future page 3 - Dave's Blog

Thought Experiments and Design Principles

Raymond Chen has some thought experiments useful for discovering various kinds of stupidity in software design:

• What if two programs did this?
• Who says there's only one?
• Imagine if this were possible. / Imagine if things actually worked that way.

Tim Berners-Lee's principles of Web design includes my favorite: Test of Independent Invention. This has a thought experiment containing the construction of the MMM (Multi-Media Mesh) with MRIs (Media Resource Identifiers) and MMTP (Muli-Media Transport Protocol).

The Internet design principles (RFC 1958) includes the Robustness Principle: be strict when sending and tolerant when receiving. A good one, but applied too liberally can lead to interop issues. For instance, consider web browsers. Imagine one browser becomes so popular that web devs create web pages and just test out their pages in this popular browser. They don't ensure their pages conform to standards and accidentally end up depending on the manner in which this popular browser tolerantly accepts non-standard input. This non-standard behavior ends up as de facto standard and future updates to the standard essentially has had decisions made for it.

Android eBook Reader And Makers

I was reading Makers, Cory Doctorow's latest novel, as it was serialized on Tor's website but with no ability to save my place within a page I set out to find a book reading app for my G1 Android phone. I stopped looking once I found Aldiko. Its got bookmarks within chapters, configurable fonts, you can look-up words in a dictionary, and has an easy method to download public domain and creative common books. I was able to take advantage of Aldiko's in-app book download system to get Makers onto my phone so I didn't have to bother with any conversion programs etc, and I didn't have to worry about spacing or layout, the book had the correct cover art, and chapter delimiters. I'm very happy with this app and finished reading Makers on it.

Makers is set in the near future and features teams of inventors, networked 3d printers, IP contention, body modifications, and Disney -- just the sort of thing you'd expect from a Cory Doctorow novel. The tale seems to be an allegory for the Internet including displacing existing businesses and the conflict between the existing big entertainment IP owners and the plethora of fans and minor content producers. The story is engaging and the characters filled out and believable. I recommend Makers and as always its Creative Commons so go take a look right now.

Star Trek Thoughts

I watched the new Star Trek movie Thursday morning, along with many others who work on Windows. Microsoft rented out a theater and played the movie on all screens. I greatly enjoyed the movie!

Spoilers follow... I'm obviously not the biggest Star Trek nerd (or at least TOS nerd) since I didn't even pick up on the fact that Kirk's dad being dead was a discrepancy from the TV series. I only figured out the alternate time-line stuff when they killed most of the Vulcans. I was just surprised they didn't set right what once went wrong by the end of the movie with some more time travel magic to bring back Vulcan. On that note, I'm pretty sure the Spock-Spock conversation at the end, is Nimoy Spock sending Sylar Spock off to school so that Nimoy Spock can get freaky repopulating the Vulcan race. Although at first after his 'two places at once' comment I thought he was saying... something else. Also, was the main evil guy a random miner turned psycho? And his crazy looking spaceship that destroys the Federation fleet was just a mining vessel from the future? Once they invent time travel anybody can get drunk, go back in time, and conquer Earth.

Notes on Creating Internet Explorer Extensions in C++ and COM

Working on Internet Explorer extensions in C++ & COM, I had to relearn or rediscover how to do several totally basic and important things. To save myself and possibly others trouble in the future, here's some pertinent links and tips.

First you must choose your IE extensibility point. Here's a very short list of the few I've used:

• Explorer Bars and IE Toolbars
• IE Tools, IE Help, and IE Context Menu menu items
• IE Toolbar Buttons

Once you've created your COM object that implements IObjectWithSite and whatever other interfaces your extensibility point requires as described in the above links you'll see your SetSite method get called by IE. You might want to know how to get the top level browser object from the IUnknown site object passed in via that method.

After that you may also want to listen for some events from the browser. To do this you'll need to:

1. Implement the dispinterface that has the event you want. For instance DWebBrowserEvents2, or HTMLDocumentEvents, or HTMLWindowEvents2. You'll have to search around in that area of the documentation to find the event you're looking for.
2. Register for events using AtlAdvise. The object you need to subscribe to depends on the events you want. For example, DWebBrowserEvents2 come from the webbrowser object, HTMLDocumentEvents come from the document object assuming its an HTML document (I obtained via get_Document method on the webbrowser), and HTMLWindowEvents2 come from the window object (which oddly I obtained via calling the get_script method on the document object). Note that depending on when your SetSite method is called the document may not exist yet. For my extension I signed up for browser events immediately and then listened for events like NavigateComplete before signing up for document and window events.
3. Implement IDispatch. The Invoke method will get called with event notifications from the dispinterfaces you sign up for in AtlAdvise. Implementing Invoke manually is a slight pain as all the parameters come in as VARIANTs and are in reverse order. There's some ATL macros that may make this easier but I didn't bother.
4. Call AtlUnadvise at some point -- at the latest when SetSite is called again and your site object changes.

If you want to check if an IHTMLElement is not visible on screen due how the page is scrolled, try comparing the Body or Document Element's client height and width, which appears to be the dimensions of the visible document area, to the element's bounding client rect which appears to be its position relative to the upper left corner of the visible document area. I've found this to be working for me so far, but I'm not positive that frames, iframes, zooming, editable document areas, etc won't mess this up.

Be sure to use pointers you get from the IWebBrowser/IHTMLDocument/etc. only on the thread on which you obtained the pointer or correctly marshal the pointers to other threads to avoid weird crashes and hangs.

Obtaining the HTML document of a subframe is slightly more complicated then you might hope. On the other hand this might be resolved by the new to IE8 method IHTMLFrameElement3::get_contentDocument

Check out Eric's IE blog post on IE extensibility which has some great links on this topic as well.

FormToAccelerator Internet Explorer Extension

I've made an extension for Internet Explorer 8, FormToAccelerator which turns HTML forms on a web page into either an accelerator or a search provider. In the design of the accelerators format we intentionally had HTML forms in mind so that it would be easy to create accelerators for existing web services. Consequently, creating an accelerator from an HTML form is a natural concept and an extension I've been meaning to finish for many months now.

This is similar in concept to the Opera feature that lets you add a form as a search provider. The user experience is very rough and requires some knowledge of accelerator variables. If I can come up with a better interaction model I may update this in the future, but at the moment all the designs I can come up with require way too much effort. Install IE8 RC1 and then try out FormToAccelerator.

Phone Replacement For Grocery Card

Another use for my new phone is as a replacement for my grocery card, those little plastic cards with a bar code on them that the grocery store gives you to track your purchasing habits. I've previously gone to great lengths to increase space in my pockets by removing infrequently used keys and reducing my wallet to the essentials. So I was glad to get rid of the QFC card and replace it with a photo of its bar code on my phone. Since the important part of the QFC card is the bar code which is just an image of black lines, if your phone has a camera and a screen with a reasonable resolution you can take a photo of the bar code and later display it to a reader. I've so far been able to try it once and successfully at a normal checkout line, but the reaction from the checkout lady was enough that I may in the future just keep a card in my car. She was very excited, asked me what kind of phone I had, called over another checkout person and generally made a large fuss. Also the checkout people generally don't mind giving me a new card if I don't have one with me.

XSLT Meddler Script

I've made an XSLT Meddler script in my continued XSLT adventures. Meddler is a simple and easy web server that runs whatever JScript.NET code you give it. I wrote a script that takes an indicated XSLT on the server, downloads an indicated XML from the Internet and returns the result of running that XML through the XSLT. This is useful when you want to work with something like the Zune software or IE7's feed platform which only reads feeds over the HTTP protocol. I'll give more interesting and specific examples of how this could be useful in the future.