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MarkS

Questions about encapsulation, resource management, global variables* and the like...

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I'm in the middle of writing my first tile engine in C++. I've stuck with C for years and I find it easier. Now that I am switching to C++, I am finding that simple matters are suddenly not so simple.

 

My problem arises from the need to use a resource manager and the fact that global variables are a bad thing in C++. In C, I would just make global arrays of textures and what not and the various functions could access them at will. I'm at a loss how to do this in C++.

 

My design is as such:

 

 

class mesh{
//Stuff
};
 
class sprite{
//Stuff
mesh *sprite_mesh;
};
 
class Tile{
//Stuff
sprite *tile_sprite;
};
 
class tile_layer{
//Stuff
std::vector<tile *> tiles;
std::vector<sprite *> sprites;
};
 
class tile_level{
//Stuff
std::vector<tile_layer *> tile_layers;
resource_manager<texture> *textures;
resource_manager<shader> *shaders;
};

 

 

Of course, the actual code is a bit more involved. What I am having trouble with is how to access the resource managers located in the tile_level class from the mesh class. Regardless if the resources are loaded during the construction of the tile_level object or during the loading of the individual meshes, when I call the mesh's render function, I need it to be able to access the resource managers.

 

The only way I can think of is to pass a pointer to the managers up the chain through the constructors, however, this would require needless pointers to the managers in the tile_layer and sprite classes. There has got to be a simple way to do this, and I know it is my unfamiliarity with C++ that is making this difficult.

 

How would I go about this in a C++-correct manor?

 

...Don't know why there is an asterisk in the titlehuh.png... 

Edited by MarkS

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Don't pass the "managers", pass the constructed objects. A tile isn't aware of managers, just construct the tile with the appropriate texture and/or shader. It can pass these to any inner objects that store them.

 

Another way is to avoid storing these on a per tile basis. A tile might have a reference to a "tile type", which might contain information about whether the tile is passable, etc. You can store the graphical representation of the tile here too. Note that mixing your rendering objects into your game objects can complicate some designs (though it can simplify some games too, YMMV).

 

A final note, prefer values to pointers, and prefer smart pointers to raw pointers.

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Why do the textures need to be in a manager?

Because most tile-based games use a small subset of textures, but those textures are drawn hundreds of times per level. If I load the same texture for each tile that needs it, the memory demands of this engine will be astronomical. By putting the resources in a manager, only one instance of a texture is loaded and it can then be accessed by any tile and/or sprite that needs it.

 

 

Don't pass the "managers", pass the constructed objects. A tile isn't aware of managers, just construct the tile with the appropriate texture and/or shader. It can pass these to any inner objects that store them.
 
Another way is to avoid storing these on a per tile basis. A tile might have a reference to a "tile type", which might contain information about whether the tile is passable, etc. You can store the graphical representation of the tile here too. Note that mixing your rendering objects into your game objects can complicate some designs (though it can simplify some games too, YMMV).
 
A final note, prefer values to pointers, and prefer smart pointers to raw pointers.
 
I'm using boost's smart_ptr. I just didn't want to write "boost::smart_ptr" over and over in the example.
 
If I pass the constructed object, wouldn't that defeat the purpose of having a resource manager? I could just as easily load the texture and shader each time I load a mesh, but the point is to reduce or eliminate redundant resource allocation.
 
Also, I am not storing the resources on a per tile basis. The resources are stored in the lowest level class, tile_level, as resource pools and accessed by the higher-level classes. Maybe I am misunderstanding you?
Edited by MarkS

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Why do the textures need to be in a manager?

Because most tile-based games use a small subset of textures, but those textures are drawn hundreds of times per level. If I load the same texture for each tile that needs it, the memory demands of this engine will be astronomical. By putting the resources in a manager, only one instance of a texture is loaded and it can then be accessed by any tile and/or sprite that needs it.

 

Each tile could simply have a pointer to the texture you want it to use. A pointer only takes up the size of an int.

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I would have a list of tile definitions, each having a pointer to the texture it uses.

Each tile would contain only an index to the tile definition (tile type)

When rendering you get the texture from the tile definitions using the tiles index thing.

The textures can be stored separately, in a manager, whatever works.

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I would have a list of tile definitions, each having a pointer to the texture it uses.

Each tile would contain only an index to the tile definition (tile type)

When rendering you get the texture from the tile definitions using the tiles index thing.

The textures can be stored separately, in a manager, whatever works.

That is how I've done it in the past. The tile_layer class had a 2D array of unsigned longs, each an index into the texture list. There wasn't a tile class. However, I am breaking that tried and true method and allowing tiles to be any shape and size, as well as having the ability to move and be animated. It complicates things quite a bit. The tiles are composed of 3D meshes, and may have diffuse, normal and specular maps, along with various shaders, as needed. It isn't easy (possible?) to do a simple assignment as I have previously done.

 

I think HappyCoder said it best. I think I am complicating things more than I need to with the resource allocation. I'm going to rethink this a bit.

Edited by MarkS

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...and the fact that global variables are a bad thing in C++. In C, I would just...

Don't misunderstand this - global variables are as "bad" in C as they are in C++. It has nothing to do with the language.

"Bad" is obviously the wrong term. There are advantages and disadvantages to using global state and in general the disadvantages tend to outweigh the advantages in non-trivial projects.

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To reinforce what Aardvajk said, its not that global state is a a better idea in C than C++, I think its more to the point that the mechanisms for encapsulation in C are not terribly obvious for less experienced programmers, and so many C codebases of smallish size kind of become this amorphous "pile of code" that has far less rigid structure than a typical C++ codebase of similar size. This lack of structure is bad, but it ends up seeming more able to cope with unforeseen changes as a result -- C code in this less-structured style is more fly-by-the-seat-of-your-pants hackable, while C++ tends to require at least a broad plan up-front, and departures from said plan can be done, but require a new plan. Good C code is the same way -- as a rule of thumb, odds are that if you make a significant change and didn't need a new plan as a result, its because you didn't have a plan to begin with.

 

There's also the issue that less-experienced C++ programmers tend to over use or misuse the OOP features of C++, deep inheritance hierarchies for example, or using inheritance where composition should be preferred.

Edited by Ravyne

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Why do the textures need to be in a manager?

Because most tile-based games use a small subset of textures, but those textures are drawn hundreds of times per level. If I load the same texture for each tile that needs it, the memory demands of this engine will be astronomical. By putting the resources in a manager, only one instance of a texture is loaded and it can then be accessed by any tile and/or sprite that needs it.

 

Each tile could simply have a pointer to the texture you want it to use. A pointer only takes up the size of an int.

 

And that is exactly what he is saying. But, in order to avoid loading the same texture over and over, somewhere you need an object with a list of loaded texture, so you can decide if the requested texture is already there (in the list) and return a pointer to it,or needs to be loaded from disk. Thus you need a manager that hides away all this, and when you need a texture you just call resourceManager->getTexture("blabla"); and all the caching is hidden inside there.

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