Archives for category: Trickery

Warning: this is a short-term solution, it may cause interesting results in future versions of the webOS SDK, so use wisely.

One minor frustration I’ve run into with making JavaScript webOS apps (games in particular) is the mousemove events don’t seem to fire very often on custom controls. This is particularly noticeable when users finger-paint on canvas tags or drag elements around. I suspect that this quirk in the webOS webkit was introduced as a performance improvement, but running up against it can be painful.

A fix I’ve discovered is this simple CSS addition to any elements which need higher resolution mouse movement (er, touch movement, whichever):

myelement {
    -webkit-user-drag: element;
}

Just put any valid CSS selector in place of “myelement” above, and you should notice a marked improvement in mouse movement precision for the element(s) in question.

This is not a future-proof solution, because if Palm’s webkit properly supports this CSS property in the future, your users will be dragging a shadowed version of the control around in ways you probably don’t want. Please be sure and test this with new SDK versions and be ready to take it out of your app at some point.

The last post revealed how a simple call to PalmSystem from your JavaScript code opens the door for you to take a stock web app with your favorite framework and turn it into a simple webOS app without having the overhead (or the wealth of cool features, in the interest of fairness) of Mojo.

Continuing with my explorations in the webOS 1.4.5 SDK, I’ve picked out a couple of other useful calls to the PalmSystem object. Both can be added to the “hello world” example I started in part one, and they’re really quick.

Free-wheeling orientation

A common requirement for mobile apps is the ability to respond to device orientation. I’m still digging around to see where you can hook into these events, but in the meantime here’s a simple call which is quite useful:

window.PalmSystem.setWindowOrientation('free');

This tells webOS to let your app rotate along with the device orientation, switching from portrait to landscape as necessary. It’s a high-value one-liner call which should serve most orientation needs.

You can also specify a “locked” orientation with different strings in place of “free”. Options are: up (default portrait), down, left and right. So if you have a side-scroller game that would benefit from horizontal presentation, just use:

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One neat discovery I found in the webOS 1.4.5 SDK is that it is possible to have a simple app which doesn’t use Mojo. Why would you want to? Load time! Mojo brings a lot to the table, but if you want to use your own favorite JavaScript framework, much of that ends up being overhead and increases your app’s load time.

Step one: Make a web app and test it in Chrome or Safari.

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html lang="en">
<head>
    <title>Hello</title>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body>
    <h1>Hello World!</h1>
</body>
</html>

Save this into a new folder (using a folder name of “hello” in this example) as index.html. This will become your app folder. You can test your app in Chrome or Safari by simply opening this file in your browser. Not terribly impressive, but hey, it’s a start.

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Wasn’t quite ready to put this out into the wild, but then I didn’t exactly set it to “private” on GitHub, now did I?

Check out the docs at: http://joapp.com/jo

The current dev build (with docs and libs built) is available for download at: http://github.com/davebalmer/jo/downloads

And the source is available at GitHub as well (freeBSD license): http://github.com/davebalmer/jo

Have fun, and remember that the framework is working, but still under development. Please send me feedback (especially bugs).

I’m also looking for collaborators (both JavaScript and CSS), so message me on GitHub if you’re interested.

Now that I have a break from my last job, I’ve been working feverishly on my new JavaScript app framework. Called “Jo”, one of the themes of the architecture is keeping the code simple by leveraging advanced CSS (finally) which is common among most modern browsers.

One of the issues I’ve run into with this approach in the past is the CSS gets thick with, basically, lots of div tags with classnames like “menubar” and “group”. I found this can make for some difficult maintenance, especially when working on cross-platform apps.

Worse, one of the first real apps I’m building with the new framework includes a searchable, indexed set of its own documentation. Cute thought, but hurdle one was: how the heck do I pull in HTML doc files with their interesting (and possibly themed) CSS without creating odd interference with my UI controls?

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