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Listen to me!
When I am in my office working (and thinking) I am usually listening to music of various kinds from Argentine Tango through to Russian Techno. But when I am working out at the gym I have been listening to a lot of technical/gadget podcasts in order to keep my mind distracted from all the sweaty stuff. So this week I wanted to mention two of my favourite[1] technical podcasts.

Software Engineering Radio
The Software Engineering Radio podcast has been running since 2006, yet I only discovered it this week. Up until January 2012 this was an independent podcast, but since Feburary it has been published under the wings of IEEE Software, itself a magazine published by the IEEE Computer Society. The best way to describe the podcast is to quote from the site itself:

Software Engineering Radio is a podcast targeted at the professional software developer. The goal is to be a lasting educational resource, not a newscast. Every two to four weeks, a new episode is published that covers all topics software engineering. Episodes are either tutorials on a specific topic, or an interview with a well-known expert from the software engineering world.

Since Software Engineering Radio was founded in 2006, it has published over 180 episodes on a wide variety of software engineering topics. SE Radio has evolved into one of the premier software podcasts, and many luminaries and opinion leaders in the field have appeared on the show. In fact, we just reached a huge milestone: over 5 million downloads.

Although that may sound dry, to any software professional the breadth and depth of the topics it covers is simply astonishing. Some recent examples of their episodes include things like:

  • The Mainframe
  • Domain-specific languages
  • Leading Agile Developers
  • Quantum computing
  • Game Development

The series is available on iTunes as well as directly from their website, however each episode on the SE Radio site typically contains additional URLs to sites relevant to that episode.

This week I have managed to listen to the Mainframe episode, and also one going back to 2010 “C++0X with Scott Meyers”. When I was working a lot in C++, Scott was my favourite author, so I was thrilled to listen to him speak on the latest changes to C++ (which due to delays morphed from C++0X into C++11). That episode also brought forth a C++ nerdy joke:

Q. Why doesn’t C++ have garbage collection?
A. Because then there wouldn’t be anything left!

And while I have only listened to two episode, I can’t also say enough about the podcast’s host. While other episodes may have different hosts, in the ones I listed to the host was extremely knowledgable in his own right, and was asking thought-provoking questions that really engaged the guests. And that makes for a great podcast!

In the coming weeks I will be catching up on a lot of previous episode related to Agile and Scrum, but with over 180 episodes to choose from I’m going to have to prioritize my listening!

FLOSS Weekly
The other podcast on my favourite list is Floss Weekly, a podcast that is (to quote):

We’re not talking dentistry here; FLOSS all about Free Libre Open Source Software. Join host Randal Schwartz and his rotating panel of co-hosts every Wednesday as they talk with the most interesting and important people in the Open Source and Free Software community.

This podcast is a great way to get to know various open source initiatives that you may never have heard about before, such as:

  • Autotest software testing framework
  • FreeNAS disk storage solution
  • Tiki Wiki Groupware
  • LinuxMCE home automation
  • VirtualBox software virtualization

Again the series is also available on iTunes.

I have listened to a lot more of these podcasts than SE Radio, and while the FLOSS Weekly ones don’t go into as much depth, they have certainly introduced me to a lot of things that I had never heard of.

One of the episodes that really interested me described the Village Telco project which is a mesh based, wireless, VoIP, local DIY phone solution. I can see this fitting in with some of the volunteer work I am doing for Engineers Without Borders. I would never have even considered this solution with having heard the FLOSS Weekly podcast.

Au revoir
Again, its been wonderful!


[1] Yes I will keep spelling favourite as favourite and screw what Safari says is a spelling error.

NOTE that this code has been updated to support iOS6 and the 4 inch retina screen

The What And Why Of It All
This week I’m giving back some code that I developed as a learning exercise for moving an object along a bezier path under the iOS environment. This code also has its roots in the answers to some questions I posted on, hence part of my desire to give back a fully working solution. These questions being:

iOS CAKeyframeAnimation rotationMode on UIImageView: Solved

iOS CAKeyFrameAnimation Scaling Flickers at animation end


The PathMove program allows the user to set up a predetermined set of bezier paths and then trigger a UIImageView object to move from start to end along that path. The program incorporates several options to do things like:

  • Select the ending quadrant of the bezier path.
  • Mix and match three different predefined bezier path segments for the starting and ending segments of the overall path.
  • Allow the object to grow, shrink or remaiin the same size as it moves along the path.
  • Rotate the object to match the tangent of the bezier curve as the object moves.
  • Pre-Rotate the object by 90 degrees to accommodate how iOS calculates a tangent.
  • Annotate the complete bezier path with the size and location of all of the path’s the control points

You can download the source code for PathMove from GitHub at

I have released this code under a BSD-3 license, so you are free to use however you like as long as you acknowledge where it originated from. And if you do use any part of it please drop me a line to let me know!

Screen Shots

The program consists of two screens – a main screen where the path is drawn and the object moves, and a setup screen which contains all the options that the user can make. The following screen shots show the object moving along a path and the corresponding setup screen that created the path. The final screen shot shows how the bezier path can be annotated in order to show all the control points.

PathMove Main screen

PathMove Main screen

PathMove setup screen

PathMove setup screen

PathMove Annotated Path

PathMove Annotated Path

Code Construction
The PathMove program is built up from the following classes:

  • JdViewController Forms the display for the main screen and animates the object to move along the bezier path.
  • JdGraphicView Draws the graph axis, bezier path and assorted boxes.
  • JdSetupViewController Forms the display for the setup screen.
  • JdConfiguration Passes configuration information between the two screens.
  • JdBezierPoint Contains the definitions of a single bezier point in the path.
  • JdBezierPath Maintains a list of JdBezierPoint definitions and constructs a smooth bezier path from options passed into it.

Notable Points
There are several interesting points about PathMove.

Rather than directly construct a UIBezierPath object, PathMove constructs an array of JdBezierPoint objects, each of which describes a location along the desired bezier path, including the main and control points. This allows you to do nifty things like drawing the locations of the control points on the display, rather than just the actual bezier path. Before I did this I had a hell of a time trying to visualize the bezier path and how changes to the control points affected it. Once I could see the control points on the screen it became so much simpler to say “yep .. just move that control point by X degree and extend it by a little bit more. Short of having a drawing package that allows dragging and dropping control points, this is one of my favorite features of PathMove.

The animations are built up from a combination of CAAffineTransforms and CAKeyframeAnimation animation. Figuring out this combination of transforms and animations gave me the biggest headache and I only really nailed it after I got answers to my StackOverflow questions.

Within the animations, the biggest issue I ran into was the “Rotate the object with the path” option. In the code this is enabled by setting the rotationMode property on the CAKeyframeAnimation object. In Apples documentation for this property CAKeyframeAnimation Class Reference: rotationMode they helpfully say:

Determines whether objects animating along the path rotate to match the path tangent.

You’d think that setting this would mean that the object in question keep its orientation relative to the tangent of the path. Well it does .. sort of. What Apple should have said is:

Determines whether objects animating along the path rotate their horizontal axis to match the path tangent, and that once animation starts the object will be automatically rotated so that its horizontal axis is tangential to the path.

Thus if you want an axis other than the objects horizontal axis to be tangential to the path, you have to pre-rotate the object by the angle between the desired and horizontal axis. This is the reasoning behind the “Pre-Rotate object” option in the Setup screen.

Th’ Th’ That’s all folks
Hope you enjoy this program.


Not happy Jan
While the integration of Git into XCode is a good step forward, for me it doesn’t go far enough. As I have been using XCode and Git I have been finding many use cases which you just can’t do within XCode, and that force you to drop back to the command line in order to get things. This includes things like seeing the true state of things, creating branches from previous commits and helping XCode/Git sort out the state of a project after it got a little confused.

So this week I am going to keep on the subject of Git point out a couple useful command line basics. This won’t be an extensive Git tutorial, so if you are looking for a whole lot more, then you should head on over to somewhere like Top 10 Git Tutorials for Beginners where you’ll find an extensive list of dedicated tutorials.

Before you can use any of these commands, you’ll need to open a Terminal window and navigate to the directory that your project is located in.

So show me!
The most basic Git command you can use is simply:


Which will respond with a summary of all the Git sub-commands

usage: git [--version] [--exec-path[=]] [--html-path]
           [-p|--paginate|--no-pager] [--no-replace-objects]
           [--bare] [--git-dir=] [--work-tree=]
           [-c name=value] [--help]
            <command> [<args>]

The most commonly used git commands are:
   add        Add file contents to the index
   bisect     Find by binary search the change that introduced a bug
   branch     List, create, or delete branches
   checkout   Checkout a branch or paths to the working tree
   clone      Clone a repository into a new directory
   commit     Record changes to the repository
   diff       Show changes between commits, commit and working tree, etc
   fetch      Download objects and refs from another repository
   grep       Print lines matching a pattern
   init       Create an empty git repository or reinitialize an existing one
   log        Show commit logs
   merge      Join two or more development histories together
   mv         Move or rename a file, a directory, or a symlink
   pull       Fetch from and merge with another repository or a local branch
   push       Update remote refs along with associated objects
   rebase     Forward-port local commits to the updated upstream head
   reset      Reset current HEAD to the specified state
   rm         Remove files from the working tree and from the index
   show       Show various types of objects
   status     Show the working tree status
   tag        Create, list, delete or verify a tag object signed with GPG

See 'git help ' for more information on a specific command.

Of these the one I use the most is:

git status

As it shows what the current state of my repository is. For example, on a project I am currently working on, running this command results in:

165-156-000-000:NotchFlow joalah$ git status

# On branch master
# Changes not staged for commit:
#   (use "git add <file>..." to update what will be committed)
#   (use "git checkout -- <file>..." to discard changes in working directory)
#	modified:   NotchFlow/CalcViewController.m
no changes added to commit (use "git add" and/or "git commit -a")

Which tells me that I am working on the “master” branch and there is one file that has been modified but not yet committed to the repository. While I knew from the XCode IDE that I had modified a file, the IDE itself doesn’t tell you what branch you are currently working on. For that you need to either open the XCode Organizer, or drop into the command line.

Another important command for seeing what is what, is:

git branch

By itself it will list out the branches that exist in the repository, and mark the one that is currently checked out:

n165-156-000-000:NotchFlow joalah$ git branch
* master

And finally the ultimate list of information from the repository can be seen in:

git log

This lists everything that has been done, tracking each change with the hash of each commit, and listing them all the way to the creation of the repository. For a project that has been under development for a while this can be a surprisingly long list of commits. Thus the log command comes with a slew of options with which to limit, arrange and order its results. The simplest of these options are things like:

-n Limits the output to the previous ‘n’ commits
-pretty=oneline Summarizes the commit hash and comment all on one line
--abbrev-commit Displays a partial commit hash

An example of using this command is:

n165-156-000-000:NotchFlow joalah$ git log --pretty=oneline -5 --abbrev-commit
adb209e Merged in cleanup of main view controller
55f771a Removed unused file
0624d7c Finished ceasing up locations
705aef0 ignoring autogenerated files
7c03745 Cleaned up location of text

One benefit of the abbreviated commit hash is that you can use it anywhere that git wants to see a commit hash. Thus you don’t have to key in all 40 characters of the full commit hash all the time.

Jumping from branch to branch
Once you know what branches are available, you can easily switch between them with

git checkout <branchname>

For example:

n165-156-000-000:NotchFlow joalah$ git branch
* master

n165-156-000-000:NotchFlow joalah$ git checkout CleanupMVC
M	NotchFlow/CalcViewController.m
Switched to branch 'CleanupMVC'

n165-156-000-000:NotchFlow joalah$ git branch
* CleanupMVC

Splitting branches
Like from within the XCode Organizer tool you can create and delete branches using the git command line. But differing from the Organizer you can also do so with a lot more options than just creating a new branch from the current state of an existing branch. The git command for branching:

git branch

Has some useful variations such as:

-m [<oldbranch>] <newbranch> Move or rename an existing branch.
-d <branchname> Delete an existing branch.
<branchname> [<start-point>] Create a new branch.

To me the ‘Create’ variant is the most useful, as it allows you to create a new branch from an arbitrary starting point in the repository. The starting point can be one of:

<branchname> The name of an existing branch
<commit-id> An arbitrary commit id from anywhere in the repository
<tag> An arbitrary tag from anywhere in the repository

If it is not specified, the the HEAD of the currently checked out branch will be used.

The following is an example of creating a new branch from a pre-existing commit, and then checking out the new branch. Note that the starting point was specified with only the abbreviate commit hash:

n165-156-000-000:NotchFlow joalah$ git log -5 --pretty=oneline -5 --abbrev-commit
55f771a Removed unused file
0624d7c Finished ceasing up locations
7c03745 Cleaned up location of text
e0bb05d Working with new messaging system
e70b543 Back together again .. I think

n165-156-000-000:NotchFlow joalah$ git branch WorkingAgain e0bb05d

n165-156-000-000:NotchFlow joalah$ git branch
* CleanupMVC

n165-156-000-000:NotchFlow joalah$ git checkout WorkingAgain
M	NotchFlow/CalcViewController.m
Switched to branch 'WorkingAgain'

n165-156-000-000:NotchFlow joalah$ git log -5 --pretty=oneline -5 --abbrev-commit
e0bb05d Working with new messaging system
e70b543 Back together again .. I think
2c98537 New Display sort of broken
50b9427 Mostly works
e7d9596 Sort of working with new keyboard
n165-156-000-000:NotchFlow joalah$ 

Marking the trail
Finally in order to indicate a significant milestone in the life of a project, you can mark a commit with a tag. A tag is simply a text string that carries some meaning for the person who created it. Typically you would tag a commit to indicate something like the completion of a specific release version. The tags also include a description part which you can use to explain why a commit has been tagged.

With the git command:

git tag

You can list, add and delete tags through the commands options. Useful combinations of these options are:

-l [-n[<num>]] List all the existing tags, with ‘num’ lines of their descriptions. Note that if not specified, ‘num’ defaults to zero!
<tagname> -m <msg> [<commit>] Create a new tag with a a description <msg> for either the last or an arbitrarily specified commit hash
-d <tagname> Delete a tag

As an example:

n165-156-000-000:NotchFlow joalah$ git tag -l -n1
v0.01           Technical Feature Complete

n165-156-000-000:NotchFlow joalah$ git tag v1.0 -m 'testing tags'

n165-156-000-000:NotchFlow joalah$ git tag -l -n1
v0.01           Technical Feature Complete
v1.0            testing tags

n165-156-000-000:NotchFlow joalah$ git tag -d v1.0
Deleted tag 'v1.0' (was 3e9e48e)

n165-156-000-000:NotchFlow joalah$ git tag -l -n1
v0.01           Technical Feature Complete

Given a git tag, you can see the associate hash from this command:

git show <tag>

By default this produces a rather verbose output, but it can be trimmed down with a format option as in this example:

n165-156-000-000:NotchFlow joalah$ git show V1.0 -s --format="%h, %cd, %cr, %s"
tag v1.0
Tagger: Peter Milway <>

testing tags
e41ee4a, Wed Mar 14 15:51:28 2012 -0400, 68 minutes ago, Added changes

Once again its been a pleasure

Note that I have revised these ideas in Displaying Git details in XCode projects revisited

Cruising along
Source or Version control systems (VCS) are great for organizing the journey of a program from its initial inception through to the latest release. Through judicious use of committing and tagging your files, you can easily retrieve, rebuild or debug any version of code from anywhere in your programs life history. (In fact proper use of a source control system is something that all professional software writers should master, no matter what flavour.)

With XCode 4, Apple chose to integrate Git directly into the editor, allowing it to offer to build repositories each time you create a new project. As a VCS, Git is one of the more modern varieties, built on a premise of distributed software development, and easily creating and merging multiple branches of code in parallel. But while not everyone works with a development team distributed around the world, everyone should know how to create and merge branches in XCode.

The ease of branching in Git helps to keep the main branch of your code pollution free. Instead of trying a new feature in the release version, you branch off the entire codebase to a test branch, and try new things, or build new features in isolation. Then when you are happy with the result, you just merge your changes back into the main branch.

Rocks ahead!
But what if you have multiple versions/branches of your program out in the world and a user reports a bug. How do you know what code was used to build that particular instance? Somehow you need to reconcile the bug report with the code in your VCS, so you know what code to pull for testing. If only the bug report was tagged with the codes version and you could look up that tag in the repository!

A naive way of doing this would be to place a string or numeric constant in your code that described the current version information and then manually update it when you decided on a version change. This could then be displayed on a label somewhere in your program.

NSString* version = @"Version 1.1";


label.text = version;

The problem with this type of system is two-fold:

  1. The version is never guaranteed to be correct, as you will make changes to the program, but forget to update the string.
  2. The VCS doesn’t know about the string, so you can’t ask it to return that particular version

Charting a better course
As the VCS knows about the what versions of code are stored in it, it is better to get the VCS to tell the code what version it is. And if you make this a part of the projects build system, then this will happen automatically and seamlessly – thus saving you from a manual step.

In the case of Git, there are several items that can be extracted from the repository that can uniquely identify what version of code was used to build a particular application’s release:

  • The current branch name
  • The last commit hash
  • The last commit date
  • The last commit comment
  • The last repository tag

All of these items can easily be obtained by running the command line Git tool like so:

Current branch name: git rev-parse –abbrev-ref HEAD
Last commit hash: git log –pretty=format:”%h” -1
Last commit date: git log –pretty=format:”%ad” –date=short -1
Last commit comment: git log –pretty=format:”%s” -1
Last repository tag: git describe –abbrev=0 –tags

(For a description of these commands, please see the Git website)

All that is needed now is to integrate this into your projects build system!

Building the build system
When I researched how to get the Git details into a project, there were several solutions that involved running a script, creating a file and modifying plists and then doing a few more other things. To me they were overcomplicating things a bit. All I wanted was to create a bunch of #defines in a simple .h file and include that where it was needed. Doing this in XCode 4 turned out to be very very easy. All that I did was:

  1. Select the target I want to include the Git data in
  2. Selected the Build Phases of the target
  3. Created a new “Run Script”
  4. Entered OSX shell script commands to create the .h file
  5. Imported the .h file into the source as needed
  6. Added the .h file to my git .ignore file

Visually this is:

Select the Target in the project</td
Go to the Build Phases</td
Create a new “Run Script” phase</td
Move the “Run Script” to be before the “Compile Sources” phase</td
Edit the “Run Script”</td

All is revealed
My script file that I inserted into the Run Scripts is:

# build data file that is included in the source
# so we can automatically report Git repo information
# in the application

buildDate=`date "+%F %H:%M:%S"`
currentBranch=`git rev-parse --abbrev-ref HEAD`
lastCommitHash=`git log --pretty=format:"%h" -1`
lastCommitDate=`git log --pretty=format:"%ad" --date=short -1`
lastCommitComment=`git log --pretty=format:"%s" -1`
lastRepoTag=`git describe --abbrev=0 --tags`

echo -e "//-----------------------------------------" > $gitDataFile
echo -e "// Auto generated file" >> $gitDataFile
echo -e "// Created $buildDate" >> $gitDataFile
echo -e "//-----------------------------------------" >> $gitDataFile
echo -e "" >> $gitDataFile
echo -e "#define BUILD_DATE              @\"$buildDate\"" >> $gitDataFile
echo -e "#define GIT_CURRENT_BRANCH      @\"$currentBranch\"" >> $gitDataFile
echo -e "#define GIT_LAST_COMMIT_HASH    @\"$lastCommitHash\"" >> $gitDataFile
echo -e "#define GIT_LAST_COMMIT_DATE    @\"$lastCommitDate\"" >> $gitDataFile
echo -e "#define GIT_LAST_COMMIT_COMMENT @\"$lastCommitComment\"" >> $gitDataFile
echo -e "#define GIT_LAST_REPO_TAG       @\"$lastRepoTag\"" >> $gitDataFile

And for the current state of my project, this produces the gitDataAutoGenerated.h file with the following contents:

// Auto generated file
// Created 2012-03-04 18:41:15

#define BUILD_DATE              @"2012-03-04 18:41:15"
#define GIT_CURRENT_BRANCH      @"master"
#define GIT_LAST_COMMIT_HASH    @"8988fe8"
#define GIT_LAST_COMMIT_DATE    @"2012-03-04"
#define GIT_LAST_COMMIT_COMMENT @"Toned down size of elements in preferences"
#define GIT_LAST_REPO_TAG       @"v0.01"

Which I include in my program as:

#import "gitDataAutoGenerated.h"
programBuildDate.text = BUILD_DATE;
programCreateDate.text = GIT_LAST_COMMIT_DATE;
programVersion.text = [NSString stringWithFormat:@"%@%@%@", GIT_LAST_REPO_TAG,([GIT_LAST_REPO_TAG length]>0?@".":@"") , [GIT_LAST_COMMIT_HASH uppercaseString]];

And I display this on an information page as:

So now if ever I get a bug report from this program, I can use the Git commit hash of 8988fe8 to go straight to the source and re-create exactly the program version that the user has. Of course if I was being really retentive I would have archived the software binary along with the source code! But thats a story for a different day.

Hope you all found this useful.