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[core] coveredByChildren is false if at least one child is uncovered #12371

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Jul 24, 2018
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[core] coveredByChildren is false if at least one child is uncovered #12371

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16 changes: 12 additions & 4 deletions src/mbgl/algorithm/covered_by_children.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -8,15 +8,23 @@ namespace algorithm {
template <typename Iterator>
bool coveredByChildren(const UnwrappedTileID& id, Iterator it, const Iterator& end) {
for (const auto& child : id.children()) {
it = std::lower_bound(it, end, child, [](auto& a, auto& b) { return std::get<0>(a) < b; });
it = std::lower_bound(it, end, child, [](const auto& a, const auto& b) { return std::get<0>(a) < b; });

// Child is not present, neither its grandchildren.
if (it == end) {
return false;
} else if (std::get<0>(*it) != child) {
return coveredByChildren(child, it, end);
}

// Child is not present, but its grandchildren are.
if (std::get<0>(*it) != child) {
// This child is not covered by its grandchildren.
if (!coveredByChildren(child, it, end)) {
return false;
}
}
}

// We looked at all four immediate children and verified that they're covered.
// We looked at all four children (recursively) and verified that they're covered.
return true;
}

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44 changes: 43 additions & 1 deletion test/algorithm/covered_by_children.test.cpp
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Expand Up @@ -8,6 +8,48 @@ using namespace mbgl;

using List = std::map<UnwrappedTileID, bool>;

TEST(CoveredByChildren, GrandChildren) {
const List list {
{ UnwrappedTileID{ 0, 0, 0 }, true },
// These grandchildren covers 1/0/0, but 1/0/0 only covers a quarter of
// 0/0/0.
{ UnwrappedTileID{ 2, 0, 0 }, true },
{ UnwrappedTileID{ 2, 0, 1 }, true },
{ UnwrappedTileID{ 2, 1, 0 }, true },
{ UnwrappedTileID{ 2, 1, 1 }, true },
};
EXPECT_FALSE(algorithm::coveredByChildren(UnwrappedTileID{ 0, 0, 0 }, list));

const List list2 {
{ UnwrappedTileID{ 0, 0, 0 }, true },

// Children of 1/0/0
{ UnwrappedTileID{ 2, 0, 0 }, true },
{ UnwrappedTileID{ 2, 0, 1 }, true },
{ UnwrappedTileID{ 2, 1, 0 }, true },
{ UnwrappedTileID{ 2, 1, 1 }, true },

// Children of 1/0/1
{ UnwrappedTileID{ 2, 0, 2 }, true },
{ UnwrappedTileID{ 2, 0, 3 }, true },
{ UnwrappedTileID{ 2, 1, 2 }, true },
{ UnwrappedTileID{ 2, 1, 3 }, true },

// Children of 1/1/0
{ UnwrappedTileID{ 2, 2, 0 }, true },
{ UnwrappedTileID{ 2, 2, 1 }, true },
{ UnwrappedTileID{ 2, 3, 0 }, true },
{ UnwrappedTileID{ 2, 3, 1 }, true },

// Children of 1/0/1
{ UnwrappedTileID{ 2, 2, 2 }, true },
{ UnwrappedTileID{ 2, 2, 3 }, true },
{ UnwrappedTileID{ 2, 3, 2 }, true },
{ UnwrappedTileID{ 2, 3, 3 }, true },
};
EXPECT_TRUE(algorithm::coveredByChildren(UnwrappedTileID{ 0, 0, 0 }, list2));
}

TEST(CoveredByChildren, NotCovered) {
const List list1;
EXPECT_FALSE(algorithm::coveredByChildren(UnwrappedTileID{ 0, 0, 0 }, list1));
Expand All @@ -24,7 +66,7 @@ TEST(CoveredByChildren, NotCovered) {

const List list3{
{ UnwrappedTileID{ 0, 0, 0 }, true },
// all four child tiles, with with a different wrap index
// all four child tiles, with a different wrap index
{ UnwrappedTileID{ 1, { 1, 0, 0 } }, true },
{ UnwrappedTileID{ 1, { 1, 0, 1 } }, true },
{ UnwrappedTileID{ 1, { 1, 1, 0 } }, true },
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