wwrob - Developer IT

Cracking the Playfair cipher

- by wwrob

I have the ciphertext and an encrypting program (with the key hardcoded in). How would I go about finding the key? Surely the availability of the encryptor must open up possibilities beyond brute-forcing it.

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Editing an UIImage

- by wwrob

I have an UIImage that I want to edit (say, make every second row of pixels black). Now I am aware of the functions that extract PNG or JPEG data from the image, but that's raw data and I have no idea how the png/jpeg files work. Is there a way I can extract the colour data from each pixel into an array? And then make a new UIImage using the data from the array?

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Drawing single pixel in Quartz

- by wwrob

I have an array of CGPoints, and I'd like to fill the whole screen with colours, the colour of each pixel depending on the total distance to each of the points in the array. The natural way to do this is to, for each pixel, compute the total distance, and turn that into a colour. Questions follow: 1) How can I colour a single pixel in Quartz? I've been thinking of making 1 by 1 rectangles. 2) Are there better, more efficient ways to achieve this effect?

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Basic drawing with Quartz 2D on iPhone

- by wwrob

My goal is to make a program that will draw points whenever the screen is touched. This is what I have so far: The header file: #import <UIKit/UIKit.h> @interface ElSimView : UIView { CGPoint firstTouch; CGPoint lastTouch; UIColor *pointColor; CGRect *points; int npoints; } @property CGPoint firstTouch; @property CGPoint lastTouch; @property (nonatomic, retain) UIColor *pointColor; @property CGRect *points; @property int npoints; @end The implementation file: //@synths etc. - (id)initWithFrame:(CGRect)frame { return self; } - (id)initWithCoder:(NSCoder *)coder { if(self = [super initWithCoder:coder]) { self.npoints = 0; } return self; } - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { UITouch *touch = [touches anyObject]; firstTouch = [touch locationInView:self]; lastTouch = [touch locationInView:self]; } - (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event { UITouch *touch = [touches anyObject]; lastTouch = [touch locationInView:self]; points = (CGRect *)malloc(sizeof(CGRect) * ++npoints); points[npoints-1] = CGRectMake(lastTouch.x-15, lastTouch.y-15,30,30); [self setNeedsDisplay]; } - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { UITouch *touch = [touches anyObject]; lastTouch = [touch locationInView:self]; [self setNeedsDisplay]; } - (void)drawRect:(CGRect)rect { CGContextRef context = UIGraphicsGetCurrentContext(); CGContextSetLineWidth(context, 2.0); CGContextSetStrokeColorWithColor(context, [UIColor blackColor].CGColor); CGContextSetFillColorWithColor(context, pointColor.CGColor); for(int i=0; i<npoints; i++) CGContextAddEllipseInRect(context, points[i]); CGContextDrawPath(context, kCGPathFillStroke); } - (void)dealloc { free(points); [super dealloc]; } @end When I load this and click some points, it draws the first points normally, then then next points are drawn along with random ellipses (not even circles). Also I have another question: When is exactly drawRect executed?

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[bash] checking wget's return value [if]

- by wwrob

I'm writing a script to download a bunch of files, and I want it to inform when a particular file doesn't exist. r=`wget -q www.someurl.com` if [ $r -ne 0 ] then echo "Not there" else echo "OK" fi But it gives the following error on execution: ./file: line 2: [: -ne: unary operator expected What's wrong?

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[sed] Multiline trimming

- by wwrob

I have a html file that I want to trim. I want to remove a section from the beginning all the way to a given string, and from another string to the end. How do I do that, preferably using sed?

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Why should I use floats?

- by wwrob

I mean, for pixel position, sizes, etc. It's not like I'll be making a rectangle that's 100 and a half pixels high. These might as well be integers.

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Xcode - change project templates

- by wwrob

So I can add new templates for single files, but I want Xcode to uses these files when setting up the new project (most noticeably the Controller and Delegate .h and .m files). How do I do that?

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Understanding prolog [lists]

- by wwrob

I am to write a program that does this: ?- pLeap(2,5,X,Y). X = 2, Y = 3 ; X = 3, Y = 4 ; X = 4, Y = 5 ; X = 5, Y = 5 ; false. (gives all pairs X,X+1 between 2 and 5, plus the special case at the end). This is supposedly the solution. I don't really understand how it works, could anyone guide me through it? pLeap(X,X,X,X). pLeap(L,H,X,Y) :- L<H, X is L, Y is X+1. pLeap(L,H,X,Y) :- L=<H, L1 is L+1, pLeap(L1,H,X,Y). I'd do it simply like this: pLeap(L,H,X,Y) :- X >= L, X =< H, Y is X+1. Why doesn't it work (ignoring the special case at the end)?

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Point-free in Haskell

- by wwrob

I have this code that I want to make point-free; (\k t -> chr $ a + flip mod 26 (ord k + ord t -2*a)) How do I do that? Also are there some general rules for point free style other than "think about this amd come up with something"?

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[multiple issues] Customizing Xcode [fonts, code sense, and more]

- by wwrob

How can I make code completion case-sensitive? How can I make Ctrl-k kill the content of the line and the new line character? How can I make backspace always delete only one character, no matter what it is? Right now, it deletes spaces in chunks equal to my indent level. How to change the indentation style in file templates? I like to have the opening brace on its own line. How can I make the font aliased? EDIT: Issues 4 and 5 are solved. 1 through 3 are still open.

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