Building apps for the Retina Display

by Miguel de Icaza

While adding Retina Display support to TweetStation I learned a couple of tricks that I figured would help other developers.

iOS 4 Points

Apple's Retina Display conveniently doubles the number of pixels on each dimension, the previous iPhone display had 320x480 pixels while the new new phone has 640x960 pixels.

To make existing applications run out of the box on these new displays Apple changed the units on the display and instead of using pixels they now use points. They are not really typographical points, but iOS "points". Both the old iPhones and the new iPhone have a resolution of 320x480 points.

This means that existing code that absolutely positioned views on the screen will get the views laid out in the same positions regardless of the device that the code is running on.

In UIKit points are interpreted based on the value of the UIView.ContentScaleFactor. If the value is 1.0 each point is mapped to one pixel. If the value is set to 2.0 each point is mapped to four pixels (2x on each dimension).

UIKit layout and CoreGraphics rendering primitives will automatically take this factor into account and position and render accordingly.


The Image loading routines have been extended to load higher-resolution images by default when you use UIImage.FromBundle. On Retina Displays the code will probe for a file@2x.ext filename when you request file.ext to be loaded. For example this loads the background texture you use:

	texture = UIImage.FromBundle ("Images/texture.png");

TweetStation's images are here.

Bitmaps and Inkscape

All the icons and images on TweetStation were done using Inkscape. When I exported the icons they would invariably look blurry. For example, this is from my first attempt at getting the swipe menu on TweetStation working:

I would just draw my icons on Inkscape and then export them as bitmaps. Inkscape would then anti-alias the result, you can see how the reply icon is not rendered properly:

The Inkscape FAQ contains this bit of information that is very useful if you are drawing small icons:

With the current renderer, it is not possible to completely get rid of antialiasing. However, it is possible to partially suppress it on export. Usually, antialiasing is unwelcome in horizontal and vertical lines which become "blurred". To work around this, make sure your horizontal/vertical edges are snapped on the pixel grid, and all strokes are a whole number of pixels wide. Then, export bitmap at the default 90dpi so that 1 px unit corresponds to 1 bitmap pixel. In the resulting bitmap, snapped color boundaries will be perfectly crisp.

These are the settings that I use now to export the same graphic:

I used guidelines on Inkscape to help me:

This is the new version of the icon before it gets composited with the background

To export the same image at high resolution, set the DPI in the dialog box to 180. Inkscape will automatically change the width and height for you.

The other problem that I had was related to my centering code, this is what the rewteet icon looks like from the menu above:

The blurry sides of the retweet icon were caused by the math code setting the X position of the image at a fraction of a point (0.5).

After fixing both problems and adding a nice backdrop shadow, this is what the menu looks like:

Graphics Context

Loading images with more pixels for the background texture and the icons wont do you any good if you are drawing the images yourself.

When you create a graphics context using the pre-iOS 4 APIs you will end up with a context that assumes that you are not aware of the Retina Display and hence will rescale your drawing up. When you create an image context of 100x100 points like this:

	UIGraphics.BeginImageContext (new SizeF (100, 100));

You will end up with a context that has 200x200 points, but will automatically double all of your pen widths and will scale any images up. If you had a high-resolution image, it will first be scaled down when rendering to the context, then scaled up when rendering the data.

To take advantage of the retina display you need to call a new method:

	UIGraphics.BeginImageContextWithOptions (SizeF size, bool opaque, float scale);

If you set scale to zero, it will pick 1.0 for old display and 2.0 for retina displays. I use this helper method to support both iOS 3.x and iOS 4.0:

	void BeginImageContext (SizeF size)
		if (Graphics.HighRes)
			UIGraphics.BeginImageContextWithOptions (size, false, 0);
			UIGraphics.BeginImageContext (size);

This is how the swipe menu is rendered at high resolution:


Apple's Supporting Resolution Independence document has more information.

Posted on 20 Jul 2010

Mono's Git Migration

by Miguel de Icaza

Mono's source code is being migrated to GitHub on July 22nd, starting at 9am Boston time.

We are psyched that Github was kind enough to host Mono's large repositories for free on their system. We are also taking advantage of their new Organizations functionality.

Gonzalo posted the following details about the migration:

We are moving our source code repository to GitHub.

On July 22nd ~9am EDT (1300 GMT) the subversion repository at "svn
+ssh://" will be set to read-only mode and
kept that way forever.

We estimate that the process of migrating all the projects and moving
them to GitHub will take more than 3 and less than 8 hours. Once it is
completed we will send an email to this list with URLs to the new
repositories, FAQs,...

If you have any questions about the migration, please ask them here and we will add them to our Git Migration FAQ.

Posted on 20 Jul 2010

Fresh Mono Baked

by Miguel de Icaza

Andrew just announced Mono 2.6.7, the version that is replacing our long-term maintenance release of Mono with plenty of bug fixes as well as the following new features:

  • Microsoft's ASP.NET MVC2 is now bundled with Mono.
  • Upgraded xbuild tool (Mono's msbuild)
  • Upgraded our LINQ to SQL (DbLinq)
  • Upgraded our Soft Debugger
  • We now publish CentOS/RHEL packages.

Our CentOS/RHEL packages install on /opt/novell/mono, just like our packages for SUSE Linux Enterprise and should not conflict with your own packages of Mono that you might have from some other sources.

Posted on 20 Jul 2010

Microsoft Licensing Changes for IronRuby and IronPython

by Miguel de Icaza

If you check the latest versions of IronRubyIronPython or the Dynamic Language Runtime you will see that Microsoft has now relicensed the code from the Microsoft Permissive License to the Apache 2 License.

Posted on 17 Jul 2010

Spaniard Anger Towards Mexicans

by Miguel de Icaza

It has been brought to my attention that the upcoming 200 year celebration of Mexico's independence from Spain on September 15th has lead to office unrest all across the country between teams that have both Mexicans and Spaniards working side-by-side.

Spain might have won the world cup, but Mexico upgraded from being a colony of Spain and being subject to the will of the Kings of Spain, to a democracy subject to the will of drug dealers.

To resolve this animosity, I propose we settle the score this September 15th with a cook-off between Spaniard food and Mexican food.

I propose the cook-off from the Novell/Cambridge team be held at my place the weekend before the festivities to settle the score before the celebrations take place. We will make delicious tacos. Gonzalo will be making a Paella.

Posted on 17 Jul 2010

New Mono Runtime Features

by Miguel de Icaza

With Mono 2.8 we want to make it very easy for developers to use the LLVM powered Mono engine and the new Mono Garbage Collector.

Previously users had to build Mono from source code and choose as part of their build whether they wanted the Mono VM to be powered by LLVM or not and whether they wanted to use the Boehm GC or the new Generational GC. Typically users would have to keep multiple parallel Mono installations.

This is no longer necessary.

Mono 2.8 by default behaves just like any other Mono, by default you get the regular fast Mono JIT with the Boehm GC.

You can then pass the --llvm flag to instruct the Mono runtime to use LLVM for code generation (much slower to JIT, but produces better code for long-running applications or compute intensive applications).

To use the new garbage collector you pass the --gc=sgen command line argument.


We wanted users to try LLVM, SGen or the LLVM/Sgen combination without having to modify all of their launch scripts or existing tools so we introduced a new environment variable that Mono parses on startup, the MONO_ENV_OPTIONS variable.

Mono will parse the contents of the MONO_ENV_OPTIONS variable as if the arguments had been passed in the command line, so you could do a full bootstrap of Mono's class libraries with both by doing:

	$ export MONO_ENV_OPTIONS="--llvm --gc=sgen"
	$ make

How to test LLVM and SGen

Update: Both the --gc=sgen and --llvm options depend on your architecture and operating system being supported by SGen and LLVM and depend on you compiling your runtime with these features.

SGen will be automatically enabled if your OS/architecture is supported when you run configure.

LLVM requires the installation of the LLVM libraries. We strongly recommend that you use our modified version of LLVM that has been extended to support various constructs required by .NET.

For more information on compiling LLVM and building your Mono with it, see our web page

Posted on 14 Jul 2010

GZip your downloads

by Miguel de Icaza

Gonzalo yesterday pointed me to a feature in the HTTP client stack for .NET that I did not know about.

If you want the server to gzip the response before sending it to you, set the AutomaticDecompression flag in your HttpWebRequest:

	var request = (HttpWebRequest) WebRequest.Create (uri);
	request.AutomaticDecompression = DecompressionMethods.GZip;

This will set the Accept-Encoding HTTP header to gzip when you make your connection and automatically decompress this for you when you get the response stream.

Update: on the comments there is a suggestion that Deflate is another option you can use, and you can combine both GZip + Deflate on the flags above.

Update2: Dennis Dietric emailed me to point out an important bit: if the server side does not support GZip or Deflate content, you will could get a 406 return code, so when dealing with third party web sites you need to be prepared to fall back and retry your request without compression in place. The relevant sections of rfc 2616 are 10.4.7, 14.1 and 14.3.

Posted on 09 Jul 2010

Microsoft MS-PL code in Mono

by Miguel de Icaza

Over the past couple of years Microsoft has been open sourcing some key .NET libraries under the MS-PL or Apache 2 license.

We are tremendously grateful to Microsoft for making these components open source. This has allowed us to distribute this in the past, and we are going to be bundling a lot more of it with Mono 2.8:

In Mono 2.8, the following assemblies and code come from Microsoft:

With Mono 2.8 we are going to default to the .NET 4.0 profile. So from the list above MEF, the DLR, OData and MVC2 become first class citizens in Mono-land, no longer third-party packages that you needed to install.

Update: as of July 17th 2010, the DLR, IronPython and IronRuby changed their licenses from MS-PL to Apache2.

Posted on 07 Jul 2010

First MonoTouch Book is out

by Miguel de Icaza

I am very excited to see the first MonoTouch book published.

You could not ask for a better team of authors to explain the MonoTouch and the iPhone platform. Chris, Craig, Martin, Rory, and Wally.

This book was a team effort by various active members of the MonoTouch community. They nurtured the community from the start by exploring MonoTouch, by reporting bugs and missing functionality in MonoTouch and by guiding .NET developers through the new world of building iPhone applications.

Congratulations on the book release guys!

You can find them here:

Posted on 06 Jul 2010

Pinta 0.4 Released

by Miguel de Icaza

Jonathan Pobst has released a new version of his paint program, Pinta, a lightweight app that runs on Linux, OSX and Windows and is built entirely using Gtk#.

In this version, Jonathan added the MonoDevelop docking library to allow users to reorder the editing tools to match their workflow:

There are ready-to-run packages available for Windows, OSX, Ubuntu and OpenSUSE.

Posted on 06 Jul 2010

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