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OBJ import: ensure we only skip identical vertices (#1444)

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just hashing will give false positives, especially on Linux where
std::hash<int> is identity.

Fixes #1405
This commit is contained in:
Dennis Brakhane
2026-01-02 14:31:24 +01:00
committed by GitHub
parent bf2f369bf0
commit b962a7221e
1 changed files with 30 additions and 11 deletions
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Editor/ModelImporter_OBJ.cpp
+30 -11
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@@ -75,6 +75,31 @@ private:
// Transform the data from OBJ space to engine-space:
static const bool transform_to_LH = true;
struct index_and_mat
{
tinyobj::index_t index;
int materialIndex;
constexpr bool operator==(const index_and_mat& other) const
{
return std::tuple(index.normal_index, index.texcoord_index, index.vertex_index, materialIndex)
== std::tuple(other.index.normal_index, other.index.texcoord_index, other.index.vertex_index, other.materialIndex);
}
};
template<>
struct std::hash<index_and_mat>
{
constexpr std::size_t operator()(const index_and_mat& o) const noexcept
{
size_t vertexHash = 0;
wi::helper::hash_combine(vertexHash, o.index.vertex_index);
wi::helper::hash_combine(vertexHash, o.index.normal_index);
wi::helper::hash_combine(vertexHash, o.index.texcoord_index);
wi::helper::hash_combine(vertexHash, o.materialIndex);
return vertexHash;
}
};
void ImportModel_OBJ(const std::string& fileName, Scene& scene)
{
std::string directory = wi::helper::GetDirectoryFromPath(fileName);
@@ -176,7 +201,7 @@ void ImportModel_OBJ(const std::string& fileName, Scene& scene)
object.meshID = meshEntity;
wi::unordered_map<int, int> registered_materialIndices = {};
wi::unordered_map<size_t, uint32_t> uniqueVertices = {};
wi::unordered_map<index_and_mat, uint32_t> uniqueVertices = {};
for (size_t i = 0; i < shape.mesh.indices.size(); i += 3)
{
@@ -236,21 +261,15 @@ void ImportModel_OBJ(const std::string& fileName, Scene& scene)
nor.z *= -1;
}
// eliminate duplicate vertices by means of hashing:
size_t vertexHash = 0;
wi::helper::hash_combine(vertexHash, index.vertex_index);
wi::helper::hash_combine(vertexHash, index.normal_index);
wi::helper::hash_combine(vertexHash, index.texcoord_index);
wi::helper::hash_combine(vertexHash, materialIndex);
if (uniqueVertices.count(vertexHash) == 0)
const index_and_mat im = {index, materialIndex};
if (uniqueVertices.count(im) == 0)
{
uniqueVertices[vertexHash] = (uint32_t)mesh.vertex_positions.size();
uniqueVertices[im] = (uint32_t)mesh.vertex_positions.size();
mesh.vertex_positions.push_back(pos);
mesh.vertex_normals.push_back(nor);
mesh.vertex_uvset_0.push_back(tex);
}
mesh.indices.push_back(uniqueVertices[vertexHash]);
mesh.indices.push_back(uniqueVertices[im]);
mesh.subsets.back().indexCount++;
}
}