Question

I have an awkward question. I think it’s impossible but I need to know for sure. It’s a bit of an odd request, but I need my child classes to share the SAME Pixels vector from the parent class.

Basically, I want to create an instance of Image class. That Image class will hold Pixels for both Bitmap and Png Class so that if I need to convert from Bitmap To PNG and Vice-versa, they use the same vector rather than me creating both Bitmap and PNG classes.

class Image
{
    private:
        std::vector<RGB> Pixels;
};



class Bitmap : Image
{
    public:
        Bitmap() : Image() {};
};


class Png : Image
{
    public:
        Png() : Image() {};
};

Such that when I do:

int main()
{
    Image Img();

    Img.GetBitmapPixels();  //This
    Img.GetPngPixels();     //And this, return the same Pixels Vector.

    Bitmap Foo = Img.ToPng();
    Png Moo = Img.ToBitmap();
    //Such that both Foo and Moo have the exact same underlying Pixels Vector.
}

Currently my classes look like:

class Bitmap
{
    private:
        std::vector<RGB> Pixels;

    public:
        Bitmap();
        std::vector<RGB> GetPixels() {return Pixels;}
        void SetPixels(std::vector<RGB> Pixels) {this->Pixels = Pixels;}
};

class Png
{
    private:
        std::vector<RGB> Pixels;

    public:
        Png();
        std::vector<RGB> GetPixels() {return Pixels;}
        void SetPixels(std::vector<RGB> Pixels) {this->Pixels = Pixels;}
};

And to convert from one to the other, I have to do:

int main()
{
    Bitmap Bmp();
    Png PNG();

    PNG.SetPixels(BMP.GetPixels);   //BMP has to COPY PNG's Pixels and vice-versa..
}

It’s kind of a stupid question. I just don’t want to copy pixels. I just want to be able to convert between the two classes without any copying as both classes hold an std::vector Pixels member and the data is aligned the same.

I guess I’m trying to be able to do: PNG.SaveAsBitmap(…); Or BMP.SaveAsPNG(…); without creating a new instance of the other.

How can I avoid copying/creating and making a new instance of the other class I’m converting to? Can I have classes that inherit from eachother?

Answer 1

I may be oversimplyfying this. How are you loading your data? If it is the same for each image type could you have a load in the image class and just overload the Translation functions. I am not an expert on image data but could you do something similiar to:

   public Image
    {
       private Pixels data;
       public void GetPixels();
       public virtual Pixels ToFormat(FormatEnum format);
    }

    public Bitmap:Image
    {
        public override Pixels ToFormat(FormatEnum format)
        {
            switch(format){  
                case FormatEnum.Bitmap:return data;break;
                case FormatEnum.Png:return doSomethingElse();break;
            }
        }
    } 

   int main()
   {
      Image Img();

      Img.GetPixels();

       Bitmap Foo = Img.ToFormat(Format.BitMap);
       Png Moo = Img.ToFormat(Format.Png);

   }