Mar26
In the third update to my crossword web app tutorial, I discussed CSS Canvas. I mentioned how potentially powerful the canvas can be, especially as an alternative to Flash, but I wasn’t able to provide concrete examples since I hadn’t personally done anything exceptionally extraordinary with it yet.
Well now I have the proof! A couple of weeks ago I was followed on Twitter by @canvasdemos. The Canvas Demos blog dedicates its time to tracking down and showcasing demos and tutorials for the HTML canvas element. Some of the examples they’ve uncovered are truly amazing and include games, 3D tests, music visualizers, etc. If you’re at all intrigued by the power of CSS Canvas, and are wondering how you can use it on your own site (or Web app), don’t hesitate to give their site a look!.
The image above is from Jacob Seidelin’s music visualizer. The demo creates an image of Thom Yorke to the music of Radiohead’s Idioteque. It’s worth checking out.
— Ryan
Mar25
Although it’s easy to get Javascript to read from an XML file, pulling out the appropriate data can sometimes be tricky. Here are some tips to help you tame the XML beast.
Part 6: Taming XML
Let’s look at a typical XMLHttpRequest again.
var url = 'xml/070814.xml';var xmlhttp = new XMLHttpRequest(); if (xmlhttp != null) {xmlhttp.onreadystatechange = stateChange;xmlhttp.open('GET', url, true);xmlhttp.send(null);} else {alert('Your browser does not support XMLHTTP.'); }} function stateChange() {if (xmlhttp.readyState == 4) {if (xmlhttp.status == 200) {/*A status of 200 means that the XML file wasloaded and parsed without error. At this pointyou'll want to sort through all of the data sothat it can be used by your program. I'll giveyou some tips on how to do this in the nextupdate.*/} else {alert('Problem retrieving XML data.');}}}
Figure 1. The basic structure of an XMLHttpRequest
continue reading »
Mar8
When I first started developing this crossword tutorial, I wanted the end game to access USA Today’s crossword XML feed directly and offer a new game each day. Sadly, their feed is secured. Although I can track it down, view its source in a Web browser, save to a local file and upload to my server, I cannot get my code to access the file directly from their server. Keep that in mind when we reach the end of this tutorial. You’ll be able to play one completed game, but don’t get too attached. There’s not much replayability.
Part 5: Importing From XML
Most programs, including games, require data. More often than not this data must be updated regularly so as to sustain the usefulness of the application. This type of data is usually stored externally (out of the application’s main code) since it makes very little sense to require the application’s user to download a new version of the program every day in order to receive the latest and greatest data. Therefore, with respect to our game, it makes a great deal of sense to store the data for each crossword puzzle in an external XML file. This way each puzzle can easily be loaded individually by referencing a different XML file.
continue reading »
Mar6
Unlike desktop applications, or native iPhone apps, whose code is pre-compiled with assets prepped and readily available in nearby bundles, Web apps are burdened with the task of downloading their assets (HTML, CSS, images, scripts, etc) in real time, as a user is attempting to interact with the app. In this context I’m referring to a Web site as an “app” since so many of today’s Web 2.0 sites are robust enough to be considered applications. Also, Apple has often referred to iPhone Web sites as Web apps. HTML, CSS and scripts are generally low weight files, a couple of kilobytes a piece (some are larger, but most aren’t) and can be downloaded quickly. Images, on the other hand, can be very large—upwards of 100K in some instances. Downloading large images can be time consuming, especially on mobile devices, therefore you can improve your application’s user experience by downloading images ahead of time.
This part of the tutorial is actually not going to explain proper procedures for preloading images. There are a number of methods available, all of which can be found by doing a simple Google search for “preload images”. This article will instead concentrate on ways to reduce the necessity of preloading altogether by means of self-contained data and CSS Sprites.
I’ll start off by briefing explaining the importance of CSS Sprites (since Part 4 below will explain how to use self-contained data). An in-depth discussion of CSS Sprites can be read on A List Apart. In a nutshell, a sprite map is a collection of smaller images mapped onto one large image. By combining images, you will reduce server requests and speed up download times. CSS Sprites especially come in handy when dealing with hovers.
continue reading »
