この関数は黒の画像を返します。Sparrow Library を使用しています。
これは私のコードです:
-(UIImage *) saveRectangle:(SPRectangle*)rectangle
{
int numberOfComponents = 8;
int width = rectangle.width;
int height = rectangle.height;
NSInteger bufferLenght = width * height * numberOfComponents;
NSMutableData * buffer= [NSMutableData dataWithLength:bufferLenght];
glPixelStorei(GL_PACK_ALIGNMENT, 4); // force 4 byte alignment
glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, [buffer mutableBytes]);
CGDataProviderRef ref = CGDataProviderCreateWithData(NULL, [buffer mutableBytes], bufferLenght, NULL);
CGImageRef iref = CGImageCreate(width, height, 8, 32, width * 4, CGColorSpaceCreateDeviceRGB(), kCGBitmapByteOrderDefault, ref, NULL, true, kCGRenderingIntentDefault);
uint32_t* pixels = (uint32_t *)malloc(bufferLenght);
CGContextRef context = CGBitmapContextCreate(pixels, width, height, 8, width*4, CGImageGetColorSpace(iref), kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrder32Big);
CGContextTranslateCTM(context, 0.0, height);
CGContextScaleCTM(context, 1.0, -1.0);
CGContextDrawImage(context, CGRectMake(0.0, 0.0, width, height), iref);
CGImageRef outputRef = CGBitmapContextCreateImage(context);
free(pixels);
return [UIImage imageWithCGImage:outputRef];
}