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Merged
zeux merged 4 commits into from
May 12, 2025
Merged

gltfpack: Deindex meshes with abnormally large vertex accessors #885

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b8f0095
extern: Support sparse accessors for cgltf_accessor_read_*
zeux May 11, 2025
4c3ee45
gltfpack: Fix calls to accessor_read_float
zeux May 11, 2025
4415305
gltfpack: Deindex meshes with abnormally large vertex accessors on th…
zeux May 11, 2025
e9b0029
gltfpack: Only enable sparse mode for non-empty indices
zeux May 12, 2025
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47 changes: 43 additions & 4 deletions extern/cgltf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -2352,11 +2352,46 @@ const cgltf_accessor* cgltf_find_accessor(const cgltf_primitive* prim, cgltf_att
return NULL;
}

static const uint8_t* cgltf_find_sparse_index(const cgltf_accessor* accessor, cgltf_size needle)
{
const cgltf_accessor_sparse* sparse = &accessor->sparse;
const uint8_t* index_data = cgltf_buffer_view_data(sparse->indices_buffer_view);
const uint8_t* value_data = cgltf_buffer_view_data(sparse->values_buffer_view);

if (index_data == NULL || value_data == NULL)
return NULL;

index_data += sparse->indices_byte_offset;
value_data += sparse->values_byte_offset;

cgltf_size index_stride = cgltf_component_size(sparse->indices_component_type);

cgltf_size offset = 0;
cgltf_size length = sparse->count;

while (length)
{
cgltf_size rem = length % 2;
length /= 2;

cgltf_size index = cgltf_component_read_index(index_data + (offset + length) * index_stride, sparse->indices_component_type);
offset += index < needle ? length + rem : 0;
}

if (offset == sparse->count)
return NULL;

cgltf_size index = offset < sparse->count ? cgltf_component_read_index(index_data + offset * index_stride, sparse->indices_component_type) : (cgltf_size)-1;
return index == needle ? value_data + offset * accessor->stride : NULL;
}

cgltf_bool cgltf_accessor_read_float(const cgltf_accessor* accessor, cgltf_size index, cgltf_float* out, cgltf_size element_size)
{
if (accessor->is_sparse)
{
return 0;
const uint8_t* element = cgltf_find_sparse_index(accessor, index);
if (element)
return cgltf_element_read_float(element, accessor->type, accessor->component_type, accessor->normalized, out, element_size);
}
if (accessor->buffer_view == NULL)
{
Expand Down Expand Up @@ -2500,11 +2535,13 @@ cgltf_bool cgltf_accessor_read_uint(const cgltf_accessor* accessor, cgltf_size i
{
if (accessor->is_sparse)
{
return 0;
const uint8_t* element = cgltf_find_sparse_index(accessor, index);
if (element)
return cgltf_element_read_uint(element, accessor->type, accessor->component_type, out, element_size);
}
if (accessor->buffer_view == NULL)
{
memset(out, 0, element_size * sizeof( cgltf_uint ));
memset(out, 0, element_size * sizeof(cgltf_uint));
return 1;
}
const uint8_t* element = cgltf_buffer_view_data(accessor->buffer_view);
Expand All @@ -2520,7 +2557,9 @@ cgltf_size cgltf_accessor_read_index(const cgltf_accessor* accessor, cgltf_size
{
if (accessor->is_sparse)
{
return 0; // This is an error case, but we can't communicate the error with existing interface.
const uint8_t* element = cgltf_find_sparse_index(accessor, index);
if (element)
return cgltf_component_read_index(element, accessor->component_type);
}
if (accessor->buffer_view == NULL)
{
Expand Down
42 changes: 33 additions & 9 deletions gltf/parsegltf.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -66,6 +66,14 @@ static void readAccessor(std::vector<Attr>& data, const cgltf_accessor* accessor
}
}

static void readAccessor(std::vector<Attr>& data, const cgltf_accessor* accessor, const std::vector<unsigned int>& sparse)
{
data.resize(sparse.size());

for (size_t i = 0; i < sparse.size(); ++i)
cgltf_accessor_read_float(accessor, sparse[i], &data[i].f[0], 4);
}

static void fixupIndices(std::vector<unsigned int>& indices, cgltf_primitive_type& type)
{
if (type == cgltf_primitive_type_line_loop)
Expand Down Expand Up @@ -177,11 +185,8 @@ static void parseMeshesGltf(cgltf_data* data, std::vector<Mesh>& meshes, std::ve
Mesh& result = meshes.back();

result.scene = -1;

result.material = primitive.material;

result.extras = primitive.extras;

result.type = primitive.type;

result.streams.reserve(primitive.attributes_count);
Expand All @@ -199,14 +204,27 @@ static void parseMeshesGltf(cgltf_data* data, std::vector<Mesh>& meshes, std::ve
}
else if (primitive.type != cgltf_primitive_type_points)
{
// note, while we could generate a good index buffer, reindexMesh will take care of this
// note, while we could generate a good index buffer here, mesh will be reindexed during processing
result.indices.resize(vertex_count);
for (size_t i = 0; i < vertex_count; ++i)
result.indices[i] = unsigned(i);
}

// convert line loops and line/triangle strips to lists
fixupIndices(result.indices, result.type);

std::vector<unsigned int> sparse;

// if the index data is very sparse, switch to deindexing on the fly to avoid the excessive cost of reading large accessors
if (!result.indices.empty() && result.indices.size() < vertex_count / 2)
{
sparse = result.indices;

// mesh will be reindexed during processing
for (size_t i = 0; i < result.indices.size(); ++i)
result.indices[i] = unsigned(i);
}

for (size_t ai = 0; ai < primitive.attributes_count; ++ai)
{
const cgltf_attribute& attr = primitive.attributes[ai];
Expand All @@ -232,7 +250,10 @@ static void parseMeshesGltf(cgltf_data* data, std::vector<Mesh>& meshes, std::ve
if (attr.type == cgltf_attribute_type_custom)
s.custom_name = attr.name;

readAccessor(s.data, attr.data);
if (sparse.empty())
readAccessor(s.data, attr.data);
else
readAccessor(s.data, attr.data, sparse);

if (attr.type == cgltf_attribute_type_color && attr.data->type == cgltf_type_vec3)
{
Expand Down Expand Up @@ -262,7 +283,10 @@ static void parseMeshesGltf(cgltf_data* data, std::vector<Mesh>& meshes, std::ve
s.index = attr.index;
s.target = int(ti + 1);

readAccessor(s.data, attr.data);
if (sparse.empty())
readAccessor(s.data, attr.data);
else
readAccessor(s.data, attr.data, sparse);
}
}

Expand Down Expand Up @@ -312,11 +336,11 @@ static void parseMeshInstancesGltf(std::vector<Transform>& instances, cgltf_node
for (size_t i = 0; i < count; ++i)
{
if (translation)
cgltf_accessor_read_float(translation, i, instance.translation, sizeof(float));
cgltf_accessor_read_float(translation, i, instance.translation, 4);
if (rotation)
cgltf_accessor_read_float(rotation, i, instance.rotation, sizeof(float));
cgltf_accessor_read_float(rotation, i, instance.rotation, 4);
if (scale)
cgltf_accessor_read_float(scale, i, instance.scale, sizeof(float));
cgltf_accessor_read_float(scale, i, instance.scale, 4);

Transform xf;
cgltf_node_transform_world(&instance, xf.data);
Expand Down