Parse .OBJ file for OpenGL

parse_obj.c

MyVertex* parseObjFile(const char* file, int* faces, int* lines) {
    FILE* fp = NULL;
    errno_t ferr = fopen_s(&fp, file, "r");
    fseek(fp, 0, SEEK_END);
    long size = ftell(fp);
    fseek(fp, 0, SEEK_SET);
    char* buffer = (char*)malloc(size + 1);
    fread(buffer, 1, size, fp);
    buffer[size] = '\0';

    int numVertices = 0;
    int numFaces = 0;
    int numLines = 0;
    char* start = buffer;
    for (int i = 0; i < size;) {
        // Search for the end
        int lineLength = 0;
        while (start[lineLength++] != '\n');

        float vx, vy, vz;
        int f1, f2, f3, t1, t2, t3;
        if (sscanf_s(start, "v %f %f %f", &vx, &vy, &vz) == 3) {
            numVertices++;
        } else if (sscanf_s(start, "f %d/%d %d/%d %d/%d", &f1, &t1, &f2, &t2, &f3, &t3) == 6) {
            numFaces++;
        }
        else if (sscanf_s(start, "l %d %d", &f1, &f2) == 2) {
            numLines++;
        }

        assert(lineLength >= 0);
        start += lineLength;
        i += lineLength;
    }

    // Temporary for holding vertex definitions
    MyVertex* verticesList = (MyVertex*)malloc(sizeof(MyVertex) * numVertices);
    // "Actual" vertices
    int numActualVertices = numFaces * 3 + numLines * 2;
    MyVertex* vertices = (MyVertex*)malloc(sizeof(MyVertex) * numActualVertices);

    start = buffer;
    int vertex = 0;
    for (int i = 0; i < size;) {
        // Search for the end
        int lineLength = 0;
        while (start[lineLength++] != '\n');

        float vx, vy, vz;
        int f1, f2, f3, t1, t2, t3;
        if (sscanf_s(start, "v %f %f %f", &vx, &vy, &vz) == 3) {
            verticesList[vertex].x   = vx;
            verticesList[vertex].y   = vy;
            verticesList[vertex++].z = vz;
        }

        start += lineLength;
        i += lineLength;
    }

    int currentMaterial = 0;
    start = buffer;
    vertex = 0;
    for (int i = 0; i < size;) {
        // Search for the end
        int lineLength = 0;
        while (start[lineLength++] != '\n');

        float vx, vy, vz;
        int f1, f2, f3, t1, t2, t3;
        if (sscanf_s(start, "f %d/%d %d/%d %d/%d", &f1, &t1, &f2, &t2, &f3, &t3) == 6) {
            vertices[vertex] = verticesList[f1 - 1];
            setMaterial(&vertices[vertex++], currentMaterial, t1 - 1);

            vertices[vertex] = verticesList[f2 - 1];
            setMaterial(&vertices[vertex++], currentMaterial, t2 - 1);

            vertices[vertex] = verticesList[f3 - 1];
            setMaterial(&vertices[vertex++], currentMaterial, t3 - 1);

            assert(vertex <= numActualVertices);
        }
        else if (sscanf_s(start, "l %d %d", &f1, &f2) == 2) {
            vertices[vertex] = verticesList[f1 - 1];
            setMaterial(&vertices[vertex++], currentMaterial, 0);

            vertices[vertex] = verticesList[f2 - 1];
            setMaterial(&vertices[vertex++], currentMaterial, 0);

            assert(vertex <= numActualVertices);
        }
        else if (sscanf_s(start, "usemtl mtl_%X", &currentMaterial) == 1) {
            // TODO: Make sure currentMaterial doesn't change if no match
        }
        start += lineLength;
        i += lineLength;
    }

    free(verticesList);
    free(buffer);

    *faces = numFaces;
    *lines = numLines;
    return vertices;
}