Posts from the “Blog” Category

Custom compiler flags in XCode

So I’ve been messing with compiler flags in XCode for the last hour or so, and it turns out I was totally misunderstanding things. If you get info on a project or target in XCode, there’s a “User-Defined” section at the bottom that allows you to create your own flags for use at compile time. However, these flags are not actually passed into GCC! (Mistake 1!) I assumed that adding a key-value pair to the list would pass the flag straight through to GCC, but it appears that they are for use in build scripts, etc…

To pass a custom flag through to GCC so that you can use it in #ifdef and #if macros at compile time, you have to add a User-Defined Setting called “OTHER_CFLAGS”. For my project, I set the value to “-DIS_PHOTO_CHAT=1″. At compile time, the exact text is passed as an argument to GCC. You can set different values in different targets – and I was able to conditionally include some code in a header file using #if (IS_PHOTO_CHAT==1)…

It seems like you can use XCode’s built-in flags like ${TARGET_NAME} and ${PRODUCT_NAME} to insert variables into the value of OTHER_CFLAGS, but if your target name has spaces, I think you’re at a loss. I tried to set -DTARGET_NAME=${TARGET_NAME} for about an hour, but the target name had a space and I can’t get GCC to accept the value (tried quotes… no luck…) I’m no command-line-compiler-whiz, so I’m sure there’s a trick, but Google hasn’t turned anything up.

I’m still surprised OTHER_CFLAGS wasn’t preset to “” in the target build settings. There’s an empty field for “Other Code Signing Flags” (which seems less useful!) Oh well… Guess XCode is in permanent beta anyway?

The Best WordPress Site Ever?

So I accidentally clicked an ad this afternoon and stumbled across, an online community for eco-friendly folks. I hadn’t even scrolled half way down their home page when I found myself thinking: “What was this built in?” Ecoki is quite possibly the best designed wordpress site I’ve ever seen. I had to look at the page source to figure it out.

It looks like it’s a completely custom template. Must have cost a fortune… It seems like there are only four staff authors on the site – so they’ve been pretty busy!

Creating a UIImage from a CGLayer

CGLayers are great for drawing – especially when things need to be drawn over and over again. Converting a CGLayer to a UIImage is another story, though. NetSketch uses CGLayers for the drawing canvas, but converts them to UIImages when you go to upload your drawing or email it to a friend. The code below shows how it’s done. The CGLayer is drawn into a bitmap CGContext of the same size, and then a CGImage is created around the CGContext. The CGImage can be turned into a UIImage, and you’re done!

Be sure to leave a comment if you find this function useful!

UIImage* UIImageFromLayer(CGLayerRef layer)
    // Create the bitmap context
    CGContextRef    bitmapContext = NULL;
    void *          bitmapData;
    int             bitmapByteCount;
    int             bitmapBytesPerRow;
    CGSize          size = CGLayerGetSize(layer);
    // Declare the number of bytes per row. Each pixel in the bitmap in this
    // example is represented by 4 bytes; 8 bits each of red, green, blue, and
    // alpha.
    bitmapBytesPerRow   = (size.width * 4);
    bitmapByteCount     = (bitmapBytesPerRow * size.height);
    // Allocate memory for image data. This is the destination in memory
    // where any drawing to the bitmap context will be rendered.
    bitmapData = malloc( bitmapByteCount );
    if (bitmapData == NULL)
        return nil;
    // Create the bitmap context. We want pre-multiplied ARGB, 8-bits
    // per component. Regardless of what the source image format is
    // (CMYK, Grayscale, and so on) it will be converted over to the format
    // specified here by CGBitmapContextCreate.
    bitmapContext = CGBitmapContextCreate (bitmapData, size.width, size.height,8,bitmapBytesPerRow,
    if (bitmapContext == NULL)
        // error creating context
        return nil;
    CGContextScaleCTM(bitmapContext, 1, -1);
    CGContextTranslateCTM(bitmapContext, 0, -size.height);
    // Draw the image to the bitmap context. Once we draw, the memory
    // allocated for the context for rendering will then contain the
    // raw image data in the specified color space.
    CGContextDrawLayerAtPoint(bitmapContext, CGPointZero, layer);
    CGImageRef   img = CGBitmapContextCreateImage(bitmapContext);
    UIImage*     ui_img = [UIImage imageWithCGImage: img];
    return ui_img;

Safari-style iPhone Checkbox

I was finishing up work on an iPhone app earlier today and needed to add a check box to the interface. Interface Builder provides a “checkbox-ish” control that slides between “On” and “Off” states but it didn’t fit in well with the rest of the app. I needed a smaller one like the one that Mobile Safari provides for web forms.

It was pretty easy to create using a UIButton, but I spent a few minutes putting together images for the different button states. Click the link below to grab ‘em – and leave a comment if you find them useful!

iPhone Safari-Style

NetSketch mentioned on Digg!

Check it out! I was looking at Digg this morning and noticed a post about “Apple iPhone Art.” It points to an article in the Telegraph with a gallery of art done by Steve Sprang, the author of Brushes. The description on Digg mentioned NetSketch, though. Kind of cool to see it on the front page!

A cheap math app – not a good idea?

Earlier this month, I put the finishing touches on Mathomatic and published it to the App Store. Mathomatic is a pretty small app for doing symbolic math. I needed it for a class I took in Signal Processing, and I figured it’d be useful to others as well. It expands and simplifies complex polynomials, takes derivatives and integrals, and a couple other cool things. I built it around the Mathomatic CAS, an open source computer algebra system written in C, and spent most of my time creating a beautiful equation renderer for the iPhone (hopefully to be open sourced soon!)

I decided to sell it for $1.99 because it seemed like a low price would A) increase sales and B) lead to fewer complaints about the limited feature set (After all – how much can you expect for $1.99?). After selling NetSketch for $5.99, I was curious to see how a low priced app would go. I’ve been considering lowering the price on NetSketch, and I thought it’d help determine the optimal price.

Well, it turns out you can expect a lot for $1.99 – at least in the U.S (Interestingly enough, Mathomatic has a much higher rating overseas!). Mathomatic got some bad initial reviews from people looking for more powerful features. The most popular complaints mentioned were:
– Only supports the variables X, Y, and Z
– No support for trigonometric functions
– No in-app help

These are all valid complaints, but they were all things I’d hoped to avoid by pricing the app low. The only other app I’ve heard of that offers similar functionality on the iPhone is SpaceTime, and it’s $19.99. It is, of course, a much richer application with more features and most likely some documentation.

So the real question is – do the people that purchase math apps for the iPhone care how much they cost? Maybe there’s really no space in the market for a “cheap” math app!

Custom UIWebView Navigation Controller

Download Drill Down Example
+ Controller Source
(1.6MB .zip)

The next version of NetSketch will include a community browser, allowing you to view uploaded drawings, watch replays, and leave comments without leaving the app. When I started working on the community interface, I looked to other apps for inspiration. Almost every app I’ve used on the iPhone use a sliding navigation scheme, giving you the feeling that you’re drilling down into content as you use the application. This interface is intuitive in a lot of contexts, and dates back to the original iPod. The Facebook app allows you to browse other people’s Facebook pages and uses a drill down navigation bar. This works well for the social-network space because you can drill down to look at information and then return to the first page quickly.

I decided to use a UINavigationBar and implement a similar drill-down interface for the community part of NetSketch. However, I didn’t want to create custom controllers for each page in the community. I wanted to be able to improve the community without updating the app, and I didn’t want to write a communication layer to download and parse images and custom XML from the server.
Read more

Stopping a Runaway WebView

It turns out, all of the WebViews you create on the iPhone are managed by a central object called WebCore. It seems to be some sort of singleton that takes care of loading content and managing resource loading threads – but it can lead to some interesting problems if you try to rapidly create, display, and release a series of WebViews.

The upcoming version of NetSketch uses WebViews to display community content, but it wraps the web content in an iPhone native navigation bar. That way, there’s a feeling of “drilling down” into pages in the community. (Think: facebook app). It makes it hard to tell the entire thing is  done with WebViews and you get some more user-friendly behavior (like using the top right button in the navigation bar to login/logout). After several iterations, I chose to implement this “drilldown” approach using a custom navigation bar and separate WebViews for each page. A “navigation stack” holds the WebViews of previous pages, and if you drill down too far, they are converted to UIImages and the actual WebViews are released. This behavior helps limit memory consumption, while allowing you to perform common actions quickly (going back and clicking another thumbnail, for example). Keeping images of very old views allows you to rapidly exit the interface without seeing blank pages or waiting for old pages to reload.

Unfortunately, my implementation seems to have run afoul of WebCore. It turns out that if you request a page in a WebView and attempt to release the WebView before it’s done loading, WebCore will attempt to send it delegate messages once it’s been destroyed – and throw exceptions all over the place. My first instinct was to call [webView stopLoading], but that is (apparently) asynchronous and doesn’t actually stop the WebCore from preparing some of the content. If you register an object as a WebView delegate, you’ll notice that you can still recieve webViewDidFinishLoad:(UIWebView *)webView after a stopLoading call.

I messed around with this for a while, and was almost ready to create a “ready-to-release” stack for webViews that were still loading. As a last resort, I tried calling [webView loadRequest: nil], and got some promising results. When you call loadRequest, the WebView  makes an asynchronous call to

[sourcecode language='c']

- (BOOL)webView:(UIWebView *)w shouldStartLoadWithRequest:(NSURLRequest *)r navigationType:(UIWebViewNavigationType)navigationType


When this call returns true, the WebView attempts to load the URL and realizes it is nil. It will almost immediately call – (void)webView:(UIWebView *)w didFailLoadWithError:(NSError *)error, and then it is officially DEAD. You can safetly release the WebView and its delegate without running the risk of further callbacks hitting deallocated objects.

This isn’t a perfect solution (read: it’s a ridiculous hack). It makes stopping and releasing a WebView a multi-step asynchronous process. However, unlike the [webView stopLoading] approach, it results in a consistent series of delegate callbacks that you can observe and also appears to work 100% of the time.

In my implementation, the navigation controller tells a WebView wrapper object to “unlink” the WebView. It detaches itself from everything and calls loadRequest:nil on the WebView. When the didFailLoadWithError: delegate call is received, the WebView is released, the delegate connection is broken and the wrapper is automatically released as well.

So far, so good.

But I still wonder – what exactly does stopLoading do?

The NDA is gone!

Apple has finally removed the NDA from non-beta iPhone software, so the community can finally come out of hiding. I can’t wait to actually – you know – talk to people! I’ve got a few things in the pipes for NetSketch, and hopefully I can post some tutorials and info here. Then this blog might actually be useful…

- Ben

NetSketch drawing on a shirt!

l0k1 posted a picture of this t-shirt in the NetSketch forums yesterday – made from a NetSketch drawing by another artist. Pretty cool! It’s nice to see stuff like this get put to use – I wasn’t sure anybody was actually using the “Download to Illustrator” option on the site. Seeing stuff like this really makes it worth going the extra mile for features like that. The shirt looks great!

iArtMobile went live earlier this week and it looks pretty cool. There’s a gallery where you can view artwork created on the iPhone. I’m a bit biased, but I think the NetSketch stuff looks the best :-)

I discovered another drawing app, Brushes, while I was looking at iArtMobile. I downloaded it and played around – and I think it’s the strongest pixel-based drawing app I’ve seen. It’s ridiculously fast and does textured brushes – something that a lot of people have been asking for in NetSketch. Of course, the tradeoff is that the drawing is only 320×480 and, although you can zoom, you can’t draw in any more detail once you zoom in. Oh well… It looks like they built a custom UIScrollView similar to the one in NetSketch, so the pan/zoom gestures are familiar! It’d be nice if we could standardize on that. Some of the other apps – like No.2. use some truly bizarre controls.