part1.md

Part 1: Loading the data

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Parsing the stl data is not that hard. Now that we know the structure of the file, we can define the structure in the code.

struct Facet
{
public:
    struct vec3f normal;
    struct vec3f vertices[3];
    uint16_t attributes;

public:
    void print()
    {
        LOG("Normal: " << normal.to_string());
        for (int i = 0; i < 3; i++)
        {
            LOG("Vert " << i << ": " << vertices[i].to_string());
        }
    }
}__attribute__((packed));

The vec3f structure is defined as

struct vec3f
{
public:
    float x;
    float y;
    float z;
        
public:
    std::string to_string() 8bada1eaf2f49277e3cd2382f66fc9dfbbdc8727
    {
        return std::to_string(x) + " " + std::to_string(y) + " " + std::to_string(z);   
    }
    
};

There are two things important here. First of all, the attribute((packed)) is beneficial for this to work. This attribute means that the compiler will not add any padding to pad the bytes to 4 byte marks. That would happen here and if you would do a sizeof(struct Facet) you would get 52 instead of the correct 50. And secondly, the print() function that I added does not increase the size of the struct at all. It is just there for testing purposes.

I did also add a facet array to the StlParser and a parse() function.

class StlParser
{
private:
    std::ifstream m_stlfile;
    // new:
    std::vector<Facet> m_facet_array;
public:
    StlParser(std::string file);
    ~StlParser();
    // new:
    void parse();

};

We will save the facet data in this vector.

In the stlparser.cpp I implemented the parse function. It simply reads the data into the array.

void StlParser::parse()
{
    LOG("parsing file");
    // The first 80 bytes are a unimportant ascii, however
    // for testing we will print it anyway

    char header[80];
    m_stlfile.read(header, 80);
    LOG("File header reads: '" << header << "'");

    // Read the facet count.
    uint32_t facet_count;
    m_stlfile.read((char*) &facet_count, 4);

    LOG("Facet count: " << facet_count);

    // Initialize the facet array that will be used to keep all the facets.
    m_facet_array = std::vector<Facet>(facet_count);

    for (uint i = 0; i < facet_count; i++)
    {
        m_stlfile >> (char*) &(m_facet_array[i]);
        m_facet_array[i].print();
    }
}

Now to test this add i changed the main.cpp file a bit, i changed the StlParser(...) call with

    std::string s(argv[1]);
    StlParser parser(s);
    parser.parse();

And normally if you run the code with tests/stls/cube.stl as parameter. You should get the header, facet count and 12 facets printed to the screen.