uint32_t previousCreditWithSameHtml{INVALID_CREDIT_INDEX};
+    uint32_t nextCreditWithSameHtml{INVALID_CREDIT_INDEX};
+  };
+
   void addBulkReferences(
       const std::vector<int32_t>& references,
       const std::vector<uint32_t>& generations) noexcept;
@@ -250,22 +311,20 @@ private:
   void createCreditSource(CreditSource& creditSource) noexcept;
   void destroyCreditSource(CreditSource& creditSource) noexcept;
 
+  uint32_t filterCreditForSnapshot(
+      CreditFilteringMode filteringMode,
+      const CreditRecord& record) noexcept;
+
   const std::string INVALID_CREDIT_MESSAGE =
       "Error: Invalid Credit, cannot get HTML string.";
 
-  struct CreditRecord {
-    std::string html{};
-    bool showOnScreen{false};
-    int32_t referenceCount{0};
-    bool shownLastSnapshot{0};
-    uint32_t generation{0};
-    const CreditSource* pSource{nullptr};
-  };
+  static const uint32_t INVALID_CREDIT_INDEX{
+      std::numeric_limits<uint32_t>::max()};
 
   std::vector<CreditSource*> _creditSources;
   std::vector<CreditRecord> _credits;
-  std::vector<Credit> _creditsToNoLongerShowThisSnapshot;
   CreditsSnapshot _snapshot;
+  std::vector<int32_t> _referenceCountScratch;
 
   // Each entry in this vector is an index into _credits that is unused and can
   // be reused for a new credit.

CesiumUtility/src/CreditSystem.cpp

@@ -61,12 +61,18 @@ Credit CreditSystem::createCredit(
     std::string&& html,
     bool showOnScreen) {
   // If this credit already exists, return a Credit handle to it
+  uint32_t lastCreditWithSameHtml = INVALID_CREDIT_INDEX;
   for (size_t id = 0; id < this->_credits.size(); ++id) {
     CreditRecord& record = this->_credits[id];
-    if (record.pSource == &source && record.html == html) {
-      // Override the existing credit's showOnScreen value.
-      record.showOnScreen = showOnScreen;
-      return Credit(uint32_t(id), record.generation);
+    if (record.html == html) {
+      if (record.pSource == &source) {
+        // Override the existing credit's showOnScreen value.
+        record.showOnScreen = showOnScreen;
+        return Credit(uint32_t(id), record.generation);
+      } else if (record.pSource != nullptr) {
+        // Same HTML, but different source.
+        lastCreditWithSameHtml = uint32_t(id);
+      }
     }
   }
 
@@ -90,6 +96,14 @@ Credit CreditSystem::createCredit(
   // slot was destroyed.
   record.pSource = &source;
 
+  if (lastCreditWithSameHtml != INVALID_CREDIT_INDEX) {
+    record.previousCreditWithSameHtml = lastCreditWithSameHtml;
+    record.nextCreditWithSameHtml = INVALID_CREDIT_INDEX;
+    CreditRecord& lastRecord = this->_credits[size_t(lastCreditWithSameHtml)];
+    CESIUM_ASSERT(lastRecord.nextCreditWithSameHtml == INVALID_CREDIT_INDEX);
+    lastRecord.nextCreditWithSameHtml = uint32_t(creditIndex);
+  }
+
   return Credit(uint32_t(creditIndex), record.generation);
 }
 
@@ -147,19 +161,6 @@ bool CreditSystem::addCreditReference(Credit credit) {
 
   ++record.referenceCount;
 
-  // If this is the first reference to this credit, and it was shown last frame,
-  // make sure this credit doesn't exist in _creditsToNoLongerShowThisSnapshot.
-  if (record.shownLastSnapshot && record.referenceCount == 1) {
-    this->_creditsToNoLongerShowThisSnapshot.erase(
-        std::remove_if(
-            this->_creditsToNoLongerShowThisSnapshot.begin(),
-            this->_creditsToNoLongerShowThisSnapshot.end(),
-            [id = credit._id](const Credit& candidate) {
-              return candidate._id == id;
-            }),
-        this->_creditsToNoLongerShowThisSnapshot.end());
-  }
-
   return true;
 }
 
@@ -174,18 +175,18 @@ bool CreditSystem::removeCreditReference(Credit credit) {
   CESIUM_ASSERT(record.referenceCount > 0);
   --record.referenceCount;
 
-  // If this was the last reference to this credit, and it was shown last frame,
-  // add this credit to _creditsToNoLongerShowThisSnapshot.
-  if (record.shownLastSnapshot && record.referenceCount == 0) {
-    this->_creditsToNoLongerShowThisSnapshot.emplace_back(credit);
-  }
-
   return true;
 }
 
-const CreditsSnapshot& CreditSystem::getSnapshot() noexcept {
+const CreditsSnapshot&
+CreditSystem::getSnapshot(CreditFilteringMode filteringMode) noexcept {
   std::vector<Credit>& currentCredits = this->_snapshot.currentCredits;
+  std::vector<Credit>& removedCredits = this->_snapshot.removedCredits;
   currentCredits.clear();
+  removedCredits.clear();
+
+  std::vector<int32_t>& effectiveReferenceCounts = this->_referenceCountScratch;
+  effectiveReferenceCounts.assign(this->_credits.size(), 0);
 
   for (size_t i = 0; i < this->_credits.size(); ++i) {
     CreditRecord& record = this->_credits[i];
@@ -194,23 +195,38 @@ const CreditsSnapshot& CreditSystem::getSnapshot() noexcept {
     // count of zero.
     if (record.referenceCount > 0) {
       CESIUM_ASSERT(record.pSource != nullptr);
-      currentCredits.emplace_back(Credit(uint32_t(i), record.generation));
-      record.shownLastSnapshot = true;
-    } else {
+
+      // This credit is active, but it may be filtered out in favor of another
+      // credit with the same HTML.
+      uint32_t filteredInFavorOf =
+          this->filterCreditForSnapshot(filteringMode, record);
+      if (filteredInFavorOf != INVALID_CREDIT_INDEX) {
+        // Credit filtered out in favor of another credit.
+        // That other credit inherits this credit's reference count.
+        effectiveReferenceCounts[filteredInFavorOf] += record.referenceCount;
+        if (record.shownLastSnapshot) {
+          removedCredits.emplace_back(Credit(uint32_t(i), record.generation));
+          record.shownLastSnapshot = false;
+        }
+      } else {
+        // This credit is not filtered.
+        currentCredits.emplace_back(Credit(uint32_t(i), record.generation));
+        effectiveReferenceCounts[i] += record.referenceCount;
+        record.shownLastSnapshot = true;
+      }
+    } else if (record.shownLastSnapshot) {
+      removedCredits.emplace_back(Credit(uint32_t(i), record.generation));
       record.shownLastSnapshot = false;
     }
   }
 
-  this->_creditsToNoLongerShowThisSnapshot.swap(this->_snapshot.removedCredits);
-  this->_creditsToNoLongerShowThisSnapshot.clear();
-
   // sort credits based on the number of occurrences
   std::sort(
       currentCredits.begin(),
       currentCredits.end(),
-      [this](const Credit& a, const Credit& b) {
-        int32_t aCounts = this->_credits[a._id].referenceCount;
-        int32_t bCounts = this->_credits[b._id].referenceCount;
+      [&](const Credit& a, const Credit& b) {
+        int32_t aCounts = effectiveReferenceCounts[a._id];
+        int32_t bCounts = effectiveReferenceCounts[b._id];
         if (aCounts == bCounts)
           return a._id < b._id;
         else
@@ -238,20 +254,6 @@ void CreditSystem::addBulkReferences(
     int32_t referencesToAdd = references[i];
 
     record.referenceCount += referencesToAdd;
-
-    // If this is the first reference to this credit, and it was shown last
-    // frame, make sure this credit doesn't exist in
-    // _creditsToNoLongerShowThisSnapshot.
-    if (record.shownLastSnapshot && record.referenceCount == referencesToAdd) {
-      this->_creditsToNoLongerShowThisSnapshot.erase(
-          std::remove_if(
-              this->_creditsToNoLongerShowThisSnapshot.begin(),
-              this->_creditsToNoLongerShowThisSnapshot.end(),
-              [i = uint32_t(i)](const Credit& candidate) {
-                return candidate._id == i;
-              }),
-          this->_creditsToNoLongerShowThisSnapshot.end());
-    }
   }
 }
 
@@ -270,13 +272,6 @@ void CreditSystem::releaseBulkReferences(
 
     CESIUM_ASSERT(record.referenceCount >= referencesToRemove);
     record.referenceCount -= referencesToRemove;
-
-    // If this was the last reference to this credit, and it was shown last
-    // frame, add this credit to _creditsToNoLongerShowThisSnapshot.
-    if (record.shownLastSnapshot && record.referenceCount == 0) {
-      this->_creditsToNoLongerShowThisSnapshot.emplace_back(
-          Credit(uint32_t(i), record.generation));
-    }
   }
 }
 
@@ -291,17 +286,24 @@ void CreditSystem::destroyCreditSource(CreditSource& creditSource) noexcept {
       ++record.generation;
       this->_unusedCreditRecords.emplace_back(&record - this->_credits.data());
 
-      if (record.referenceCount > 0) {
-        record.referenceCount = 0;
-      } else {
-        this->_creditsToNoLongerShowThisSnapshot.erase(
-            std::remove_if(
-                this->_creditsToNoLongerShowThisSnapshot.begin(),
-                this->_creditsToNoLongerShowThisSnapshot.end(),
-                [id = uint32_t(&record - this->_credits.data())](
-                    const Credit& candidate) { return candidate._id == id; }),
-            this->_creditsToNoLongerShowThisSnapshot.end());
+      // Delete this record from the linked list of credits with the same HTML.
+      if (record.nextCreditWithSameHtml != INVALID_CREDIT_INDEX) {
+        CreditRecord& nextRecord =
+            this->_credits[record.nextCreditWithSameHtml];
+        nextRecord.previousCreditWithSameHtml =
+            record.previousCreditWithSameHtml;
+        record.nextCreditWithSameHtml = INVALID_CREDIT_INDEX;
       }
+
+      if (record.previousCreditWithSameHtml != INVALID_CREDIT_INDEX) {
+        CreditRecord& previousRecord =
+            this->_credits[record.previousCreditWithSameHtml];
+        previousRecord.nextCreditWithSameHtml = record.nextCreditWithSameHtml;
+        record.previousCreditWithSameHtml = INVALID_CREDIT_INDEX;
+      }
+
+      record.referenceCount = 0;
+      record.shownLastSnapshot = false;
     }
   }
 
@@ -313,4 +315,72 @@ void CreditSystem::destroyCreditSource(CreditSource& creditSource) noexcept {
       this->_creditSources.end());
 }
 
+uint32_t CreditSystem::filterCreditForSnapshot(
+    CreditFilteringMode filteringMode,
+    const CreditRecord& record) noexcept {
+  if (filteringMode == CreditFilteringMode::None) {
+    return CreditSystem::INVALID_CREDIT_INDEX;
+  } else if (filteringMode == CreditFilteringMode::UniqueHtmlAndShowOnScreen) {
+    uint32_t currentCreditIndex = record.previousCreditWithSameHtml;
+
+    while (currentCreditIndex != INVALID_CREDIT_INDEX) {
+      const CreditRecord& otherRecord =
+          this->_credits[size_t(currentCreditIndex)];
+
+      // If the other credit has the same showOnScreen value, filter this one
+      // out in favor of it.
+      if (otherRecord.showOnScreen == record.showOnScreen) {
+        return currentCreditIndex;
+      }
+
+      currentCreditIndex = otherRecord.previousCreditWithSameHtml;
+    }
+
+    return CreditSystem::INVALID_CREDIT_INDEX;
+  } else {
+    CESIUM_ASSERT(filteringMode == CreditFilteringMode::UniqueHtml);
+
+    // In this filtering mode, we need to find the first credit in the linked
+    // list with showOnScreen=true. Or if they're all showOnScreen=false, return
+    // the first one. Unlike `UniqueHtmlAndShowOnScreen`, the Credit we want may
+    // occur after the current one.
+
+    // Walk backwards to find the first credit in the linked list.
+    uint32_t previousCreditIndex = uint32_t(&record - this->_credits.data());
+    uint32_t firstCreditIndex;
+    do {
+      firstCreditIndex = previousCreditIndex;
+      const CreditRecord& otherRecord =
+          this->_credits[size_t(firstCreditIndex)];
+      previousCreditIndex = otherRecord.previousCreditWithSameHtml;
+    } while (previousCreditIndex != INVALID_CREDIT_INDEX);
+
+    // Walk forward from the first credit to find one with showOnScreen=true (if
+    // any).
+    uint32_t currentCreditIndex = firstCreditIndex;
+    while (currentCreditIndex != INVALID_CREDIT_INDEX) {
+      const CreditRecord& otherRecord =
+          this->_credits[size_t(currentCreditIndex)];
+
+      if (otherRecord.showOnScreen) {
+        // Found the first credit with showOnScreen=true. Filter this credit out
+        // in favor of it. Unless the currentCreditIndex points to the same
+        // credit we started with!
+        return currentCreditIndex == uint32_t(&record - this->_credits.data())
+                   ? CreditSystem::INVALID_CREDIT_INDEX
+                   : currentCreditIndex;
+      }
+
+      currentCreditIndex = otherRecord.nextCreditWithSameHtml;
+    }
+
+    // Reached the end of the linked list without finding any credit with
+    // showOnScreen=true. So return the first credit in the list. Unless the
+    // firstCreditIndex points to the same credit we started with!
+    return firstCreditIndex == uint32_t(&record - this->_credits.data())
+               ? CreditSystem::INVALID_CREDIT_INDEX
+               : firstCreditIndex;
+  }
+}
+
 } // namespace CesiumUtility