Loading images into OpenGL in iPhone

Mar

Loading images into OpenGL in iPhone

So you can’t make a game without images, right? Well, actually you can but that’s another story.

But how can you load a jpg or a png and use then on OpenGLES?

First let’s make a simple class Texture2D

class Texture2D 
{
public:
	Texture2D(int texture id, int width, int height)
        {
           _textureId = id; _width = width; _height = height;
        }
 
	virtual ~Texture2D(void)
        {
             // Delete Texture from HGL Memory
             glDeleteTextures(1, ((GLuint*)&_textureId));
        }
	int  getTextureId() {return _textureId; }
protected:
	int _textureId;   // The reference ID of the texture in OpenGL memory
        int _width;
        int _height;
};

Now for the code to actually load the image

Texture2D* IPhoneOperativeSystem::LoadImage(std::string imagefile)
{
         // Id for texture
	GLuint texture;	
        // Generate textures
	glGenTextures(1, &texture); 
	// Bind it
	glBindTexture(GL_TEXTURE_2D, texture);
	// Set a few parameters to handle drawing the image at lower and higher sizes than original
	glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR); 
        glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE);
 
 
	NSString *path = [[NSString alloc] initWithUTF8String:imagefile.c_str()];
 
         NSData *texData = [[NSData alloc] initWithContentsOfFile:path];
        UIImage *image = [[UIImage alloc] initWithData:texData];
        if (image == nil)
	  return NULL;	
        // Get Image size
       GLuint width = CGImageGetWidth(image.CGImage);
       GLuint height = CGImageGetHeight(image.CGImage);
       CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
       // Allocate memory for image
       void *imageData = malloc( height * width * 4 );
       CGContextRef imgcontext = CGBitmapContextCreate( imageData, width, height, 8, 4 * width, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big );
       CGColorSpaceRelease( colorSpace );
       CGContextClearRect( imgcontext, CGRectMake( 0, 0, width, height ) );
       CGContextTranslateCTM( imgcontext, 0, height - height );
       CGContextDrawImage( imgcontext, CGRectMake( 0, 0, width, height ), image.CGImage );
 
        // Generate texture in opengl
       glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, imageData);
	// Release context
	CGContextRelease(imgcontext);
	// Free Stuff
        free(imageData);
       [image release];
       [texData release];
 
       // Create and return texture
       Texture2D* tex = new Texture2D(texture,width, height);
       return tex;
}

So right now you can do something like

   Texture2D* tree_image = IPhoneOperativeSystem("tree_image.jpg");

For drawing, before sending your primitives just do something like:

glBindTexture(GL_TEXTURE_2D, tree_image->getTextureId());

This code should work on all iOS devices

Tags: iphonedev, opengl

Posted by David Amador under Game Development
You can leave a response, or trackback from your own site.

Andreas Panos Says:
March 18th, 2011 at 12:47

May I suggest a small correction :

you need to set the buffer to 0 after the malloc
memset(imageData,0,(height * width * 4 ));

David Amador Says:
March 18th, 2011 at 12:50

Thanks, although it’s not necessary to do it since the imageData is going to be fully written it’s always a good practice to memset it =)

Miguel A. Friginal Says:
March 18th, 2011 at 15:34

I would not malloc+memset. If you really need to zero out memory (in this case, as you say, you don’t!) use calloc. This is from the Memory Usage Performance Guide from Apple:

When you call memset right after malloc, the virtual memory system must map the corresponding pages into memory in order to zero-initialize them. This operation can be very expensive and wasteful, especially if you do not use the pages right away

The calloc routine reserves the required virtual address space for the memory but waits until the memory is actually used before initializing it. This approach alleviates the need to map the pages into memory right away. It also lets the system initialize pages as they’re used, as opposed to all at once.

38leinaD Says:
March 19th, 2011 at 12:41

There is a standard objective-c class published from Apple called Texture2D doing the exact same task (an more). Maybe also have a look at that one. Should be easy to change it from obj-c to c++.

cheers

David Amador Says:
March 19th, 2011 at 12:44

Thanks for the tip, I kept using my own because of portability for all my games

Michael Adaixo Says:
March 21st, 2011 at 14:14

This came at the right time.
Thank you

Diogo de Andrade Says:
March 30th, 2011 at 16:58

Right timming indeed… But I’m having an issue with this…

I’ve added a .png file (test.png) to the resources, and made sure it gets copied to the output (it’s under Copy Bundle Resources on xCode)…

Then I debug and when I reach the

NSData *texData = [[NSData alloc] initWithContentsOfFile:path];

path has the correct value (“test.png”), but the texData is empty after it runs this line… I went into the “build\Debug-iphoneos\unidir_vod_test.app” directory, and the “test.png” file is there (so I’m guessing it reaches the iPad)…

I’m wondering if I’m missing any permissions, or if the filepath is not correct (maybe something gets introduced by the system when it builds the local filesystem)…

Tried a websearch, but it’s like needle in a haystack… :\

Any ideas?

David Amador Says:
March 30th, 2011 at 17:09

Each iOS app has a specific container where it runs and stores his files.

To access the resourcePath you must query the mainBundle like this:

NSString *path = [[NSBundle mainBundle] resourcePath];

Now lets assume you place everything inside a folder called “Game_Resources”.

NSString *path = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"Game_Resources"];

To get a std::string just do

std::string path = [path UTF8String];

Hope it helps

Diogo de Andrade Says:
March 30th, 2011 at 17:59

It helped… took me a while to understand “resourcePath” on the first line was the method of the class and not a variable…

It’s working now (I think, haven’t done anything with the texture yet), so thanks a million…

Some additional questions:

1) Do I have to release the NSString *path I got from NSBundle (or is it just a reference)?
2) Why use “stringByAppendingPathComponent”, instead of just adding “/Game_Resources” to the resulting std::string?
3) How do I say to my resources to go a specific directory, instead of being in the root directory of my application?

Again, thanks for the help, this is confusing for an “old-school” PC/C++ programmer… and don’t get me started with getting the certificates up and running!

David Amador Says:
March 30th, 2011 at 18:31

1) You should release it yes [path release];
2) It’s just for convenience. Older iOS sdk would return without the end / others with. This way you don’t have to bother with that. If you have some kind of folder structure inside you can append it the regular way.
3) The best way is to place everything inside a folder on your project root, let’s call it game_assets. Add that folder to your XCode project inside Resources. But when adding it use “folder references” as an option. The folder should be blue and replicate your structure even if you change it outside Xcode.