"Rafal Maj" <no@address.invalidwrote in message
news:f3**********@inews.gazeta.pl...
>
Say we have a class Model (a 3d model) and class Texture (representing an
Texture).
Model have a texture, Model can be Drawed. Texture have method that
returns
data needed for drawing.
class Texture {
public:
// openGl data here
glInt GetInt();
};
class Model {
public:
Texture *tex;
void Draw() {
glInt x = tex->GetInt();
// ...
}
};
And all is well.
But now - say I want to make this design more flexible, to have
opengl-texture (and way of drawing for the monster)
and directX-texture (and directX way of drawing of the monster).
So I will make Texture a base class, and move OpenGL stuff into TextureOGL
etc.
class Texture { public: };
class TextureOGL : public cTexture
{ public: /* opengl data */ glInt GetInt(); };
// more Texture*
THE PROBLEM: but what then happens to the monster?
1) how to add methods for drawing in different ways (I want that to be
choosed in runtime)
2) how to access the texture
My possible solutions
Solution-1 - only child have texture
class Texture { public: };
class TextureOGL : public cTexture { public: /*...*/ glInt GetInt(); };
class cMonster { virtual void Draw()=0; };
class cMonsterOGL : public cMonster { public:
cTextureOGL *tex;
virtual void Draw() { tex->GetInt(); /*...*/ }
};
Almost ideal but that doesnt modell that EVERY monster always have SOME
texture (and that information migt be needee)
I'm not sure what it means when you say every monstre has SOME texture.
What's the relationship between an OpenGL texture and a DirectX texture?
Are they actually related, or just somewhat similar in concept? If they're
not related, then perhaps thinking of them as the same thing is wrong to
begin with.
>
Solution-2
class Texture { public: virtual string Name(); };
class TextureOGL : public cTexture { public: /*...*/ glInt GetInt(); };
class cMonster { public: cTexture *tex; virtual void Draw()=0;
void GeneralUseOfTexture() { MsgBox(tex->Name()); }
};
class cMonsterOGL : public cMonster { public:
virtual void Draw() {
dynamic_cast<cTextureOGL>(tex)->GetInt(); /*...*/
// else/catch - wrong dynamic cast - print error "Wrong
texture!"
}
};
That models all informations and allow general use of texture ->Name();
The problem is - it uses a dynamic_cast with is consider not so good, also
I
wonder about speed implications.. upcast is fast and O(1) or not really?
Other solutions?
Perhaps using templates... but writting entire Monster<Timplementation
inside header .h is not too good since its complicated class.
Also it would be not so easy to have a std::vector of monsters etc.
Perhaps what you need is to separate the monster and the texture from each
other? After all, changing how the monster is rendered shouldn't have to
change the monster itself. (Especially if you can change how they're drawn
at run-time.)
One solution would be to make another object which contains (or points to) a
monster and a texture, thus associating the two. That owner monster/texture
object would know how to Draw(), using the texture type it's designed for
and monster it's associated with.
So, you might create a vector of OpenGL monster/texture owner objects, or
you might create a vector of DirectX monster/texture owner objects,
depending on the user choice (or whatever).
And besides Draw(), any other manipulations that involve both the monster
and the texture could be done via virtual members of the appropriate type of
monster/texture owner object. And the monster would hold a pointer to the
base-class (possible pure abstract?) of the monster/texture owner, so calls
from either a Monster or one of the Texture classes would be polymorphic,
removing any concern on the Monster's part as to what type of owner object
(and thus what type of texture) it's working with.
Here's an example, where the textures need not be related at all:
class Monster;
class Texture_OpenGL;
class Texture_DirectX;
class MonsterTextureOwner
{
Monster* pMonster;
...whatever...
virtual void DrawMonster() = 0;
virtual ~MonsterTextureOwner();
};
class MonsterTextureOwner_OpenGL
{
Texture_OpenGL textureOGL;
...
virtual void DrawMonster();
...
~MonsterTextureOwner_OpenGL();
};
class MonsterTextureOwner_DirectX
{
Texture_DirectX textureDX;
...
virtual void DrawMonster();
...
~MonsterTextureOwner_DirectX();
};
class Monster
{
MonsterTextureOwner* pOwner;
...
void Draw() { if (pOwner) pOwner->DrawMonster() }
};
-Howard
