Question

After transferring a large image from a REST endpoint, I need to divide the image into a number of smaller image tiles.

The initial image is (for instance) 1024×1024, stored in an NSData; I need to create sub-image of size 256×256 (In this case, there will be 16 sub-images).

How would this be done? (I haven’t found any articles which even come close, but I assume it must be possible since most image editing software supports image cropping.)

Thanks.

Answer 1

@interface UIImage (Sprite)
- (NSArray *)spritesWithSpriteSheetImage:(UIImage *)image spriteSize:(CGSize)size;
- (NSArray *)spritesWithSpriteSheetImage:(UIImage *)image inRange:(NSRange)range spriteSize:(CGSize)size;
@end




@implementation UIImage (Sprite)

-(NSArray *)spritesWithSpriteSheetImage:(UIImage *)image spriteSize:(CGSize)size {
    return [self spritesWithSpriteSheetImage:self inRange:NSMakeRange(0, lroundf(MAXFLOAT)) 
                              spriteSize:size];
}
-(NSArray *)spritesWithSpriteSheetImage:(UIImage *)image 
                            inRange:(NSRange)range 
                         spriteSize:(CGSize)size {
if (!image || CGSizeEqualToSize(size, CGSizeZero) || range.length == 0) 
    return nil;
NSLog(@"%i %i", range.location, range.length);
CGImageRef spriteSheet = [image CGImage];
NSMutableArray *tempArray = [[[NSMutableArray alloc] init] autorelease];

int width = CGImageGetWidth(spriteSheet);
int height = CGImageGetHeight(spriteSheet);

int maxI = width / size.width;
int startI = 0;
int startJ = 0;
int length = 0;
int startPosition = range.location;

// Extracting initial I & J values from range info
//
if (startPosition != 0) {
    for (int k=1; k<=maxI; k++) {
        int d = k * maxI;
        if (d/startPosition == 1) {
            startI = maxI - (d % startPosition);
            break;
        }
        else if (d/startPosition > 1) {
            startI = startPosition;
            break;
        }
        startJ++;
    }
}
int positionX = startI * size.width;
int positionY = startJ * size.height;
BOOL isReady = NO;
while (positionY < height) {
    while (positionX < width) {
        CGImageRef sprite = CGImageCreateWithImageInRect(spriteSheet, CGRectMake(positionX, positionY, size.width, size.height));
        [tempArray addObject:[UIImage imageWithCGImage:sprite]];
        CGImageRelease(sprite);
        length++;
        if (length == range.length) {
            isReady = YES;
            break;
        }
        positionX += size.width;
    }
    if (isReady) 
        break;
    positionX = 0;
    positionY += size.height;
}
return [NSArray arrayWithArray:tempArray];
  }
@end