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Indices of an obj file

1 post in this topic

Hello there,

I'm trying to load an .obj wavefront file (for simplicity reasons - later I want to read other - better - fromats).

The models are exported with Blender 2.68a.

I assume that the vertices are read correctly - the problem is rather in the index generating part as this picture suggests:


objindices.png(The left model was recreated from the Input Assembler input)


The main problem with loading the indices is similar to this:



My solution to the problem is to look in each face definition if the vertex already exists and then add the corresponding index.

Otherwise the new vertex is added to a list and then add a the index (wich is the size of the vertex array...)

//Split the line with delim ' ' (Space) to gather the data of each vertex
	vector<string> triangle_data = Split(line,' '); //Vetor of vertex data
	//Only triangles are supported!
	if (triangle_data.size() != 4) //1st element is a empty string!
		throw invalid_argument("OBJ file contains primitive data other than Triangle Lists. (NGON, L                ines, ...)");
	//Read the vertices
	for (int iVertex = 0; iVertex < 3; iVertex++) //Process each vertex
		one vertex data looks like this:
		5/8/9 or 6//4
		string vertex_data = triangle_data.at(iVertex);
		if (vertex_data == "")
		//Split vertex_data with delimeter '/' to gather indices of position and normal
		vector<string> vertex_index_data = Split(vertex_data);
		//Get Position data
		UINT position_index = stoi(vertex_index_data.at(0)) - 1;
		UINT normal_index = stoi(vertex_index_data.at(2)) - 1;
		if (position_index >= position_data.size() || normal_index >= normal_data.size())
			continue; //We should never get here
		XMFLOAT3 pos = position_data.at (position_index);
		XMFLOAT3 nrm = normal_data.at (normal_index);
		//Assemble the vertex
		VertexFormats::VertexPositionNormal vertex;
		vertex.position = pos;
		vertex.normal = nrm;
		//Update the vertex and index vectors
		//Check if the vertex already exists
		auto vertex_pos = find(vertices.begin(), vertices.end(), vertex);
		if (vertex_pos == vertices.end())
			//The vertex does not exist - add it to the vertex list
			//Update the index list
			indices.push_back(vertices.size() - 1);
			//the vertex already exists - add the corresponding index
			indices.push_back(vertex_pos - vertices.begin());
	} //for each vertex

(The whole code of the class is attached.)


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I found the problem(s):

1: I only read 2 vertices instead of 3 per triangle

//Only triangles are supported!
	if (triangle_data.size() != 4) //1st element is a empty string!
		throw invalid_argument("OBJ file contains primitive data other than Triangle Lists. (NGON, Lines, ...)");
	//Read the vertices
	//for (int iVertex = 0; iVertex < 3; iVertex++) //<---- Wrong
for (int iVertex = 1; iVertex < 4; iVertex++) //Process each vertex

2: I skip every secound triangle, since I jump to the next line after processing one triangle, but since I use getline the '\n' char is already read.

if (data_type == "f") //current line contains a triangle specification
			ReadFace(file, positions, normals, vertices, indices);
			continue; //ReadFace does already read the \n char!
		//Simply ignore other commands for now
#undef max
		//Skip the line
		file.ignore(numeric_limits<streamsize>::max(), '\n');
#define max

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