Inheritance problem

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Hello,

I've a problem with my class inheritance. I have class called Texture
which implements the interface IDrawable and the abstract class
APickable.
The Texture-class contains 3 members which looks like this:

GLuint pTextureID;

Size pSize1, pSize2;

Finally... my Texture-class looks like:

class Texture : APickable, IDrawable {
   protected {
      GLuint pTextureID;
      Size pSize, pAnoutherSize;
   }
}

now... I have a second class called Animation which looks like this:

class Animation : Texture {
   private {
      Texture[] pFrames;
   }
   public {
      this(string file, string[] paths...) {
         super(file);
         pFrames ~= this;
         foreach(string cur; paths) {
            pFrames ~= new Texture(cur);
         }
      }

      Size getSize() {
         return pFrames[0].pSize;
      }
   }
}

As I know, pFrames[0].pSize can be called... pSize in the Texture-
class is marked as protected, but I get the following error:

Error: class Texture member pSize is not accessible.

When I mark the protected members of the Texture-class as public, it
works (should be clear), but why do I get this error when mark them
as protected?

I hope anyone can help to solve the problem.