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Thread: .OBJ texture coordinates aren't mapped correctly

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  1. #1
    Junior Member Newbie
    Join Date
    May 2013
    Posts
    4

    Unhappy .OBJ texture coordinates aren't mapped correctly

    This is a cross-post from game-dev because it seems more general to graphical programming than game development.

    I have written a simple .obj parser for my OpenGL game engine that reads vertices, uv's and normals; but when I get to drawing the model in the texture isn't mapped correctly.

    I have tried
    Code :
    uv.y = 1.0f-uv.y
    to get inverted Y axis coordinates as suggested by a few people but my textures are still skewed.

    I know the texture and my rendering are correct because when I render a plane, with hand written texture coordinates and vertices using the same texture, it renders fine. I can render a textured cube by hand fine too.

    I am using an index buffer to store vertex elements and I use the face elements provided by the obj to fill texture coordinate and normal buffers with the correct vectors.

    What is wrong with my parser?


    PARSER CODE:

    Code :
    Model::Model(const string &givenName, const string &filePath){
        name = givenName;
     
        std::ifstream in(MODEL_PATH+filePath, std::ios::in);
        if(!in){
            error("Model \"" + filePath + "\" does not exist");
            return;
        }
     
     
        ModelMeshIndex tempindex;
     
        vector<vec3> normals;
        vector<vec2> uvs;
     
        string line;
        while(getline(in, line)){
            if(line.substr(0,2) == "v "){
                        std::istringstream s(line.substr(2));
                        vec3 v(0.0f);
                        s >> v.x >> v.y >> v.z;
                        data.vertices.push_back(v);
            }
            else if(line.substr(0,2) == "vt"){
                        std::istringstream s(line.substr(2));
                        vec2 v(0.0f);
                        s >> v.x >> v.y;
                        //v.y = 1.0f-v.y;
                        uvs.push_back(v);
            }
            else if(line.substr(0,2) == "vn"){
                        std::istringstream s(line.substr(2));
                        vec3 v(0.0f);
                        s >> v.x >> v.y >> v.z;
                        normals.push_back(v);
            }
            else if(line.substr(0,2) == "f "){
                        std::istringstream s(line.substr(1));
                        char tmp; // For the slashes between elements
                        unsigned short a,b,c, d,e,f, g,h,i;
                        s >> a >> tmp >> d >> tmp >>g;
                        s >> b >> tmp >> e >> tmp >>h;
                        s >> c >> tmp >> f >> tmp >>i;
                        a--; b--; c--; d--; e--; f--; g--; h--; i--;
                        data.index.vertexElements.push_back(a); data.index.vertexElements.push_back(b); data.index.vertexElements.push_back(c);
                        data.index.uvElements.push_back(d);     data.index.uvElements.push_back(e);     data.index.uvElements.push_back(f);
                        data.index.normalElements.push_back(g); data.index.normalElements.push_back(h); data.index.normalElements.push_back(i);
            }
            else if(line[0] == '#') continue;
            else continue;
        }
     
        for(unsigned int i = 0; i < data.index.normalElements.size(); ++i)
            data.normals.push_back(normals[data.index.normalElements[i]]);
     
        for(unsigned int i = 0; i < data.index.uvElements.size(); ++i)
            data.uvs.push_back(uvs[data.index.uvElements[i]]);
     
        //data.uvs.push_back(vec2( 0.0f, 0.0f)); // bottom left
        //data.uvs.push_back(vec2( 0.0f, 1.0f)); // top left
        //data.uvs.push_back(vec2( 1.0f, 0.0f)); // bottom right
        //data.uvs.push_back(vec2( 1.0f, 1.0f)); // top right
     
        good = true;
    }

    Last edited by CoffeeandCode; 05-07-2013 at 10:19 PM.

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