Bim 272 converter packed metadata from gltfpack and output metadata file #1

pirlande-fw · 2024-08-28T15:01:11Z

This PR aims at generating an additional output file from the gltfpack utility to keep track of the meshes that are merged together.

The aim is to optionally use this information on our mobile apps to show objects properties. Using gltfpack is very helpful as it reduces the draw count by merging meshes together, which makes complex models viewable on mobile. The caveat is that we lose the meshes metadata information.

How it is done

There are several key pieces that follow the order of commits:

at parsing time (in parsegltf.cpp), we first retrieve the parent node from meshes, as parent nodes carry out the name used to retrieve properties. But a parent node can have several mesh child nodes, so we also keep the index of the mesh from its parent node. Both pieces of information are stores into the main Mesh struct.
at processing time (in gltfpack.cpp), we disable one optimization using a new option named -kmpn (for keep mesh parent nodes). This option makes sure the merged mesh's parent nodes are kept as they are the ones that carry out the names used to retrieve properties. At the end, we have the same number of parent nodes as merges meshes. Their names are generated dynamically, from the information retrieved at parsing time, and we write them into the merged mesh's parent nodes.
the key step is the merging one (in mesh.cpp), where a source mesh is merged into a target mesh. At this step, we keep two pieces of information into the target mesh:
- the parent node name of the source mesh
- the index_offset where the triangle vertice positions of the source mesh are copied over into the target mesh
finally, we print the metadata information into an output file, using a new option named -mmi (for merge mesh information). Here, we just iterate over the merged meshes, and format the useful information stored at the previous step.

To illustrate, let's take this GLTF file example:

 "meshes": [
    /* mesh with 12 indices */
    {
      "primitives": [
        ...
      ]
    },
    /* mesh with 36 indices that will be merged into the first one */
    {
      "primitives": [
        ...
      ]
    },
    /* mesh with 9 indices that will be merged into the first one */
    {
      "primitives": [
        ...
      ]
    },
  ],
  "nodes": [
    {
      "mesh": 0,
    },
    {
      "mesh": 1,
    },
    {
      "mesh": 2,
    },
    {
      "name": "0yiBM2NAH96xSSnOnrhhld",
      "children": [0, 1]
    },
    {
      "name": "3j913Y4av3qOaiLIYT4b6p",
      "children": [2]
    }
  ]

The output metadata file should contain:

{
  "0yiBM2NAH96xSSnOnrhhld_0": {   // note the _0 that indicates the first child mesh of 0yiBM2NAH96xSSnOnrhhld
    "0": "0yiBM2NAH96xSSnOnrhhld", // for the 2 first meshes (12+36=48 indices)
    "48": "3j913Y4av3qOaiLIYT4b6p"  //  3rd mesh
}

On the client side, when the merged mesh 0yiBM2NAH96xSSnOnrhhld_0 is touched, we'll need to retrieve the triangle that was selected in the mesh. From the triangle, we can retrieve its vertices, then its corresponding indices. If we find indices 51, 52, 53 for example, we know that it's after 48, so that's the initial 3rd mesh that was selected. We get 3j913Y4av3qOaiLIYT4b6p and can display the corresponding property 🙌.

How to read

Read by commit

How to test

To build, follow instructions at the end of this page.
Take an input glb file and run this command line:

./gltfpack -i input.glb -o packed.glb -vp 16 -vn 16 -vc 16 -vpf -cc -v -kmpn -mmi metadata.json

See the produced output.json file

…es carry out names

…tion

pirlande-fw · 2024-08-28T20:31:57Z

@tsanghrajka @mehulshinde I'm not sure how familiar you are with C++.
Happy to go through this PR live as needed.

tsanghrajka

Looks great overall!
Thanks for the detailed description and explanation @pirlande-fw 🙏 🙌

mehulshinde

Thank you for the detailed explanation @pirlande-fw. Looks good 👏👏 Left some super nit around bracket style.

mehulshinde · 2024-08-29T20:02:29Z

gltf/gltfpack.cpp

@@ -183,6 +189,70 @@ static void printImageStats(const std::vector<BufferView>& views, TextureKind ki
 		printf("stats: image %s: %d bytes in %d images\n", name, int(bytes), int(count));
 }

+static bool printMergeMetadata(const char* path, const std::vector<Mesh>& meshes) {


nit: I think the default style of these cpp files is to follow Allman style for curly brackets. Although I am team K&R, might want to keep things consistent. This is super minor so feel free to disregard this and other instances of this.

Thx, I did not even realize!
Addressed all comments in 538a003

mehulshinde · 2024-08-29T20:03:05Z

gltf/gltfpack.cpp

@@ -555,11 +625,17 @@ static void process(cgltf_data* data, const char* input_path, const char* output
 	{
 		const Mesh& mesh = meshes[i];

+		std::string mesh_name = std::string();
+		if (settings.keep_mesh_parent_nodes) {


nit: Allman style brackets

mehulshinde · 2024-08-29T20:03:21Z

gltf/gltfpack.cpp

-		// skip all meshes that we've written in this iteration
-		assert(pi > i);
-		i = pi - 1;
+		if (!settings.keep_mesh_parent_nodes) {


nit: Allman style brackets

mehulshinde · 2024-08-29T20:03:45Z

gltf/mesh.cpp

@@ -257,11 +257,15 @@ static void mergeMeshes(Mesh& target, const Mesh& mesh)

 	size_t index_count = mesh.indices.size();

-	for (size_t i = 0; i < index_count; ++i)
+	for (size_t i = 0; i < index_count; ++i) {


nit: Allman

mehulshinde · 2024-08-29T20:03:57Z

gltf/parsegltf.cpp

@@ -186,6 +205,12 @@ static void parseMeshesGltf(cgltf_data* data, std::vector<Mesh>& meshes, std::ve

 			size_t vertex_count = primitive.attributes_count ? primitive.attributes[0].data->count : 0;

+			// save the parent node info to the mesh
+			if (nodes_to_child_meshes_map_it != nodes_to_child_meshes_map.end()) {


nit: Allman

mehulshinde · 2024-08-29T20:04:10Z

gltf/write.cpp

 {
 	comma(json);
 	append(json, "{\"mesh\":");
 	append(json, mesh_offset);
+	if (!name.empty()) {


nit: Allman

pirlande-fw added 8 commits August 28, 2024 14:57

Extract parent node to mesh information in parser

ecce1d0

Add an option to keep parent nodes while merging nodes, as parent nod…

7efb761

…es carry out names

Write the mesh name into corresponding node when provided

5a04cfc

Save merge information into target mesh

f9934f6

Add an option to add an output file containing merge metadata informa…

3a3fc7d

…tion

Factorize mesh unique identifier computation

5721396

Fix output optimization to avoid duplicating the first mesh info

852f22b

Rename metadata output option to -mmi

cf20d35

pirlande-fw requested review from mehulshinde and tsanghrajka August 28, 2024 20:30

pirlande-fw assigned jayrave Aug 28, 2024

tsanghrajka approved these changes Aug 29, 2024

View reviewed changes

mehulshinde approved these changes Aug 29, 2024

View reviewed changes

Apply Allman style for curly brackets

538a003

pirlande-fw merged commit 8c9fa1b into master Aug 30, 2024

pirlande-fw deleted the BIM-272-converter-packed-metadata-from-gltfpack-and-output-metadata-file branch August 30, 2024 13:55

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Bim 272 converter packed metadata from gltfpack and output metadata file #1

Bim 272 converter packed metadata from gltfpack and output metadata file #1

pirlande-fw commented Aug 28, 2024 •

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Bim 272 converter packed metadata from gltfpack and output metadata file #1

Bim 272 converter packed metadata from gltfpack and output metadata file #1

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pirlande-fw commented Aug 28, 2024 • edited Loading

How it is done

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How to test

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pirlande-fw commented Aug 28, 2024 •

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