When I load a texture as RGBA4444 in openGL, how much memory is consumed in the device?

How much memory will consume a texture loaded with this method ?

With this method, will a 1024x1024 texture consume 4MB anyway ? ( regardless of loading it as RGBA4444 ) ?

-(void)loadTexture:(NSString*)nombre {
CGImageRef textureImage     =[UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:nombre ofType:nil]].CGImage; 
if (textureImage == nil) {
    NSLog(@"Failed to load texture image");
    return;
}


// Dimensiones de nuestra imagen
imageSizeX= CGImageGetWidth(textureImage);
imageSizeY= CGImageGetHeight(textureImage);

textureWidth = NextPowerOfTwo(imageSizeX);  
textureHeight = NextPowerOfTwo(imageSizeY);


GLubyte *textureData = (GLubyte *)calloc(1,textureWidth * textureHeight * 4);

CGContextRef textureContext = CGBitmapContextCreate(textureData, textureWidth,textureHeight,8, textureWidth * 4,CGImageGetColorSpace(textureImage),kCGImageAlphaPremultipliedLast );
CGContextDrawImage(textureContext, CGRectMake(0.0, 0.0, (float)textureWidth, (float)textureHeight), textureImage);

/**************** Convert data t开发者_运维百科o RGBA4444******************/   
//Convert "RRRRRRRRRGGGGGGGGBBBBBBBBAAAAAAAA" to "RRRRGGGGBBBBAAAA"
void *tempData = malloc(textureWidth * textureHeight * 2);
unsigned int* inPixel32 = (unsigned int*)textureData;
unsigned short* outPixel16 = (unsigned short*)tempData;
for(int i = 0; i < textureWidth * textureHeight ; ++i, ++inPixel32)
    *outPixel16++ = 
    ((((*inPixel32 >> 0) & 0xFF) >> 4) << 12) | // R
    ((((*inPixel32 >> 8) & 0xFF) >> 4) << 8) | // G
    ((((*inPixel32 >> 16) & 0xFF) >> 4) << 4) | // B
    ((((*inPixel32 >> 24) & 0xFF) >> 4) << 0); // A


free(textureData);
textureData = tempData;

// Ya no necesitamos el bitmap, lo liberamos
CGContextRelease(textureContext);

glGenTextures(1, &textures[0]);

glBindTexture(GL_TEXTURE_2D, textures[0]);

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, textureWidth, textureHeight, 0, GL_RGBA, GL_UNSIGNED_SHORT_4_4_4_4, textureData);

free(textureData);


//glEnable(GL_BLEND);

glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);   

}

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The GL ES 1.1.12 specification (pdf) has this to say on the subject:

The GL stores the resulting texture with internal component resolutions of its own choosing. The allocation of internal component resolution may vary based on any TexImage2D parameter (except target), but the allocation must not be a function of any other state and cannot be changed once established.

However, according to the iphone dev center, RGBA4444 is natively supported. So I would expect it to consume 2MB with your code snippet. Do you have reasons to doubt it's using 2MB ?

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In OpenGL, there is no way to find out how much video-memory a texture uses.

Also there is no single answer to the question to start with. Such details depend on graphic card, driver version, platform..

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From the OpenGL ES Programming Guide for iOS:

If your application cannot use compressed textures, consider using a lower precision pixel format. A texture in RGB565, RGBA5551, or RGBA4444 format uses half the memory of a texture in RGBA8888 format. Use RGBA8888 only when your application needs that level of quality.

Above that paragraph, they also really recommend using PVRTC compressed textures, because they save even more memory.