Fix behaviour of shadow interpolation with mismatched list lengths

third_party/WebKit/Source/core/animation/ListInterpolationFunctions.cpp

Index: third_party/WebKit/Source/core/animation/ListInterpolationFunctions.cpp
diff --git a/third_party/WebKit/Source/core/animation/ListInterpolationFunctions.cpp b/third_party/WebKit/Source/core/animation/ListInterpolationFunctions.cpp
index 82b26f7cec11992684c1e2908b0a758aa0b42ac0..6f39102e39f4de4f5ac855dcb6028d25c720bfb3 100644
--- a/third_party/WebKit/Source/core/animation/ListInterpolationFunctions.cpp
+++ b/third_party/WebKit/Source/core/animation/ListInterpolationFunctions.cpp
@@ -48,12 +48,29 @@ bool ListInterpolationFunctions::EqualValues(
   return true;
 }
 
+static size_t MatchLengths(size_t start_length,
+                           size_t end_length,
+                           ListInterpolationFunctions::LengthMatchingStrategy
+                               length_matching_strategy) {
+  if (length_matching_strategy ==
+      ListInterpolationFunctions::LengthMatchingStrategy::
+          kLowestCommonMultiple) {
+    return lowestCommonMultiple(start_length, end_length);
+  }
+  DCHECK_EQ(length_matching_strategy,
+            ListInterpolationFunctions::LengthMatchingStrategy::kPadToLargest);
+  return std::max(start_length, end_length);
+}
+
 PairwiseInterpolationValue ListInterpolationFunctions::MaybeMergeSingles(
     InterpolationValue&& start,
     InterpolationValue&& end,
+    LengthMatchingStrategy length_matching_strategy,
     MergeSingleItemConversionsCallback merge_single_item_conversions) {
-  size_t start_length = ToInterpolableList(*start.interpolable_value).length();
-  size_t end_length = ToInterpolableList(*end.interpolable_value).length();
+  const size_t start_length =
+      ToInterpolableList(*start.interpolable_value).length();
+  const size_t end_length =
+      ToInterpolableList(*end.interpolable_value).length();
 
   if (start_length == 0 && end_length == 0) {
     return PairwiseInterpolationValue(std::move(start.interpolable_value),
@@ -77,7 +94,8 @@ PairwiseInterpolationValue ListInterpolationFunctions::MaybeMergeSingles(
                                       std::move(start.non_interpolable_value));
   }
 
-  size_t final_length = lowestCommonMultiple(start_length, end_length);
+  const size_t final_length =
+      MatchLengths(start_length, end_length, length_matching_strategy);
   std::unique_ptr<InterpolableList> result_start_interpolable_list =
       InterpolableList::Create(final_length);
   std::unique_ptr<InterpolableList> result_end_interpolable_list =
@@ -95,21 +113,43 @@ PairwiseInterpolationValue ListInterpolationFunctions::MaybeMergeSingles(
       ToNonInterpolableList(*end.non_interpolable_value);
 
   for (size_t i = 0; i < final_length; i++) {
-    InterpolationValue start(
-        start_interpolable_list.Get(i % start_length)->Clone(),
-        start_non_interpolable_list.Get(i % start_length));
-    InterpolationValue end(end_interpolable_list.Get(i % end_length)->Clone(),
-                           end_non_interpolable_list.Get(i % end_length));
-    PairwiseInterpolationValue result =
-        merge_single_item_conversions(std::move(start), std::move(end));
-    if (!result)
-      return nullptr;
-    result_start_interpolable_list->Set(
-        i, std::move(result.start_interpolable_value));
-    result_end_interpolable_list->Set(i,
-                                      std::move(result.end_interpolable_value));
-    result_non_interpolable_values[i] =
-        std::move(result.non_interpolable_value);
+    PairwiseInterpolationValue result = nullptr;
+    if (length_matching_strategy ==
+            LengthMatchingStrategy::kLowestCommonMultiple ||
+        (i < start_length && i < end_length)) {
+      InterpolationValue start(
+          start_interpolable_list.Get(i % start_length)->Clone(),
+          start_non_interpolable_list.Get(i % start_length));
+      InterpolationValue end(end_interpolable_list.Get(i % end_length)->Clone(),
+                             end_non_interpolable_list.Get(i % end_length));
+      PairwiseInterpolationValue result =
+          merge_single_item_conversions(std::move(start), std::move(end));
+      if (!result)
+        return nullptr;
+      result_start_interpolable_list->Set(
+          i, std::move(result.start_interpolable_value));
+      result_end_interpolable_list->Set(
+          i, std::move(result.end_interpolable_value));
+      result_non_interpolable_values[i] =
+          std::move(result.non_interpolable_value);
+    } else {
+      DCHECK_EQ(length_matching_strategy,
+                LengthMatchingStrategy::kPadToLargest);
+      if (i < start_length) {
+        result_start_interpolable_list->Set(
+            i, start_interpolable_list.Get(i)->Clone());
+        result_end_interpolable_list->Set(
+            i, start_interpolable_list.Get(i)->CloneAndZero());
+        result_non_interpolable_values[i] = start_non_interpolable_list.Get(i);
+      } else {
+        DCHECK_LT(i, end_length);
+        result_start_interpolable_list->Set(
+            i, end_interpolable_list.Get(i)->CloneAndZero());
+        result_end_interpolable_list->Set(
+            i, end_interpolable_list.Get(i)->Clone());
+        result_non_interpolable_values[i] = end_non_interpolable_list.Get(i);
+      }
+    }
   }
 
   return PairwiseInterpolationValue(
@@ -144,16 +184,59 @@ static void RepeatToLength(InterpolationValue& value, size_t length) {
       NonInterpolableList::Create(std::move(new_non_interpolable_values));
 }
 
+// This helper function makes value the same length as length_value by
+// CloneAndZero-ing the additional items from length_value into value.
+static void PadToSameLength(InterpolationValue& value,
+                            const InterpolationValue& length_value) {
+  InterpolableList& interpolable_list =
+      ToInterpolableList(*value.interpolable_value);
+  NonInterpolableList& non_interpolable_list =
+      ToNonInterpolableList(*value.non_interpolable_value);
+  const size_t current_length = interpolable_list.length();
+  InterpolableList& target_interpolable_list =
+      ToInterpolableList(*length_value.interpolable_value);
+  NonInterpolableList& target_non_interpolable_list =
+      ToNonInterpolableList(*length_value.non_interpolable_value);
+  const size_t target_length = target_interpolable_list.length();
+  DCHECK_LT(current_length, target_length);
+  std::unique_ptr<InterpolableList> new_interpolable_list =
+      InterpolableList::Create(target_length);
+  Vector<RefPtr<NonInterpolableValue>> new_non_interpolable_values(
+      target_length);
+  size_t index = 0;
+  for (; index < current_length; index++) {
+    new_interpolable_list->Set(index,
+                               std::move(interpolable_list.GetMutable(index)));
+    new_non_interpolable_values[index] = non_interpolable_list.Get(index);
+  }
+  for (; index < target_length; index++) {
+    new_interpolable_list->Set(
+        index, target_interpolable_list.Get(index)->CloneAndZero());
+    new_non_interpolable_values[index] =
+        target_non_interpolable_list.Get(index);
+  }
+  value.interpolable_value = std::move(new_interpolable_list);
+  value.non_interpolable_value =
+      NonInterpolableList::Create(std::move(new_non_interpolable_values));
+}
+
 static bool NonInterpolableListsAreCompatible(
     const NonInterpolableList& a,
     const NonInterpolableList& b,
     size_t length,
+    ListInterpolationFunctions::LengthMatchingStrategy length_matching_strategy,
     ListInterpolationFunctions::NonInterpolableValuesAreCompatibleCallback
         non_interpolable_values_are_compatible) {
   for (size_t i = 0; i < length; i++) {
-    if (!non_interpolable_values_are_compatible(a.Get(i % a.length()),
-                                                b.Get(i % b.length())))
-      return false;
+    if (length_matching_strategy ==
+            ListInterpolationFunctions::LengthMatchingStrategy::
+                kLowestCommonMultiple ||
+        (i < a.length() && i < b.length())) {
+      if (!non_interpolable_values_are_compatible(a.Get(i % a.length()),
+                                                  b.Get(i % b.length()))) {
+        return false;
+      }
+    }
   }
   return true;
 }
@@ -163,10 +246,11 @@ void ListInterpolationFunctions::Composite(
     double underlying_fraction,
     const InterpolationType& type,
     const InterpolationValue& value,
+    LengthMatchingStrategy length_matching_strategy,
     NonInterpolableValuesAreCompatibleCallback
         non_interpolable_values_are_compatible,
     CompositeItemCallback composite_item) {
-  size_t underlying_length =
+  const size_t underlying_length =
       ToInterpolableList(*underlying_value_owner.Value().interpolable_value)
           .length();
   if (underlying_length == 0) {
@@ -177,7 +261,7 @@ void ListInterpolationFunctions::Composite(
 
   const InterpolableList& interpolable_list =
       ToInterpolableList(*value.interpolable_value);
-  size_t value_length = interpolable_list.length();
+  const size_t value_length = interpolable_list.length();
   if (value_length == 0) {
     DCHECK(!value.non_interpolable_value);
     underlying_value_owner.MutableValue().interpolable_value->Scale(
@@ -187,30 +271,55 @@ void ListInterpolationFunctions::Composite(
 
   const NonInterpolableList& non_interpolable_list =
       ToNonInterpolableList(*value.non_interpolable_value);
-  size_t new_length = lowestCommonMultiple(underlying_length, value_length);
+  const size_t final_length =
+      MatchLengths(underlying_length, value_length, length_matching_strategy);
   if (!NonInterpolableListsAreCompatible(
           ToNonInterpolableList(
               *underlying_value_owner.Value().non_interpolable_value),
-          non_interpolable_list, new_length,
+          non_interpolable_list, final_length, length_matching_strategy,
           non_interpolable_values_are_compatible)) {
     underlying_value_owner.Set(type, value);
     return;
   }
 
   InterpolationValue& underlying_value = underlying_value_owner.MutableValue();
-  if (underlying_length < new_length)
-    RepeatToLength(underlying_value, new_length);
-
-  InterpolableList& underlying_interpolable_list =
-      ToInterpolableList(*underlying_value.interpolable_value);
-  NonInterpolableList& underlying_non_interpolable_list =
-      ToNonInterpolableList(*underlying_value.non_interpolable_value);
-  for (size_t i = 0; i < new_length; i++) {
-    composite_item(underlying_interpolable_list.GetMutable(i),
-                   underlying_non_interpolable_list.GetMutable(i),
-                   underlying_fraction,
-                   *interpolable_list.Get(i % value_length),
-                   non_interpolable_list.Get(i % value_length));
+  if (length_matching_strategy ==
+      LengthMatchingStrategy::kLowestCommonMultiple) {
+    if (underlying_length < final_length) {
+      RepeatToLength(underlying_value, final_length);
+    }
+    InterpolableList& underlying_interpolable_list =
+        ToInterpolableList(*underlying_value.interpolable_value);
+    NonInterpolableList& underlying_non_interpolable_list =
+        ToNonInterpolableList(*underlying_value.non_interpolable_value);
+
+    for (size_t i = 0; i < final_length; i++) {
+      composite_item(underlying_interpolable_list.GetMutable(i),
+                     underlying_non_interpolable_list.GetMutable(i),
+                     underlying_fraction,
+                     *interpolable_list.Get(i % value_length),
+                     non_interpolable_list.Get(i % value_length));
+    }
+  } else {
+    DCHECK_EQ(length_matching_strategy, LengthMatchingStrategy::kPadToLargest);
+    if (underlying_length < final_length) {
+      DCHECK_EQ(value_length, final_length);
+      PadToSameLength(underlying_value, value);
+    }
+    InterpolableList& underlying_interpolable_list =
+        ToInterpolableList(*underlying_value.interpolable_value);
+    NonInterpolableList& underlying_non_interpolable_list =
+        ToNonInterpolableList(*underlying_value.non_interpolable_value);
+
+    for (size_t i = 0; i < value_length; i++) {
+      composite_item(underlying_interpolable_list.GetMutable(i),
+                     underlying_non_interpolable_list.GetMutable(i),
+                     underlying_fraction, *interpolable_list.Get(i),
+                     non_interpolable_list.Get(i));
+    }
+    for (size_t i = value_length; i < final_length; i++) {
+      underlying_interpolable_list.GetMutable(i)->Scale(underlying_fraction);
+    }
   }
 }