links page 4 - Dave's Blog

View PDFs on Android

Irritatingly, my G1 won't show me PDFs so I've made the Google Docs PDF viewer which will load PDFs on the web up in Google Docs. Google Docs has the useful ability to display PDFs in web browsers without any Adobe software and works (mostly) on Android.

This was very easy to put together as an Android activity. First its necessary to register the application as handling PDFs from the web. This is done via the intent-filter declaration in the manifest:

   intent-filter
      action android:name="android.intent.action.VIEW"/
      data android:scheme="http" android:mimeType="application/pdf"/
      category android:name="android.intent.category.DEFAULT"/
      category android:name="android.intent.category.BROWSABLE"/
   /intent-filter

Second, the activity opens up the browser to Google Docs pointing to the PDF.

   Intent intent = new Intent();
   intent.setAction(getIntent().getAction());
   intent.setData(Uri.parse(
    "http://docs.google.com/gview?embedded=true&url=" + 
    percentEncodeForQuery(getIntent().getData().toString())));

   startActivity(intent);

Blog Layout and Implementation Improvements

I've redone my blog's layout to remind myself how terrible CSS is -- err I mean to play with the more advanced features of CSS 2.1 which are all now available in IE8. As part of the new layout I've included my Delicious links by default but at a smaller size and I've replaced the navigation list options with Technical, Personal and Everything as I've heard from folks that that would actually be useful. Besides the layout I've also updated the back-end, switching from my handmade PHP+XSLT+RSS/Atom monster to a slightly less horrible PHP+DB solution. As a result everything should be much much faster including search which, incidentally, is so much easier to implement outside of XSLT.

Eat Pants - Interactive Fiction Sessions from my Server Logs

I've looked at my web server logs previously to see if anyone had used my Web Frotz Interpreter and until recently didn't realize that awstats (the web server log report generator) was truncating the query from my URL, so I couldn't tell that anyone was actually using it. But after grepping the logs manually I've pulled out the URLs of visitor's text adventure sessions. If you'll recall, my Web Frotz Interpreter stores the game state in the URL so its easy to see user's game states in the web server logs.

I've put some of the links up on the Web Frotz Interpreter page. Some of the interesting ones:

• Apparently you can eat pants in Lost Pig.
• Someone teaches me that in Zork the egg goes in the display case.
• There's a creepy exchange in Galatea.

Infrared Paint Link Roundup

I like the idea of QR codes, encoding URLs and placing them on real world objects, but the QR codes themselves are kind of ugly. To make them less obvious I thought I could spray QR codes on to an object with an infrared reflective paint and shine infrared light on the QR codes, since most cameras, for instance the camera in my G1 phone, pick up infrared that our eyes do not.

In my search for infrared paint I've found a seller of IR ink (via programming forum) and an Infrared Paint Recipe (via IR FAQ).

In looking for this paint I've found that it comes up a lot in relation to the military for things like paint markers that are visible at night with proper equipment, and paint that absorbs IR light to make vehicles less obvious to night vision goggles. Even though the first reflects infrared light and the second absorbs it websites end up refering to both as infrared paint which made it difficult to search.

Additionally I found links to some other geeky infrared projects:

• Infrared goggles that block out all light except for the edge of infrared light that humans can perceive.
• A project to make infrared patterns and paint to screw with tourist video/photos.

Thoughts on registerProtocolHandler in HTML 5

I'm a big fan of the concept of registerProtocolHandler in HTML 5 and in FireFox 3, but not quite the implementation. From a high level, it allows web apps to register themselves as handlers of an URL scheme so for (the canonical) example, GMail can register for the mailto URL scheme. I like the concept:

• Better integration of web apps with your system.
• Its easy for web apps to do.
• Links to URNs can now take the user to the sites the user prefers for the sort of thing identified by the URN. For example, if I have a physical address in HTML, instead of making that an http link to Yahoo Maps, I can make the link a geo scheme URI and those who follow the link will get their preferred mapping site that has registered for that scheme. Actually, looking at the geo scheme's RFC, maybe I'd rather use some other URN scheme to represent the physical location, but you get the point.

• There's no way to know if you are the handler for a particular URL scheme which is an important question for web app URL protocol handler authors.
• There's no way to fallback to an http URL in the case that a particular URL scheme isn't registered. A suggested solution to testing the registration of a scheme is for browsers to provide an additional script method to check if a scheme is registered. I don't like the idea of writing script that walks over all my page's links and rewrites them based on that method. I'd much rather see a declarative and backwards compatible fallback mechanism, although I don't know what that would look like.
• There's no way to register for a namespace within the urn scheme URI, the info scheme URI, or the tag scheme URI. I want to register info:lccn/... (Library of Congress Card Number identifiers) to LibraryThing or Amazon and I want to register urn:duri:... (dated URIs) to the Web Archive, among other things.


• Will this result in a proliferation of unregistered URL schemes with clashing namespaces? The ESW Wiki notes why this would be bad.
• And last, although this is nitpickier than the rest, I don't like the '%s' syntax used in the registration method. I'd much rather pass in an URL template, like the URL template used in OpenSearch. If an URL template is used for matching rather than registering against a particular URL scheme, this could also allow for registering a namespace within a URN. For example something along the lines of: registerProtocolHandler("info:lccn/{lccnID}", "htttp://www.librarything.com/search_works.php?q={lccnID}", "LibraryThing LCCN")

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.