Flood fill Crash - objective-c

Question

I have been trying to get a simple Flood Fill Algorithm working for an iPhone app that I am developing and I just can't get it working correctly.
I have got the actual process to work great however the app will crash when the fill is too large. From what I can tell its because the thread is overflowing from all of the functions running. From what I have read, I need to implement a stack but I can't work out how this works.
typedef struct {
int red;
int green;
int blue;
} color;
#interface EMFloodTest : UIViewController {
UIImageView *mainImage;
unsigned char *imageData;
color selColor;
color newColor;
int maxByte;
}
#end
#implementation EMFloodTest
- (void)setupImageData {
CGImageRef imageRef = mainImage.image.CGImage;
if (imageRef == NULL) { return; }
NSUInteger width = CGImageGetWidth(imageRef);
NSUInteger height = CGImageGetHeight(imageRef);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;
maxByte = height * width * 4;
imageData = malloc(height * width * 4);
CGContextRef context = CGBitmapContextCreate(imageData, width, height, bitsPerComponent, bytesPerRow, colorSpace,
kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);
CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
CGContextRelease(context);
}
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
if (self) {
mainImage = [[UIImageView alloc]initWithImage:[UIImage imageNamed:#"Color6.png"]];
[self.view addSubview:mainImage];
newColor.red = 255;
newColor.green = 94;
newColor.blue = 0;
[self setupImageData];
}
return self;
}
- (void)updateImage {
CGImageRef imageRef = mainImage.image.CGImage;
if (imageRef == NULL) { return; }
NSUInteger width = CGImageGetWidth(imageRef);
NSUInteger height = CGImageGetHeight(imageRef);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;
CGContextRef context = CGBitmapContextCreate(imageData, width, height, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast );
imageRef = CGBitmapContextCreateImage (context);
mainImage.image = [UIImage imageWithCGImage:imageRef];
CGContextRelease(context);
}
- (void)setPixel:(NSUInteger)byte toColor:(color)color {
imageData[byte] = color.red;
imageData[byte+1] = color.green;
imageData[byte+2] = color.blue;
}
- (BOOL)testByte:(NSInteger)byte againstColor:(color)color {
if (imageData[byte] == color.red && imageData[byte+1] == color.green && imageData[byte+2] == color.blue) {
return YES;
} else {
return NO;
}
}
// This is where the flood fill starts. Its a basic implementation but crashes when filling large sections.
- (void)floodFillFrom:(NSInteger)byte bytesPerRow:(NSInteger)bpr {
int u = byte - bpr;
int r = byte + 4;
int d = byte + bpr;
int l = byte - 4;
if ([self testByte:u againstColor:selColor]) {
[self setPixel:u toColor:newColor];
[self floodFillFrom:u bytesPerRow:bpr];
}
if ([self testByte:r againstColor:selColor]) {
[self setPixel:r toColor:newColor];
[self floodFillFrom:r bytesPerRow:bpr];
}
if ([self testByte:d againstColor:selColor]) {
[self setPixel:d toColor:newColor];
[self floodFillFrom:d bytesPerRow:bpr];
}
if ([self testByte:l againstColor:selColor]) {
[self setPixel:l toColor:newColor];
[self floodFillFrom:l bytesPerRow:bpr];
}
}
- (void)startFillFrom:(NSInteger)byte bytesPerRow:(NSInteger)bpr {
if (imageData[byte] == 0 && imageData[byte+1] == 0 && imageData[byte+2] == 0) {
NSLog(#"Black Selected");
return;
} else if ([self testByte:byte againstColor:newColor]) {
NSLog(#"Same Fill Color");
} else {
// code goes here
NSLog(#"Color to be replaced");
[self floodFrom:byte bytesPerRow:bpr];
[self updateImage];
}
}
- (void)selectedColor:(CGPoint)point {
CGImageRef imageRef = mainImage.image.CGImage;
if (imageRef == NULL) { return; }
if (imageData == NULL) { return; }
NSInteger width = CGImageGetWidth(imageRef);
NSInteger byteNumber = 4*((width*round(point.y))+round(point.x));
NSInteger bytesPerPixel = 4;
NSInteger bytesPerRow = bytesPerPixel * width;
selColor.red = imageData[byteNumber];
selColor.green = imageData[byteNumber + 1];
selColor.blue = imageData[byteNumber + 2];
NSLog(#"Selected Color, RGB: %i, %i, %i",selColor.red, selColor.green, selColor.blue);
NSLog(#"Byte:%i",byteNumber);
[self startFillFrom:byteNumber bytesPerRow:bytesPerRow];
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [touches anyObject];
CGPoint location = [touch locationInView:mainImage];
[self selectedColor:location];
}
Any help on how I might be able to implement a stack or even use another algorithm would be greatly appreciated.
Best,
Darren

Answer 1

The problem is recursive implementation.
Too much deep recursive call to function make stack overflow error.
You have to implement your algorithm in iterative manner.
If you want to see iterative example of flood Fill you can visit:
UIImageScanlineFloodfill