A Tasty Pixel » Geekspeak

Links for February 25th through May 29th

Links for February 25th through May 29th:

Implementing iBooks page curling using a conical deformation algorithm Excellent summary of how to implement a convincing page turn animation in OpenGL
Multiplottr.com — Plot, save and share multiple locations on your own customized maps. Batch plot multiple addresses
gmaps.kaeding.name :: Plot multiple locations on Google Maps Enter addresses, one per line, to plot all entries on a map at once
Free iPhone App Marketing — Online and iPhone Marketing Includes a useful list of review sites, blogs, etc.

OS X service to filter selected text through a shell command

The UNIX shell provides a host of extremely useful utilities for modifying text. This OS X Automator service makes all of them available for filtering text in all OS X applications.

This can be handy for performing quick operations, like replacing text with regular expressions, sorting lists or swapping fields around.

When triggered, the service requests a command to use for filtering, then runs the command and replaces the selected text with the result.

Some sample operations:

Sort lines alphabetically/numerically: sort or sort -n
Change to lowercase: tr "[:upper:]" "[:lower:]"
Replace a spelling mistake, taking care of case: sed -E 's/([tT])eh/\1he/g'
Re-order elements in a tab- or comma-separated list: awk '{print $2 $1}' or awk -F, '{print $2 "," $1}'

Put it in Library/Services, and it should appear in the ‘Services’ menu.

Filter through Shell Command.zip

Part 2

[Talkie](http://atastypixel.com/products/talkie) is my newest product, a Walkie Talkie for iPhone and Mac.

In [Part 1](http://atastypixel.com/2010/03/11/the-making-of-talkie-broadcasting/) of this series, I wrote about basic broadcasting. This works fine with one network device, but it’s worth discussing how to send through all devices, so you can communicate with others connected via, say, Ethernet and WiFi simultaneously.

So, in Part 2 I’ll write about the approach I took in Talkie for broadcasting from all network devices (a.k.a. network interfaces), so that one can communicate with others connected via WiFi, Ethernet (on a Mac), and any other network devices simultaneously.

Browsing Core Data databases using F-Script

[F-Script](http://www.fscript.org/), the Cocoa-based scripting environment, now provides some great tools for exploring Core Data databases.

I couldn’t figure out how to easily open up my databases, other than manually creating a managed object model, then a persistent store coordinator, then a managed object context on the console. I couldn’t find any existing tools, and I wanted a quick workflow for opening up my databases, so I put together a script that prompts for the application bundle or .xcdatamodel(d) data model file, then prompts for the XML (.xml), binary (.binary) or SQLite (.sql or anything else) database file, and opens up the inspector.

I wrote it as an Applescript that just calls upon F-Script to evaluate the script, and saved it in an application bundle so I can pull it up quickly.

Here it is:

Core Data Browser.app

It just needs the F-Script app to be available.

Upon opening, the managed object context is available on the console as “context“. So, aside from using F-Script’s object browser, you can also do things like:

> request := (NSFetchRequest alloc) init
> request setEntity:(NSEntityDescription entityForName:'MyEntity' inManagedObjectContext:context)
> request setPredicate:(NSPredicate predicateWithFormat:'type = 3')
> result := context executeFetchRequest:request error:nil
> result
_PFArray {<nsmanagedobject: 0x2006cf740> (entity: MyEntity; id: 0x20064c9e0 <x -coredata://BAC82A67-CC41-48C2-8A96-693B67A501D6/MyEntity/p1> ; data: <fault>), 
<nsmanagedobject: 0x2006bdc80> (entity: MyEntity; id: 0x20064c9c0 <x -coredata://BAC82A67-CC41-48C2-8A96-693B67A501D6/MyEntity/p2> ; data: <fault>), 
<nsmanagedobject: 0x2006bc680> (entity: MyEntity; id: 0x200651180 <x -coredata://BAC82A67-CC41-48C2-8A96-693B67A501D6/MyEntity/p3> ; data: <fault>)
...
</fault></x></nsmanagedobject:></fault></x></nsmanagedobject:></fault></x></nsmanagedobject:>

Update: Now has better error reporting, and the option to load classes from a bundle.

For those interested, here’s the original F-Script:

Easy rounded corners on UITableViewCell image view

Here’s a relatively easy way to achieve rounded corners on the standard image view in a UITableViewCell:

cell.imageView.layer.masksToBounds = YES;
cell.imageView.layer.cornerRadius = 5.0;

Set this up when you create the cell (make sure you #import <QuartzCore/QuartzCore.h> at the top, of course). It would appear the UIImageView control creates sublayers to display the actual image content, which is why we use the masksToBounds property to then clip any sublayers.

I noticed a lot of people are seeking answers to the silly behaviour of UITableView with the grouped (UITableViewStyleGrouped) style and images:

Images don’t get clipped to the rounded cell border, which looks nasty. This technique is one way to remedy that:

One caveat – due to the inexplicable way the image view within the table view cell scales image content, there’s not really a simple, sensible way to provide an inset margin from the table view cell boundary to complement this rounded border effect.

I tried setting the frame property of the UIImageView itself (cell.imageView.frame), as well as setting the frame of the image view’s layer. I also tried applying a scale transform to the layer, with strangely inconsistent results: Setting scale to, say, 50%, made the image view 40x40px, only a pixel or two smaller than the full size. This may be because another entity (the table view cell?) performs scaling of the content, instead of the actual image view; given that my original image was 80×80, a 50% scale would result in 40×40.

My solution was to steer clear of that nonsense and just provide appropriately scaled images straight to the image view. Here’s a simple category on UIImage to scale an image:

@interface UIImage (TPAdditions)
- (UIImage*)imageScaledToSize:(CGSize)size;
@end
 
@implementation UIImage (TPAdditions)
- (UIImage*)imageScaledToSize:(CGSize)size {
    UIGraphicsBeginImageContext(size);
    [self drawInRect:CGRectMake(0, 0, size.width, size.height)];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}
@end

So, then I just do something like this in the UITableView data provider:

UIImage *image = account.image;
if ( image ) {
   cell.image = [image imageScaledToSize:CGSizeMake(38, 38)];
}

Sorted.

Part 1

[Talkie](http://atastypixel.com/products/talkie) is my newest product, the result of a collaboration with a good designer friend, Tim Churchward, who did the user interface.

Talkie is a little different from many of the other walkie talkie applications on the App Store (aside from the fact that much of it was written by me from our motorhome in [Tunisia](http://michael.tyson.id.au/2010/01/26/down-time-in-hammamet/)!), and I thought I’d write a little about some of the tech underpinning the app, and some of the choices we made. Along the way it may get a little tutorial-esque.

This first part will introduce our initial motivations, and will talk about basic broadcast communications — the broadcast communications part may be very familiar to some, in which case it may be worth skipping to the next instalment.
In the [second part](http://atastypixel.com/the-making-of-talkie-broadcasting/), I’ll continue the theme of networking, and will talk about what I ended up with for Talkie’s network code after addressing a couple of things, including switching to multicast.
Finally, I’ll talk audio, dual platform development, and anything else I think of along the way (Actually, I’m aching to talk about one particular upcoming feature that had me jumping up and down when I first thought of it, but for now, mum’s the word on that one.)

Searching through Subversion history

Occasionally I need to search back through old versions of projects to find a piece of code I want to resurrect or just use as reference — I haven’t found any easy built-in way to do this, so I adapted [this useful script](http://svn.haxx.se/users/archive-2006-09/1062.shtml) to allow me to grep through all history from within a Subversion working directory, like:

$ svngrep SecItemCopyMatching *
LSAddAccountController.m @r7: SecItemCopyMatching((CFDictionaryRef)[NSDictionary dictionaryWithObjectsAndKeys:
LSAddAccountController.m @r4: SecItemCopyMatching((CFDictionaryRef)[NSDictionary dictionaryWithObjectsAndKeys:
LSAddAccountController.m @r2: SecItemCopyMatching((CFDictionaryRef)[NSDictionary dictionaryWithObjectsAndKeys:
LSAddAccountController.m @r1: SecItemCopyMatching((CFDictionaryRef)[NSDictionary dictionaryWithObjectsAndKeys:

Here’s the script:

#!/bin/sh
pattern=$1
shift
 
for file in $@; 
do
  svn log -q "$file" 2>/dev/null | perl -ne 'print "$1\n" if /^r(\d+)/' | 
  while read r 
  do
    match=`svn cat -r $r "$file" | grep "$pattern"`
    result=$?
    if [ $result -eq 0 ]
    then
      /bin/echo -n "$file @r$r: "
      /bin/echo $match;
    elif [ $result -ne 1 ]
    then
      exit 2
    fi
  done
done;

Using custom DNS servers from the iPhone and over Internet Tethering

For those of us the roam around on network connections, [OpenDNS](http://www.opendns.com) and [Google Public DNS](http://code.google.com/speed/public-dns/) provide public DNS servers which offer better security than using arbitrary DNS that’s assigned to us when we connect to a network. This means that rather than trusting the assigned DNS server — which could be a malicious third party that’s attempting a man-in-the-middle attack — we always use a trusted server.

In OS X, normally, one can specify custom DNS servers in Network Preferences, but when using Internet Tethering with the iPhone, no options are available.

It’s possible to set DNS configuration on the command line, though, as mentioned in [this MacOSXHints article](http://www.macosxhints.com/article.php?story=20050621051643993).

This technique can be used within a [shell script](http://stackoverflow.org/wiki/Set_the_DNS_server_under_OS_X) to make things easier.

As it happens, if you have a jailbroken iPhone, the trick works there too — just ssh in as root, copy the script over, and run it from the iPhone.

The one caveat is that the DHCP client both on the iPhone and on Mac OS X will routinely reset the servers — I haven’t found a way to combat this yet, other than routinely re-running the script.

We have been using mobile broadband from my iPhone while we’ve been [travelling](http://michael.tyson.id.au/about); our current [provider](http://michael.tyson.id.au/dk2oa) seems to go offline almost every evening — a quirk which I’ve just discovered is related to their faulty DNS server.

Using Google’s public DNS servers instead fixes this problem, so I was after a way to configure both the iPhone and OS X to use the servers.

Geekspeak