The function CGImageCreateWithMask() can take either a mask or an image as the second parameter, but it turns out that Core Graphics (at least on iOS) is pretty picky about what is an acceptable image for the mask.

I’ve seen this snippet of code suggested in a few places:

CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(image),
CGImageGetHeight(image), CGImageGetBitsPerComponent(image),
CGImageGetBitsPerPixel(image), CGImageGetBytesPerRow(image),
CGImageGetDataProvider(image), NULL, false);

the idea being that you create a mask with the pixels that are in the loaded image, but it turns out that this code is not 100% reliable either.

The truth of the matter is that CGImage is an incredibly versatile object. The bits that represent the image can be in a variety of formats, bit depths, and colour space. When you load an image from a file, you are not guaranteed what format those bits are going to be in—for example, there are reports online of how people can get image masks to work if they save it in one way from an image editing program, but not if they save it a different way (e.g. http://stackoverflow.com/questions/1133248/any-idea-why-this-image-masking-code-does-not-work )

Thus, I’ve found that the best and most reliable way to generate an image mask from an arbitrary image is to do this:

1. Create a bitmap graphics context that is in an acceptable format for image masks
2. Draw your image into this bitmap graphics context
3. Create the image mask from the bits of the bitmap graphics context.

The following function has worked well for me so far:

CGImageRef createMaskWithImage(CGImageRef image)
{
    int maskWidth               = CGImageGetWidth(image);
    int maskHeight              = CGImageGetHeight(image);
    //  round bytesPerRow to the nearest 16 bytes, for performance's sake
    int bytesPerRow             = (maskWidth + 15) & 0xfffffff0;
    int bufferSize              = bytesPerRow * maskHeight;
 
    //  we use CFData instead of malloc(), because the memory has to stick around
    //  for the lifetime of the mask. if we used malloc(), we'd have to
    //  tell the CGDataProvider how to dispose of the memory when done. using
    //  CFData is just easier and cleaner.
 
    CFMutableDataRef dataBuffer = CFDataCreateMutable(kCFAllocatorDefault, 0);
    CFDataSetLength(dataBuffer, bufferSize);
 
    //  the data will be 8 bits per pixel, no alpha
    CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceGray();
    CGContextRef ctx            = CGBitmapContextCreate(CFDataGetMutableBytePtr(dataBuffer),
                                                        maskWidth, maskHeight,
                                                        8, bytesPerRow, colourSpace, kCGImageAlphaNone);
    //  drawing into this context will draw into the dataBuffer.
    CGContextDrawImage(ctx, CGRectMake(0, 0, maskWidth, maskHeight), image);
    CGContextRelease(ctx);
 
    //  now make a mask from the data.
    CGDataProviderRef dataProvider  = CGDataProviderCreateWithCFData(dataBuffer);
    CGImageRef mask                 = CGImageMaskCreate(maskWidth, maskHeight, 8, 8, bytesPerRow,
                                                        dataProvider, NULL, FALSE);
 
    CGDataProviderRelease(dataProvider);
    CGColorSpaceRelease(colourSpace);
    CFRelease(dataBuffer);
 
    return mask;
}

Example of use:

UIImage *maskSource = [UIImage imageNamed:@"mask.png"];
CGImageRef mask = createMaskWithImage(maskSource.CGImage);

Then use the mask as you wish, for example in the aforementioned CGImageCreateWithMask() or CGContextClipToMask()

And don’t forget to dispose of the mask when you’re done. createMaskWithImage() returns the mask with a retain count of 1, and expects the caller to take ownership.

CGImageRelease(mask);

Some of the excerpts seem to be showing up empty. I’m not 100% sure of what is causing that, but I’ll look into it (I made some changes to FeedWordPress, so it’s likely something I did :)

Thanks!

When I started doing iPhone development, I looked for something similar for iPhone dev blogs. While there are a lot of iPhone developers out there blogging, I could not find a good aggregator out there. I did find Planet iPhone SDK, but it does not seem to be active (I tried contacting the owner, but did not receive a response). Planet Cocoa is good and quite active, but iPhone development is just part of the coverage there (the rest is Mac desktop development, which I don’t do myself).

Thus, I am starting Planet iDev. Armed with FeedWordPress and a free WordPress theme, I have cobbled together a simple blog aggregator. I should note that many of the blogs I am aggregating I found on this tremendously helpful post by Travis Dunn.

Having never run a blog aggregator before, I am unsure of the ethics and etiquette of Planet-style sites. I have no intention of financially profiting from other people’s hard work, nor do I want to negatively impact others’ endeavours. With that in mind:

• There will never, ever be ads on Planet iDev
• All authors are credited, and all articles link back to their original sources (as do all of the items in the Planet iDev feed).
• I have set up the WordPress install to not be indexed by search engines.

Regardless, if any blog owner wants to be removed from this aggregation, I will be more than happy to do so, and I offer my sincerest apologies.

On the other, if any iPhone developer out there wants their blog to be added to this Planet, simply email me at planetidev@gmail.com (or comment on this post) with your blog’s information, and it will be considered for inclusion. Preference will be given to blogs that focus on the development and production process, rather than blogs that are mostly for product promotion.

I still have some questions regarding Planet etiquette. While most Planet sites seem to include the entire contents of the aggregated blogs’ posts, I wonder if it would be more polite to only display an excerpt (but include the entire article in the feed). Please share any thoughts you have on this matter, or on Planet iDev in general.

I hope others out there find this resource valuable and useful, and I hope this helps encourage a sense of community. Thanks!

Visit Planet iDev.

The basic process of making your web app cacheable offline is, in theory, fairly straightforward, and generally well-documented at Apple’s website. I ran into some interesting headaches though.

Gotchas:

• First thing to note is that your web server must serve your cache manifest file with a MIME type of text/cache-manifest. This may mean editing mime.types to add a line that looks like this:

  text/cache-manifest   manifest

  or perhaps a line in httpd.conf that looks like this:

  AddType text/cache-manifest  .manifest

• The next thing that had me stumped for a while: while your web server may know how to take the URL http://example.com/webapp/ and automatically and invisibly serve up the file http://example.com/webapp/index.html, your offline web app knows nothing of this mapping of webapp/ to webapp/index.html. If the URL bar reads http://example.com/webapp/ and you save it locally using a home screen bookmark, it will fail to launch correctly if the device is offline, even if index.html file has been cached. The device simply does not know to look for webapp/index.html instead of webapp/. Thus, you must ensure that the URL bar reads webapp/index.html before the user makes a home screen bookmark.
• At first, I thought I would enforce the above with a tiny bit of JavaScript that simply reads window.location and redirects to window.location + "index.html" if the URL ends in a slash. This worked while online, but it broke my app when offline, even when the redirection was not taken. Why? It seems that any reference to window.location in your script is treated as network access. Since the device is offline, it generates an error alert.

  Instead, I made my app live at webapp/main.html, and created a small webapp/index.html file that simply redirects to main.html. (I could have used a server redirect inside of an .htaccess file instead, but I chose not to, for no particular reason.)

Tips:

• You can specify a custom icon for the home screen bookmark using a <link> element, like so:

  <link rel="apple-touch-icon" href="custom_icon.png" />

  If you don’t want iPhone to automatically apply the “shine” effect on your icon, use the following instead:

  <link rel="apple-touch-icon-precomposed" href="custom_icon.png" />

• Since iPhone OS 3.0, offline web apps can have custom splash screens, just a like a native app! Simply add a link element to your web page:

  <link rel="apple-touch-startup-image" href="/splash.png" />

If you want to see the results of all this, go to http://bunnyherolabs.com/iphone/xform/ on your iPhone or iPod Touch, then click the “+” (add bookmark) button and choose “Add to Home Screen.” Now you can click on the “Panorama” icon on your home screen to see the demo at any time, even when not connected to the internet.

But the following change caught my eye: in section 12.2, “Termination”:

12.2 Termination
This Agreement and all rights and licenses granted by Apple hereunder and any services provided hereunder will terminate, effective immediately upon notice from Apple:
…
(f) if You engage, or encourage others to engage, in any misleading, fraudulent, improper, unlawful or dishonest act relating to this Agreement, including, but not limited to, misrepresenting the nature of Your submitted Application (e.g., hiding or trying to hide functionality from Apple’s review).

(emphasis added)

So be careful, hidden-unlockable-feature-mongers. Apple could terminate your licence!

I love my iPhone (and developing for it) but I definitely would like to see more competition in this space. I think this ad hits home for those of us who are frustrated with the iPhone’s shortcomings. On the other hand, the style of the end of the video makes me think of trailers for horror movies. I’m not sure that’s such a good association to make!

This ad campaign also reminds me of the old Sega Genesis commercials back in the day:

As a Flash developer and geek, the technology seems pretty damn impressive to me. It actually includes the LLVM compiler? Wild.

Still, there are technical concerns, although to be fair, there are many months before CS5 ships. And for the moment, Flash-built apps won’t have access to things like the iPhone’s native UIKit controls, but they will have access to the accelerometer and multitouch (which at first I thought they did not).

Furthermore, as an iPhone developer, I have concerns, and in a way these concerns have less to do with Adobe’s actions than Apple’s: the single chokepoint that is the App Store and its review/approval system. It’s clear that Apple’s review system does not scale (longer and longer delays in approvals), and discoverability is bad enough as it is with the number of apps in the store now and the limited number of ways there are to browse and find things in the store.

If the iPhone app ecosystem was completely open, with many “stores” and multiple ways of finding and buying apps, I’d welcome Flash-built iPhone apps with open arms: the more the merrier. As it is, though, I worry a bit about the flood of muck as every Flash developer (over a million by Adobe’s count: A MILLION!) with a back catalogue of content tries to get their old code into the App Store.

Some obvious predictions:

• We’ll see more than a few Flash component libraries that emulate UIKit controls
• Apple will unofficially delay or reject Flash-built apps for the first while until/unless Adobe and Apple come to some kind of understanding (see the issues that PhoneGap apps have had in the past, and that uses all native SDKs!).
• Flash developers will find it more difficult than they expect to get their old code working well on the iPhone
• Many iPhone programming contracts will be lost as clients decide (correctly or incorrectly) that they can do their iPhone project in-house with Flash

Still, I have to admit I personally can’t wait to get my hands on the public beta of Flash CS5. I enjoy working with Flash and ActionScript.

According to the docs, the differences:

If you are writing code that runs on both 2.x and 3.0 that needs to get tricky with tabs, these changes are a nuisance.

Even more infuriating is that the Apple documentation isn’t complete. The section ends with the sentence fragment “If you are implementing….” Yes? If I am implementing what? And what do I do if I am?

Yes, I’ve already reported documentation error. No response though. My guess is they’ll just remove the sentence fragment instead of expanding on it :(

[edited: I made a mistake in the table the first time I posted this. Should be fixed now.]

Please check out My Monkey.

Time from submission to approval: 13 days.

It’s a simple app, an Objective-C port of my Flash monkey widget. I added support for multitouch, the accelerometer and custom image backgrounds chosen from the user’s photo library.

It was a pretty straightforward port. The main thing I had to get used to again (coming from ActionScript) was the lack of automatic garbage collection.

I don’t expect this app to tear up the charts or anything like that :) but mainly as an exercise in learning iPhone programming and the whole process from code to distribution.