Home » Community » Forums » » A Singleton Texture Manager for OpenGL
  Intel sponsors gamedev.net search:   
[Control Panel] [Register] [Bookmarks] [Who's Online] [Active Topics] [Stats] [FAQ] [Search]

Add Forum to Favorites |  Send Topic To a Friend | View Forum FAQ | Track this topic
 Last Thread Next Thread 
 A Singleton Texture Manager for OpenGL
Post Reply 
Reply Quoting This MessageEdit Message mother    Member since: 10/3/2000  From: Canada
 Posted - 7/18/2001 3:11:36 PM
Great article. One suggestion, though:

To decrease the chance that a singleton class is used incorrectly, the constructor(s) could be made private. That way, an error is generated at compile time if an instance of the singleton is instantiated.

For example:

class Singleton {
public:
static Singleton &getInstance() { return _instance; }
private:
Singleton();
~Singleton();
static Singleton &_instance;
};

Singleton &Singleton::_instance;

void main()
{
// Compile-time error, since the ctor is private.
Singleton s;

// Compile-time error, since the ctor is private.
Singleton *s = new Singleton;
}
 User Rating: 1059   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message Deifante    Member since: 3/8/2000  From: Calgary, Canada
 Posted - 7/18/2001 3:41:18 PM
Great.. but how then is one to get the one instance that is needed for the program?
 User Rating: 1015   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message mother    Member since: 10/3/2000  From: Canada
 Posted - 7/18/2001 3:45:58 PM
void main()
{
Singleton &s = Singleton::getInstance();
}
 User Rating: 1059   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message mother    Member since: 10/3/2000  From: Canada
 Posted - 7/18/2001 3:46:04 PM
void main()
{
Singleton &s = Singleton::getInstance();
}
 User Rating: 1059   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message Sly    Member since: 7/28/2000  From: Brisbane, Australia
 Posted - 7/18/2001 10:51:23 PM
What is the advantage to using a singleton class in this case? If you only want one instance of it, then why do you need a class at all?

Public stuff goes in the header...
  
void texInitialize (void);
void texDestroy (void);

// Usage / Implumentation

int texLoadTexture (const char *szFilename, int nTextureID = -1);
int texLoadTextureFromMemory (unsigned char *pData, int nWidth, int nHeight, int nBPP, int nTextureID = -1);

void texFreeTexture (int nID);
void texFreeAll (void);

// Debug / Utilitarian

char *texGetErrorMessage (void);
	
int texGetNumTextures (void);
int texGetAvailableSpace (void);
int texGetTexID (int nIndex);


Private stuff goes in the source file. This is a lot simpler in my opinion. No classes, no references, guaranteed no multiple instances, just good old C.

Steve 'Sly' Williams  Code Monkey  Krome Studios
 User Rating: 1003   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message mother    Member since: 10/3/2000  From: Canada
 Posted - 7/19/2001 12:14:04 AM
You're absolutely right. Doing it in straight C will give the same effect. There are advantages to making a singleton a class, though.

For instance, if requirements change (as they often do), and multiple instances are needed, you simply need to remove the getInstance() method, and make the constructor(s) public. In other words, it's trivial to convert a singleton class into a regular class.
 User Rating: 1059   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message Deifante    Member since: 3/8/2000  From: Calgary, Canada
 Posted - 7/19/2001 11:25:28 AM
I don't get it. If you just refernce the static pointer you still don't have an actual instaniation of the class. Un less when you define the static memeber you explicitly make the class (if i'm makeing sence here);
 User Rating: 1015   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message Outworlder    Member since: 3/3/2000  From: Fortaleza, Brazil
 Posted - 7/19/2001 9:28:33 PM
Another advantage of the singletons is that all functions that deal with a particular subject are contained in a class. Ive done some projects that had a lot of functions. It was just a pain in the a**, and the clarity of the code suffered a lot. (Imagine that):

  

// Global variables

int blah,bleh,blih,bloh,bluh;
(...)

// Function declarations


void somefunction();
void someotherfunction();
something function_that_gets_anything_and_returns_something();
(...)


It always get messy. No matter how you organize it. It is still an organized mess.

Gaiomard Dragon
-===(UDIC)===-

Edited by - Outworlder on July 19, 2001 9:31:36 PM
 User Rating: 974   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message Marvin    Member since: 7/20/2001  From: United Kingdom
 Posted - 7/20/2001 5:36:25 PM
oki, so ive loaded my texture into the texture manager, how do i bind it? examples please, thanks
 User Rating: 1017   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message CodeSmith    Member since: 6/28/2001  From: San Antonio, USA
 Posted - 7/21/2001 5:27:17 PM
It all depends on HOW you loaded your texture with the class, if YOU want to deal with the OpenGL texture ID's then you would do it as normal AKA


TEXMANAGER.LoadTexture ("foobar.tga", FOOBAR_TEXTURE);
glBindTexture (GL_TEXTURE_2D, FOOBAR_TEXTURE);


Or if you want THE CLASS to handle the texture IDs

int nFoobarTex = TEXTUREMANAGER.LoadTexture ("foobar.tga");
glBindTexture (GL_TEXTURE_2D, nFoobarTex);


I belive what your looking for is in the return value.

hope that helps

-The guy that wrote the tutorial

CodeSmith the Pixel Pusher
www.cs.trinity.edu/~csmith8
 User Rating: 1015   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message Gyzmo    Member since: 9/18/1999  From: Tiberia
 Posted - 7/22/2001 7:50:28 AM
The way the singleton is written now can create problems if there is another singleton which requires the use of the texture singleton as static initialisation is currently not necessarily in-order, a better (imho) solution would be to initialize the object on the first call to getInstance() i.e.:

  
static Singleton &getInstance()
{
    static Singleton _instance;
    return _instance;
}


This way you can be sure the object is instantiated the first time getInstance is called.

Gyzmo
================================================
two wrongs don't make a right, three lefts do
 User Rating: 1041   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message WarMage    Member since: 6/8/2001  From: GNU is not Eunuchs!!
 Posted - 7/22/2001 8:08:22 PM
Of course a single texture manager is going to make sense . You can go one further and within CglTexManager, define subclasses - aliases, really - for CglModelTexManager, CglWorldTexManager, CglDecalTexManager, and so forth.

These "middle managers" are just pretty (inter)faces to help classify your texture lists. By this example, CglModelTexManager::BindTexture("ModelXSkin.tga") would simply call the superclass CglTexManager::BindTexture("ModelXSkin.tga", nTex_MODEL), where nTex_MODEL is then returned to CGlModelTexManager, who then manages it's own list when it comes time to do CglModelTexManager::DeleteAll().

Sweet, huh?
<rant>

The only thing that bugs me is the word "Singleton". Why does an instance of a GLOBAL STATIC CLASS get its own nifty name? Capitalised, even? do you capitalize Internet? I hope not, since it isn't a proper noun.

Frankly if somebody says to me "I built a Singleton component to do X.." and I got guys in my shop that have been doing (godlike) code for 20 years going "What the hell is the Singleton Class?", then that says to me this is just another fancy name they give so that the kids with degrees can show off in front of the experienced old fogies...
</rant>

------------
-WarMage
...ummmm, yeah. that one.

Edited by - WarMage on July 22, 2001 8:09:52 PM
 User Rating: 1015   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message CodeSmith    Member since: 6/28/2001  From: San Antonio, USA
 Posted - 7/22/2001 10:13:46 PM
quote:
Original post by Gyzmo
The way the singleton is written now can create problems if there is another singleton which requires the use of the texture singleton as static initialisation is currently not necessarily in-order, a better (imho) solution would be to initialize the object on the first call to getInstance() i.e.:


your 100% right, that IS a better way to do it. However if you just leave it as a static member you have absolutley no control over initialization and deconstruction. So yeah, it is MUCH MUCH MUCH cleaner but with the sacrifice of alittle control



CodeSmith the Pixel Pusher
www.cs.trinity.edu/~csmith8
 User Rating: 1015   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message Vetinari  Moderator Emeritus  Member since: 1/22/2000  From: USA
 Posted - 7/22/2001 10:52:26 PM
quote:
Original post by CodeSmith
your 100% right, that IS a better way to do it. However if you just leave it as a static member you have absolutley no control over initialization and deconstruction. So yeah, it is MUCH MUCH MUCH cleaner but with the sacrifice of alittle control

I believe that in Gyzmo's code, it is initialized at the first call to getInstance. If your singleton class relies on some other subsytem to be initialized, you probably are not doing things in the best way.


Mike
 User Rating: 1022   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message Nil_z    Member since: 1/17/2001  From: Japan
 Posted - 7/23/2001 8:14:17 PM
I am not quite clear about singleton class, maybe someone here will kindly answer my question. Since I want the class to have only one instance, why can't I declare all those member parameters that need to be unique as static member? Can't that do the same job as "singleton class"? Is there any difference between the two?

Thanks a lot.
 User Rating: 1015   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message Vetinari  Moderator Emeritus  Member since: 1/22/2000  From: USA
 Posted - 7/23/2001 9:14:27 PM
quote:
Original post by Nil_z
I am not quite clear about singleton class, maybe someone here will kindly answer my question. Since I want the class to have only one instance, why can't I declare all those member parameters that need to be unique as static member? Can't that do the same job as "singleton class"? Is there any difference between the two?

Thanks a lot.

The best way to implement a singleton class will guarentee that there can not be more than one instance of a class no matter how incompetant the users of the API may be. It will also be initialized lazily so that it is only initialized if it is used. Gyzmo's code above is the best way I know to implement a singleton.


Mike
 User Rating: 1022   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message lonestarr    Member since: 11/19/2002  From: France
 Posted - 11/19/2002 12:31:12 PM
Hi,

there is a bug in CTextureManager::LoadBitmapFile :

pImage = new UBYTE [BitmapInfoHeader.biSizeImage];

should be replaced by :

DWORD trueSize = BitmapInfoHeader.biSizeImage;
if (trueSize==0)
trueSize = BitmapInfoHeader.biWidth * BitmapInfoHeader.biHeight * 3;

pImage = new UBYTE [trueSize];

Just because in MSDN: biSizeImage = Specifies the size, in bytes, of the image. This may be set to zero for BI_RGB bitmaps.

-lonestarr
 User Rating: 1015   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message lonestarr    Member since: 11/19/2002  From: France
 Posted - 11/19/2002 12:37:07 PM
I forgot :
you should also replace any further BitmapInfoHeader.biSizeImage by trueSize

-lonestarr
 User Rating: 1015   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message Cybrid    Member since: 6/21/2005  From: Bilbao, Spain
 Posted - 11/1/2005 2:47:58 PM
Well, I supouse I'm posting a bit late ^_^ , but what if I have another classes to handle the way to obtain data from texture files?. I'm using FreeImage to do it. So at first I have created an abstract class and a set of sub-classes to handle each type of texture file (png,jpg,bmp). Would it be ok if I just instantiate png class in the textureManager class?, or is it impossible due to singleton structure?.

Thanks in advance (if someone replies ;) )
 User Rating: 1015   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message shurcool    Member since: 5/6/2001  From: Toronto, Canada
 Posted - 11/24/2008 1:21:07 PM
There's a minor bug/inconsistency in the DESTROY_TEXMANAGER call. I don't think it's very important because GL textures should get cleaned up anyway when you destroy the GL context, but...

In the header file it mentions the following.
Quote:
To 'clean up' just call DESTROY_TEXMANAGER, this will delete the TexID array and call FreeAll.

But DESTROY_TEXMANAGER doesn't actually call FreeAll like it says.

To fix it, insert one line in the CTextureManager::Destroy() function.
void CTextureManager::Destroy (void) {
	if (m_Singleton) {
		m_Singleton->FreeAll();		// <-- This line was missing

		delete [] m_Singleton->nTexIDs;
		m_Singleton->nTexIDs = 0;
	
		delete m_Singleton;
		m_Singleton = 0;
	}
}
 User Rating: 1137   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message smr  GDNet+  Member since: 7/16/2004  From: Pekin, IL, United States
 Posted - 11/24/2008 2:25:52 PM
I recommend that you forget the singleton and implement this as a normal class. You can then pass the manager object to the constructor of any classes who need it, that way their dependency on the texture manager is clearly and explicitly documented.
 User Rating: 1506   |  Rate This User  Send Private MessageView ProfileView Journal Report this Post to a Moderator | Link

Reply Quoting This MessageEdit Message shurcool    Member since: 5/6/2001  From: Toronto, Canada
 Posted - 11/24/2008 4:08:22 PM
You certainly have a point there. That's exactly how I would do it if I were to do this from scratch today. But don't forget this article is 7 years old. ;) Singletons were something exotic and poorly understood, and hence a FOTM design pattern at the time.
 User Rating: 1137   |  Rate This User  Send Private MessageView Profile Report this Post to a Moderator | Link

All times are ET (US)

Post Reply		  Last Thread Next Thread 
Forum Rules:
You may not post new threads
You may post replies
You may not edit your posts
You may not use HTML in your posts
Jump To:
Administrative Options: