If you, like many Flash developers, are looking into using HTML5 for your web apps, you’ll almost certainly have come across jQuery. It’s a very popular JavaScript library, used by a large percentage of the most visited websites – but what’s all the fuss about, and should you use it?

Background

If you know AS3, you basically know a lot of JavaScript already; the two languages are very similar. So it’s tempting to just jump straight in and code – but there are a few important concepts you need to understand first. One of these is the idea of the DOM.

When you load a webpage, your browser turns flat HTML into a tree-like structure of JavaScript objects called the DOM (Document Object Model). The JavaScript DOM, then, is very similar to the ActionScript Display List; and if you’re a Flex developer, you’ll be able to see the similarities between MXML and HTML.

In Flash, we can access specific display objects by navigating to them through the display list, like stage.getChildAt(3).getChildAt(0), but this is pretty ridiculous. Instead, we’re more likely to give display objects instance names (through the Flash IDE), or store references to them in variables, arrays, or object properties, like dialogBox.okButton = new SimpleButton().

In JavaScript, we could construct our DOM entirely through JS and then tell the browser to render it, but this is an unusual approach; we’re much more likely to define the DOM via HTML, perhaps with a little JS augmentation. So, JavaScript has various different methods for accessing elements of the DOM.

The simplest of these is document.getElementById(). If we have an HTML document defined like this:

What if you wanted to then access the two p elements? We can’t access them directly with document.getElementById(), since they have no ID, but we can use document.getElementsByTagName("p") to obtain an array containing both of them.

And if we’d had another span, like this:

<div>
<span id="example1">
<p>Here's some example text.</p>
<p>More example text that we created on the fly.</p>
</span>
<span id="example2">
<p>A second span.</p>
<p>We don't care about these paragraphs.</p>
</span>
</div>

…and we only wanted to obtain the first two p tags, we could call document.getElementById("example1").getElementsByTagName("p") just to retrieve those two – all these DOM functions work at any level in the tree structure, just like how every Flash DisplayObjectContainer has methods like getChildAt().

This is simple enough to understand, but there are problems. The first, you may not be surprised to hear, concerns Internet Explorer.

Cross-Browser Compatibility

Impressive Webs has a great outline of Internet Explorer’s getElementById() problem. Essentially, if you have an HTML element like this:

<span name="exampleName"></span>

…then, in most browsers, document.getElementById("exampleName") will not give you the span in question, but in IE7, it will. (Other browsers could use document.getElementsByName("exampleName")[0] to return this particular span.)

This means that, to be consistent across browsers (and assuming we can’t change the HTML), we’ll need to write code like this:

var theSpan;
if (usingIE) { //I won't explain how to detect the browser here
var temp = document.getElementById("exampleId");
//this might have returned an element with a name of "exampleId", so we must check:
if (temp.getAttribute("id") == "exampleId") {
theSpan = temp;
}
}
else {
theSpan = document.getElementById("exampleId");
}

Great! But, unfortunately, there are so many of these irritating little differences; it will probably surprise you, if you’re coming from a straight-Flash background, where “compatibility issue” generally means that the Flash Player is a little slow on certain platforms.

jQuery solves this. It papers over the cracks between different browsers with its own set of functions, so if the user’s browser is at least as new as IE6, your code can have a consistent interface.

That’s not the only way that jQuery makes JavaScript simpler…

Easy Syntax

Let’s go back to this snippet of HTML, and assume we want to retrieve the highlighted p elements from the DOM:

<div>
<span id="example1">
<p>Here's some example text.</p>
<p>More example text that we created on the fly.</p>
</span>
<span id="example2">
<p>A second span.</p>
<p>We don't care about these paragraphs.</p>
</span>
</div>

With jQuery, we can just write:

jQuery("#example1 p")

That’s all we need! #example1 says “get the element with an ID of example1” and p says “get all the p elements that are children of that element”. It returns a “jQuery object”, which is a JavaScript object that contains the two p elements themselves from the JS DOM, plus a few extra properties and methods specific to jQuery.

We can make it even shorter still, by replacing jQuery with $ – there’s no mystery here; $ is just a short variable name. Compare it to native JavaScript code:

It’s not just shorter, it’s consistent with CSS, which makes it easy to pick up. We could use the exact same selector as inside our jQuery() call to style these specific paragraphs in a CSS stylesheet:

#example1 p { color: red }

That’s just a very simple example; I’m not going to go into detail, but I’m sure you can see the benefit of being able to use the same selectors in both CSS and jQuery.

More Than Just Selection

I mentioned that the jQuery objects returned by a $() call had additional methods and properties. These give you an easy syntax for writing other common pieces of code.

For example, we could add a mouse click event listener and handler function to both of those p elements like so:

In each case, jQuery provides a simple, short, consistent way of writing. It means it’s faster to get code from your head to the browser – and not just because it requires fewer characters.

Tweens and Transitions

Since Flash has its roots in animation, we’re used to it having plenty of tweening capabilities built in – both in the Flash IDE and in the Tween class, not to mention the various tweening libraries available.

JavaScript is different; animation is not an intrinsic part of the platform. But little tweens and transitions are expected parts of the user interaction of modern web app: if I add a new comment on a thread, it slides into place; if I remove an item from my shopping basket, it flashes red and disappears. Without these, apps look unpolished.

jQuery adds these little transitions.

For example, let’s say we want to make either of the aforementioned paragraphs fade out when they’re clicked. Easy:

$("#example1 p").click(function() {
$(this).fadeOut();
});

Nothing to it! And you can pass a duration and callback to the fadeOut() function, if you don’t like the defaults.

For something a little more powerful, we can use the animate() method. This is essentially the equivalent of a tween; pass it a set of CSS properties and values to animate towards, a duration, a type of easing, and a callback, and it takes care of it all for you.

It’s not exactly Greensock, but it’s far more convenient than writing these effects from scratch, and ideal for web app interfaces.

Speaking of which…

UI Widgets

HTML has a few UI components built in, of course: buttons, text fields, and so on. HTML5 defines a few new ones, like a pop-up calendar picker and color picket (though these are currently only supported in Opera).

But these aren’t enough, on their own, to make up a full, modern web app interface. There’s nothing to handle tabs within a page, or a progress bar, or even a simple dialog window (outside of alert() and prompt()).

jQuery UI, an optional library build on top of jQuery, adds these extra widgets, with methods and events that are consistent with the usual jQuery syntax. Think of it as a JavaScript equivalent to Keith Peters’ AS3 MinimalComps. The demo page shows it off better than I can explain it.

Every widget can support custom themes, so you can create a single skin that fits your site and apply it to every component, making it possible to modify their appearance all at once. Again: consistency! Plus, you can apply UI-related effects to other elements; make it possible for the user to drag or resize a DOM element, or click and drag a box around a group of elements to select them for submission.

Other Reasons jQuery is So Popular

The cross-browser compatibility, easy syntax, tween capabilities, and UI elements are the main benefits of jQuery over plain JS in my eyes. There are other reasons to like it, though:

It’s widely-used, and has been around for six years: it’s not some flash-in-the-pan “new hotness” that’s still unproven and might just die off in a few months. You can trust that it’ll be around for a while.

There’s a big community surrounding it: this means there are plenty of tutorials and books and forums and people to learn from; you’re not going to be fumbling around in the dark.

The documentation is excellent: seriously, take a look; it’s very clean and full of examples and demos

There are even alternative sets of docs with different interfaces, if that’s what you require (another example of the great community)

It’s open source: the community can add to it, and you can hack on it and learn from it

Paul Irish has twovideos breaking down what he learned from just running through the source

So why wouldn’t you use jQuery? As with most technology choices, it’s a question of making sure you’re using the right tool for the job. If you have a simple DOM structure, or don’t require fancy animations and transitions, or are mainly using the canvas to render your interface, rather than widgets, jQuery probably isn’t necessary.

If you’re already using one or more JavaScript libraries – Dojo, MooTools, YUI, etc. – you may well find that you don’t need jQuery’s functionality on top of what they offer. But my goal in this article is not to try to sell you on any particular library above any other.

I hope this article has helped to explain just what the big deal is about jQuery, particularly if you’re coming from the world of AS3 and Flash. If you’d like to learn it, check out the jQuery tag over on Nettuts+ – jQuery for Absolute Beginners is a good place to start.

10 Responses to “Why Bother With jQuery? A Guide for (Former) Flash Developers”

If you, like many Flash developers, are looking into using HTML5 for your web apps, you’ll almost certainly have come across jQuery. It’s a very popular JavaScript library, used by a large percentage of the most visited websites – but what’s all the fuss about, and should you use it?

Background

If you know AS3, you basically know a lot of JavaScript already; the two languages are very similar. So it’s tempting to just jump straight in and code – but there are a few important concepts you need to understand first. One of these is the idea of the DOM.

When you load a webpage, your browser turns flat HTML into a tree-like structure of JavaScript objects called the DOM (Document Object Model). The JavaScript DOM, then, is very similar to the ActionScript Display List; and if you’re a Flex developer, you’ll be able to see the similarities between MXML and HTML.

In Flash, we can access specific display objects by navigating to them through the display list, like stage.getChildAt(3).getChildAt(0), but this is pretty ridiculous. Instead, we’re more likely to give display objects instance names (through the Flash IDE), or store references to them in variables, arrays, or object properties, like dialogBox.okButton = new SimpleButton().

In JavaScript, we could construct our DOM entirely through JS and then tell the browser to render it, but this is an unusual approach; we’re much more likely to define the DOM via HTML, perhaps with a little JS augmentation. So, JavaScript has various different methods for accessing elements of the DOM.

The simplest of these is document.getElementById(). If we have an HTML document defined like this:

What if you wanted to then access the two p elements? We can’t access them directly with document.getElementById(), since they have no ID, but we can use document.getElementsByTagName("p") to obtain an array containing both of them.

And if we’d had another span, like this:

<div>
<span id="example1">
<p>Here's some example text.</p>
<p>More example text that we created on the fly.</p>
</span>
<span id="example2">
<p>A second span.</p>
<p>We don't care about these paragraphs.</p>
</span>
</div>

…and we only wanted to obtain the first two p tags, we could call document.getElementById("example1").getElementsByTagName("p") just to retrieve those two – all these DOM functions work at any level in the tree structure, just like how every Flash DisplayObjectContainer has methods like getChildAt().

This is simple enough to understand, but there are problems. The first, you may not be surprised to hear, concerns Internet Explorer.

Cross-Browser Compatibility

Impressive Webs has a great outline of Internet Explorer’s getElementById() problem. Essentially, if you have an HTML element like this:

<span name="exampleName"></span>

…then, in most browsers, document.getElementById("exampleName") will not give you the span in question, but in IE7, it will. (Other browsers could use document.getElementsByName("exampleName")[0] to return this particular span.)

This means that, to be consistent across browsers (and assuming we can’t change the HTML), we’ll need to write code like this:

var theSpan;
if (usingIE) { //I won't explain how to detect the browser here
var temp = document.getElementById("exampleId");
//this might have returned an element with a name of "exampleId", so we must check:
if (temp.getAttribute("id") == "exampleId") {
theSpan = temp;
}
}
else {
theSpan = document.getElementById("exampleId");
}

Great! But, unfortunately, there are so many of these irritating little differences; it will probably surprise you, if you’re coming from a straight-Flash background, where “compatibility issue” generally means that the Flash Player is a little slow on certain platforms.

jQuery solves this. It papers over the cracks between different browsers with its own set of functions, so if the user’s browser is at least as new as IE6, your code can have a consistent interface.

That’s not the only way that jQuery makes JavaScript simpler…

Easy Syntax

Let’s go back to this snippet of HTML, and assume we want to retrieve the highlighted p elements from the DOM:

<div>
<span id="example1">
<p>Here's some example text.</p>
<p>More example text that we created on the fly.</p>
</span>
<span id="example2">
<p>A second span.</p>
<p>We don't care about these paragraphs.</p>
</span>
</div>

With jQuery, we can just write:

jQuery("#example1 p")

That’s all we need! #example1 says “get the element with an ID of example1” and p says “get all the p elements that are children of that element”. It returns a “jQuery object”, which is a JavaScript object that contains the two p elements themselves from the JS DOM, plus a few extra properties and methods specific to jQuery.

We can make it even shorter still, by replacing jQuery with $ – there’s no mystery here; $ is just a short variable name. Compare it to native JavaScript code:

It’s not just shorter, it’s consistent with CSS, which makes it easy to pick up. We could use the exact same selector as inside our jQuery() call to style these specific paragraphs in a CSS stylesheet:

#example1 p { color: red }

That’s just a very simple example; I’m not going to go into detail, but I’m sure you can see the benefit of being able to use the same selectors in both CSS and jQuery.

More Than Just Selection

I mentioned that the jQuery objects returned by a $() call had additional methods and properties. These give you an easy syntax for writing other common pieces of code.

For example, we could add a mouse click event listener and handler function to both of those p elements like so:

In each case, jQuery provides a simple, short, consistent way of writing. It means it’s faster to get code from your head to the browser – and not just because it requires fewer characters.

Tweens and Transitions

Since Flash has its roots in animation, we’re used to it having plenty of tweening capabilities built in – both in the Flash IDE and in the Tween class, not to mention the various tweening libraries available.

JavaScript is different; animation is not an intrinsic part of the platform. But little tweens and transitions are expected parts of the user interaction of modern web app: if I add a new comment on a thread, it slides into place; if I remove an item from my shopping basket, it flashes red and disappears. Without these, apps look unpolished.

jQuery adds these little transitions.

For example, let’s say we want to make either of the aforementioned paragraphs fade out when they’re clicked. Easy:

$("#example1 p").click(function() {
$(this).fadeOut();
});

Nothing to it! And you can pass a duration and callback to the fadeOut() function, if you don’t like the defaults.

For something a little more powerful, we can use the animate() method. This is essentially the equivalent of a tween; pass it a set of CSS properties and values to animate towards, a duration, a type of easing, and a callback, and it takes care of it all for you.

It’s not exactly Greensock, but it’s far more convenient than writing these effects from scratch, and ideal for web app interfaces.

Speaking of which…

UI Widgets

HTML has a few UI components built in, of course: buttons, text fields, and so on. HTML5 defines a few new ones, like a pop-up calendar picker and color picket (though these are currently only supported in Opera).

But these aren’t enough, on their own, to make up a full, modern web app interface. There’s nothing to handle tabs within a page, or a progress bar, or even a simple dialog window (outside of alert() and prompt()).

jQuery UI, an optional library build on top of jQuery, adds these extra widgets, with methods and events that are consistent with the usual jQuery syntax. Think of it as a JavaScript equivalent to Keith Peters’ AS3 MinimalComps. The demo page shows it off better than I can explain it.

Every widget can support custom themes, so you can create a single skin that fits your site and apply it to every component, making it possible to modify their appearance all at once. Again: consistency! Plus, you can apply UI-related effects to other elements; make it possible for the user to drag or resize a DOM element, or click and drag a box around a group of elements to select them for submission.

Other Reasons jQuery is So Popular

The cross-browser compatibility, easy syntax, tween capabilities, and UI elements are the main benefits of jQuery over plain JS in my eyes. There are other reasons to like it, though:

It’s widely-used, and has been around for six years: it’s not some flash-in-the-pan “new hotness” that’s still unproven and might just die off in a few months. You can trust that it’ll be around for a while.

There’s a big community surrounding it: this means there are plenty of tutorials and books and forums and people to learn from; you’re not going to be fumbling around in the dark.

The documentation is excellent: seriously, take a look; it’s very clean and full of examples and demos

There are even alternative sets of docs with different interfaces, if that’s what you require (another example of the great community)

It’s open source: the community can add to it, and you can hack on it and learn from it

Paul Irish has twovideos breaking down what he learned from just running through the source

So why wouldn’t you use jQuery? As with most technology choices, it’s a question of making sure you’re using the right tool for the job. If you have a simple DOM structure, or don’t require fancy animations and transitions, or are mainly using the canvas to render your interface, rather than widgets, jQuery probably isn’t necessary.

If you’re already using one or more JavaScript libraries – Dojo, MooTools, YUI, etc. – you may well find that you don’t need jQuery’s functionality on top of what they offer. But my goal in this article is not to try to sell you on any particular library above any other.

I hope this article has helped to explain just what the big deal is about jQuery, particularly if you’re coming from the world of AS3 and Flash. If you’d like to learn it, check out the jQuery tag over on Nettuts+ – jQuery for Absolute Beginners is a good place to start.

Hey Flash developers! In this tutorial series we are going to go through the process of developing a very basic Tower Defense game. In this first part of the series, we’ll learn how to deploy turrets on the game field, give them the ability to aim at an object (in this case, the mouse) and make them fire particles.

Final Result Preview

Once we complete this tutorial, we are going to have this:

Click a circle to mount a turret on it. Notice how all the turrets rotate so that they point towards the mouse cursor. Click, and all mounted turrets will fire a particle towards the cursor.

Step 6: Turret – Creating the Class

As I mentioned before, the turret is going to be a separate class. This is because turrets need to have specific properties and methods of their own, and to be extended in future to create different type of turrets. This makes them a perfect candidate to be defined in a separate class.

Go on and create a new class called Turret, derived from Sprite, in a file named Turret.as. It should have the following basic code:

Step 7: Turret – The Graphics

Now that we have base structure of the Turret class, the next step is to give the turret some graphics. For that we create a new function called draw() in the class. So put the following function just below the constructor:

As you might have noticed in the code, we draw a circle and a rectangle on it. That’s how our turret is going to look. Now we call this function from the constructor itself.

public function Turret()
{
draw();
}

Step 8: Creating a Ghost Turret

The next thing we do is to display a ghost turret when we hover the placeholders that we have put on the game field. What is a ghost turret? Well, its just a transparent turret that appears when hovering the mouse on the placeholders, to tell the player that a turret can be deployed there.

To begin with this, we need a ghost turret. Go ahead and declare a variable for it in the Main class.

In the above code we lower down the opacity of the turret to half (0.5) and set the mouseEnabled property of the turret to false so that the ghost turret does not receive any mouse events. Why? We will see that later. And as the ghost turret will be invisible by default, we hide it.

If you run the movie now (Ctrl+Enter), all you’ll see is three placeholders on the stage. Boring huh? Lets add some interactivity.

Step 9: Showing/Hiding the Ghost Turret

We want the ghost turret to appear when the mouse hovers over any placeholder. So let’s attach mouse listeners to each placeholder in the createTurretPlaceholder() function just before it returns the placeholder variable.

This is simple…we position the ghost turret to the placeholder’s cordinates and make it visible. Run the movie and you should see the ghost turret appear when hovering over the placeholders. Nice!

Step 10: Deploying Turrets

Our next objective is to deploy a turret when a placeholder is clicked. For that we need a CLICK listener on the placeholder. But before that we need an Array variable which will hold all our turrets, so we can reference them at any time later. Make one in the Main class.

private var turrets:Array = [];

Then attach another listener just below the two previous listeners we added in the createTurretPlaceholder() function:

One thing to note here. Remember we set the mouseEnabled property of the ghost turret to false? If we hadn’t, the ghost turret in between the placeholder and mouse would have captured the click event, thus preventing the event from reaching the placeholder. As a result the CLICK listener attached to the placeholder would not have get called.

You might want to remove the CLICK listener from the placeholder. I haven’t done it here since the new turret blocks any clicks, but if you use a different turret design, it’s a good idea.

Well thats all we need to place our turrets. Try running the movie and you should be able to deploy turrets on placeholders.

Step 11: Making the Turret Move

For this tutorial we will make the turret rotate to face the mouse. We’ll keep the rotation functionality in a separate method of the Turret class. This method will be called update().

All we do in ths function is calculate the angle of the mouse from the turret and set the turret’s angle to it. (Take a look at Trigonometry for Flash Developers if you’re not sure how this works.)

But notice that we have not called this function from anywhere and so nothing happens yet. This function will be called from the game loop that we define next. Lets go!

Step 12: The Game Loop

Whats a game loop? Its a function that is attach to the ENTER_FRAME event and so it gets called on every frame. It updates all the elements in the game…in our case, Turrets. More details in this article.

Create a function called gameLoop() below the Main() constructor which will be a listener to the ENTER_FRAME event of the movie:

private function gameLoop(e:Event):void {
}

Now that we have the listener function defined, we need to attach it to the corresponding event. We do so in the Main() constructor. Add the following line to the Main() function:

Step 15: Creating the Bullet

Before we proceed to writing the code for shooting in the shoot() function, we will define a new function for creating a bullet, just like we did for creating a placeholder. So put the following function below the createTurretPlaceholder():

Nothing much here. We just create a new Sprite, draw an off-white color circle inside it, and return it. Now let’s continue to define our shoot() function.

Step 16: How to Shoot?

Time to add some code to the shoot().

for each(var turret:Turret in turrets) {
}

First, we iterate over all the turrets on the stage using the for each...in loop.

var new_bullet:Sprite = createBullet();

Now for every turret we create a bullet using the function we created previously.

new_bullet.rotation = turret.rotation;

Here we store the value of turret’s rotation property in bullet’s rotation. Why? Well…rotating the bullet is not what we want. The bullet needs to continue moving in direction determined by the turret, and for this we need the turret’s rotation value from the time it shot the bullet. We just store this as the bullet’s rotation for future use.

These two lines set the bullet’s initial position, which is 25 pixels away from the turret in the direction of facing (remember the rotation property). Again, read up on trigonometry if this is unfamiliar to you.

addChild(new_bullet);

And as the usual last step, we add the bullet to the stage’s display list.

Step 17: Why Did That Extra Bullet Appear?

Any event which gets generated passes through three phases: capturing, target and bubbling. The events starts from the topmost parent of the target which generated the event. It passes through all the inner child elements, which is the capturing phase. Then it reaches the actual target which is the target phase. Then the event goes back to the top, passing through same elements in reverse, which is the bubbling phase. In the bubbling phase, all the elements which have a listener defined for the propagating event get triggered and their listeners are executed.

We have a CLICK listener bound to the stage and the placeholders. But the placeholders are also children of the stage. So when we click the placeholder, a CLICK event gets generated with the target as the placeholder. The event propagates from the stage towards the placeholder – the capture phase. It reaches the placeholder and its CLICK handler, the addTurret() function, gets executed and we have a turret on the stage. Now the event propagates backwards – the bubbling phase – and when it reaches the stage again it finds a CLICK listener for it as well, which gets executed. As a result the shoot() function gets executed and a bullet is added to the stage.

So thats the problem, but how to solve it? What we need to do is stop the event’s further propagation when it reaches the target. That means in the addTurret() we stop the event’s propagation. So go ahead and add a line at the end of addTurret():

The line we added stops the event’s propagation and it doesn’t reaches the stage. For a more comprehensive understanding of event framework in Actionscript 3.0 read the AS3 101 post. Let’s continue with the game.

Step 18: Making the Bullet Move

We create the bullet on clicking the stage but it doesn’t move still. Our next step is to add an event listener to the bullet which gets called on every frame and moves it. First, we declare a variable for the bullet’s speed. Add the variable where the other variables are declared:

If you test you game now, you should see bullets moving when you click on the stage. But if you look carefully, you will notice that the bullets keep moving once created…even after they go out of the visible stage area. Our next step is to destroy the bullets as soon as they leave the movie boundaries.

Here we check whether the bullet is out of the stage boundaries. If it is, we remove its ENTER_FRAME listener and remove the actual bullet from the stage. We also set the bullet variable to null so that the bullet has no reference left and is available for garbage collection.

Conclusion

We have completed our basic tower defense game in which you can deploy turrets on specific placeholders which shoot towards any point we click on the stage. Cool, huh?

In the next part we’ll add enemies to the game and intelligence to the turrets so that they can do what they are suppose to do: defend. Also we’ll add some more elements that make the game look more complete and cool. Till then, try adding some more features to this on your own.

Read the Full Tutorial

Tuts+ Premium Membership

We run a Premium membership system which periodically gives members access to extra tutorials, like this one! You’ll also get access to Psd Premium, Vector Premium, Audio Premium, Net Premium, Ae Premium, Cg Premium, Photo Premium, and the new Mobile Premium too. If you’re a Premium member, you can log in and download the tutorial. If you’re not a member, you can of course join today!

There are a lot of games out there with jerky, unrealistic movements and that can do only one thing to your product: make it unappealing to the audience. But smooth movement is not hard to achieve – let’s get to work!

Final Result Preview

Let’s take a look at the final result we will be working towards:

Step 1: Set Up the Environment

This is a straight forward tutorial, so the setting up will also be straight forward.

Create a New ActionScript 3.0 Flash Project. The stage size and color don’t matter, just use what you are confortable with.

I use FlashDevelop for coding, but also this could be done in any AS editor, like Flash Pro (or any text editor, maybe Notepad ). So, create a Class file, make sure your code looks pretty much like mine; see below. I called mine “Movement”. (If you’re using Flash Pro, check out this guide to creating a class.)

This is pretty much all that we’ll do for creating the object. You can use your own object but for this simple movement tutorial I used this simple square.

Step 3: Introducing the Input.as Class

Hi guys, this is the Input.as Class; Input.as Class these are the guys I told you about – be nice to them!

So what is this class about, you may wonder. Basically it does your key handling job for you. It adds a listener to ENTER_FRAME events – with low priority – and a key listener which fills some private Dictionaries. Also it uses another Class for key codes. You can take a look inside and see for yourself how is working.

//Example of Input.as Class usage
//You have to always initialize it as this with the stage parameter
Input.initialize(stage);
//After initializing, you can use kd(), kp() or ku() methods, which
//return a Boolean value if the conditions are met.
//These methods accept multiple arguments,
//so for one event you can use multiple keys.
//This makes it a lot easier to give a boost of accessibility to your app.
//e.g See below as I use one call for detecting UP arrow or W for going up.
Input.kd("UP", "W");

Step 4: Importing the Classes

So now that you are familiar with the Input.as Class, we are going to import it in our Movement Class and initialize it.

Step 5: Handling the Key Inputs

I use an ENTER_FRAME-based loop for detecting the key inputs; below is the refresh() method which is the handler function for this event.

private function refresh(e:Event):void {
//Key Handler
if (Input.kd("A", "LEFT")) {
//Move to the left
}
if (Input.kd("D", "RIGHT")) {
//Move to the right
}
if (!Input.kd("A", "LEFT", "D", "RIGHT")) {
//If there is no left/right pressed
}
if (Input.kd("W", "UP")) {
//Move up
}
if (Input.kd("S", "DOWN")) {
//Move down
}
if (!Input.kd("W", "UP", "S", "DOWN")) {
//If there is no up/down action
}
}

Step 6: Explaining the Calculations – Handling the Velocity

This is pretty straight forward. Detect whether any of the keys are pressed, then act accordingly.

I use the ternary operator a lot: value = condition ? true : false;
This is basically an if-statement that’s been condensed to a single line.

For every key detection, I use this method: if the value is bigger than _max then set it equal to _max; otherwise, increment or decrement that particular value as appropriate. This way, it’s kept within certain bounds. Simple, right?

If you’re unfamiliar with the ternary operator, grab a piece of paper and a pen and write out a few of them in if…else format; it’s a great exercise to get to grips with that’s going on.

Keep in mind I manipulate the dx and dy variables, and only set the actual x and y values at the end. This helps us make the motion fluid; it’s not jerking around as we alter their values directly throughout the function..

Go on, test it! See how nicely it’s moving?

Step 7: Handling Boundary Collisions

Okay. Everything is right, moving fluidly – but OUT of the stage! Below I added the collision detection conditions.

It’s looking for boundaries in a more precise fashion, by checking whether the edges of the square hit the boundaries (before this, it was just checking the center of the square against the boundaries).

Great. Now we need to add the code to make the square bounce off the boundaries. What I do for that is multiply by -1 the axis value dx or dy. But that is not enough! If the speed is quite fast, then the square will get through the margins or just go nuts. So before we multiply we need to set the x or y of the object to be the same as the boundary that it meets.

So if x < 0 (and so it is colliding with the left edge), then we move the object to be exactly on the left edge, like so: object.x = 0; and then multiply the dx by -1.

As HTML games begin to gradually increase in popularity, vendors are starting to introduce some exciting new APIs to make gaming that little bit sweeter for both us developers and our end players. One of these is the GamepadAPI, which allows you to connect your good old console gamepad into your computer and use it for browser based games, plug and play style. Let’s dive in!

Introduction: What Is the Gamepad API?

In a nutshell, the Gamepad API allows you to interact with your browser using a video game console controller, AKA a gamepad. This doesn’t require a special driver or plugin to work, it’s as simple as plug and play!

Being a console gamer rather than a desktop gamer myself, I much prefer to interact with games using a gamepad, and with the upcoming rise of HTML and JavaScript based games, this is going to become a really useful tool in making games more easily accessible for your users.

The Gamepad API is not readily available for public release, but we can start using it for ourselves with preview versions of Firefox. So before we get stuck in, we need a few things.

What You’ll Need

As I mentioned, the Gamepad API isn’t available for public release just yet so you will need to first get yourself a Nightly build of Firefox and make sure you have the Firebug add-on installed (for debugging purposes only).

Also, you can’t forget a gamepad! I’m going to be using a PlayStation 3 controller for this tutorial but an Xbox controller will do just fine.

The connection of a gamepad is detected with a simple JavaScript event listener, the event fired is called “MozGamepadConnected”. So the first thing we need to do is add an event listener to the window to detect that event.

I’m also adding a callback function that will log the details of the event to Firebug’s console. This is the information we are most interested in and what will actually let us know that we have connected a gamepad successfully.

If you’re gamepad is still connected, refresh your page (which you’ll see connected event be logged) and then disconnect your gamepad by ejecting it from the USB port. You should get an event log like this one.

Now we know when a gamepad has been connected and disconnected, it’s probably a good idea to record the state inside a variable and get ready to detect button events!

Step 3: Detecting Button Presses

Button presses, again, use an event listener and callback function with two events, “MozGamepadButtonDown” and “MozGamepadButtonUp”.

I would suggest logging the entire event from the button press yourself to see what is going on, but the key piece of information we need to get from this event is evt.button. This is the numerical id of the button that was pressed.

The callback function this time takes a second parameter, a boolean value to test if the button was pressed or released. We set this ourselves in the callback functions of the event listeners.

There is only one event fired by both analog sticks; each event gives us one of four possible axis and a value between -1.0 and +1.0. Axis 0 and 1 belong to left analog stick and axis 2 and 3 belong to the right.

In the diagram above you’ll see axis 0 and 2 correspond to the x axis, and 1 and 3 correspond to the y axis. By using both the x and y axis for each individual analog stick, you can figure out which way the analog stick is facing!

On different gamepads, you may have other axes. For instance, the shoulder triggers on an Xbox controller are also analog.

Step 5: Putting It Into Practice

That covers all of the events that we can currently take from a gamepad, so let’s put what we’ve learnt into practice.

Now, I don’t want to go too heavily into the game development side of things, as we are focusing on what we use to control games themselves. One of the key things to look at, though, is switching control schemes. As not everyone will have a gamepad ready to hand, we need to make sure we provide controls for both the keyboard and gamepad.

Step 6: Setting Up Your Canvas

To get a small demo up and running, create a canvas element in your html file with an id of “game” and set the width to 600 and height to 540. As you may know, the canvas element is commonly used to render HTML games on.

You will also want to copy the “ship.png” and “space.jpg” images from the source download to your working folder as these are what we’ll be rendering to the canvas. Alternatively, find some graphics of your own to have a play with!

Step 7: Creating the Game Loop

Now that the canvas element is in our DOM, we want to create a game loop to render our game.

I’m using a shim for “requestAnimationFrame” by Paul Irish that will be the base for our loop. Next, we get the 2D context of the canvas which we’ll use to draw on and create two new image objects, one for the background and one for our spaceship.

Next, the player object. It has x and y coordinates which keep track of where it should appear on the canvas; four direction states (up, down, left and right) so we can know which way the ship is moving; a render() function, which first calls updatePosition() and then draws the image of the ship onto the canvas based on the x and y coordinates, and finally the updatePosition() function itself, which tests to see which way the ship is set to move and updates its position accordingly.

Your canvas should now have a nice space looking background with a spaceship sat in the middle of it – not too exciting, I know. So let’s add some controls!

Step 8: Hooking Up the Ship’s Controls

In our player code we named the four buttons which we want to control our ship with. These match up to the names of the buttons inside the ps3Buttons[] array. So, all we have to do is modify our buttonPressed() function ever so slightly and we’ll be moving.

Head back over to your demo and you should be able to move your ship around!

Step 9: Adding a Keyboard Fallback

As not everyone playing your game will have a gamepad, you’ll probably still want to allow them to play the game with a keyboard.

Lets first create a new keys[] array, and map the keyboard’s arrow keys’ keyCode properties to the equivalent buttons on the gamepad. This will allow us to reuse buttonPressed() function that the gamepad utilises.

Now we need a “onkeyup” and “onkeydown” event listener for the arrow keys. When a key is pressed or released, we make sure that a gamepad is not in use. Then we prevent the arrow key from doing its usual task (scrolling the browser window up or down in this case) and then call the same buttonPressed() function that the gamepad calls.

To do this, a fake event object is passed with the key’s “keyCode” mapped to an item in the keys[] array, which in turn, passes the corresponding gamepad button ID.

This should now let you use the arrow keys for controlling the ship when a gamepad isn’t plugged in, while still letting the gamepad take over when it’s present.

Conclusion

So we’ve covered the basics of connecting a gamepad to your computer, learnt how to hook into the events that the gamepad fires, and then use them in practice. Not forgetting, the crucial fall-back support for the keyboard!

A quick challenge for those of you with a controller other than a PS3 Dual Shock: adjust the button mapping based on whichever controller is plugged in.

Thank you for taking the time to learn about the Gamepad API. If you have any questions, please leave them in the comments.

In the previous Quick Tips, we’ve looked at collision detection: essentially, detecting that two shapes have overlapped. Now, we’re ready to look at collision reaction: making something happen due to a collision. In this Quick Tip, we’ll look at the reactions of reflection and sliding.

Final Result Preview

Let’s look at the end result we’ll achieve at the end of this tutorial. Each Flash demo has a restart button; click it to reset the position of the circles at the top of stage.

The first demo shows off reflection:

The second shows sliding:

Step 1: The Reflection Formula

I’ve run through this topic several rounds with students, and experience has taught me that the head-on approach of explaining vector math to freshers results in blank faces and confused minds. So instead of putting up a Math lecture here, I shall refer those who are interested in investigating this topic further to Wolfram’s page on reflection.

Now, observe the diagram below. A is the circle’s velocity before a collision, and A’ is its velocity after the collision.

It’s obvious that A' = A + 2 V(Ap), where V(Ap) represents the vector with a magnitude of Ap, in the direction of the left normal. (You can see this by following the dashed lines.)

In order to obtain V(Ap), we shall project A onto the left normal.

Step 2: Implementation

Here comes the ActionScript implementation of reflection. I’ve highlighted the important parts. Line 67 – 69 is to calculate V(Ap) (v_leftNormSeg2) and line 70 implements the formula. You may refer to the full Actionscript under Reaction1.as.

Step 3: An Interactive Version

Take note that this reflection formula is applicable to line of any gradient. In fact, you can program your line to be adjustable at runtime and see it reflecting circles like the Flash presentation below. Just click and drag near the lower end of the to redefine it.

Step 4: Sliding Along Line

The concept of sliding along the line is almost identical to reflection. Observe the diagram below.

The vector of slide is A' = A + V(Ap) with V(Ap) representing a vector with magnitude of Ap. Again, to obtain Ap we shall project A onto the left normal.

Note that as the circle is sliding along the line, it is colliding with the line. Of course, collision points differ among circles that collide onto line, so some overlap the line as they move along it. This doesn’t look good, so we’ll have to reposition them.

Step 5: Redefine Location

Now, let’s reposition circles on the line while maintaining their contact with line. Refer to the diagram below.

An important variable to calculate is the projection of A along line. The radius of circle is readily available, and we already have B, so we can form the vectors of B and C. Adding the two will give us A, the exact location to reposition circle. Simple!

The Flash presentation below is coded according to the mentioned idea. But there is one problem: the circles jitter along the line.

There’s one final detail we missed. Diagram above shows magnitude of C should be equivalent to radius of circle. However, this will position circle back above the line. Since there’s no collision detected there, the circle will fall onto the line again, which in turn will flag the collision detection and cause the circle to be repositioned.

This cycle will repeat until the is past the end of the line segment; the visual result of this cycle is the jittering effect.

The solution to this problem is to set the magnitude of C to slightly less than the radius of the circle: (radius of circle - 1), say. Observe the Flash demo below which uses this idea:

Step 6: Implementation

So here’s the important ActionScript snippet for sliding along the line. I’ve highlighted the important parts.

Conclusion

In this tutorial I will introduce you to FZip, an AS3 Library that lets you open zip files inside your Flash projects. This can save a lot of bandwidth; in this tutorial we will load an 2.5MB zip file which contains 9.3MB worth of assets.

Final Result Preview

Let’s take a look at the final result we will be working towards. Click here to open a SWF that will in turn load a zip file full of images, and display them in a tiled grid.

(The blurring visible on some icons is due to Flash automatically attempting to scale them up to 32x32px, even though those particular images are 16x16px.)

Here we create a new instance of the FZip class, add two event listeners, and load our zip file. Last, we set imageTileList to be invisible (We don’t want it to show until all the images from the zip have loaded).

Step 8: onOpen()

Add the following new function beneath the setupFzip() function you entered above:

Since this is running every frame, we’ll place an artificial restriction on the number of files within the archive that we deal with at once. That’s the purpose of the for-loop.

zip.getFileCount() reveals how many files are in the zip; numFiles stores how many files we’ve dealt with so far. So, line 5 checks whether there are still more files to deal with.

If there aren’t any files left, we skip to line 17 and just do some basic clearup: remove the ENTER_FRAME listener, remove the “loading” text field , make the tile list visible, and link it to the data.

If there are files left, we get the next one in our list using numFiles as an index. We then check whether it’s a PNG from the icons folder; since we know the structure of the zip beforehand, we can cheat and just check whether the file’s name and path contains “woofunction-icons” and “.png”.

To get the image from the zip and into a DisplayObject, we can use a Loader. This class is often used to load an image from a URL, but here we’re using its loadBytes() method to get the data from the ByteArray created by FZip.

Since Loader extends DisplayObject, we can just add it straight to the TileList’s DataProvider. Then we increment both numFilesLoaded and numFiles.

Why do we have two integers to keep track of how many files are loaded? Well, numFiles keeps count of all the files we’ve examined from the zip, whereas numFilesLoaded keeps count specifically of the image files that we’ve loaded into the DataProvider. It’s the latter variable that we use to update the “loading” text at the end of the function.

Conclusion

FZIP is an amazing little utility to save some loading time and bandwidth. I hope you’ve found this tutorial useful, and thanks for reading!

Building real time networked games and applications can be challenging. This tutorial will show you how to connect flash clients using Cirrus, and introduce you to some vital techniques.

Premium Preview

Click the start button in the SWF above to create a ‘sending’ version of the application. Open this tutorial again in a second browser window, copy the nearId from the first window into the textbox, and then click Start to create a ‘receiving’ version of the application.

In the ‘receiving’ version, you’ll see two rotating needles: one red, one blue. The blue needle is rotating of its own accord, at a steady rate of 90°/second. The red needle rotates to match the angle sent out by the ‘sending’ version.

(If the red needle seems particularly laggy, try moving the browser windows so that you can see both SWFs at once. Flash Player runs EnterFrame events at a much lower rate when the browser window is in the background, so the ‘sending’ window transmits the new angle much less frequently.)

Read the Full Tutorial

Tuts+ Premium Membership

We run a Premium membership system which periodically gives members access to extra tutorials, like this one! You’ll also get access to Psd Premium, Vector Premium, Audio Premium, Net Premium, Ae Premium, Cg Premium, Photo Premium, and the new Mobile Premium too. If you’re a Premium member, you can log in and download the tutorial. If you’re not a member, you can of course join today!

Building a button from a bitmap can be bothersome. If you’re using the Flash IDE, you can create a mask to determine which pixels are part of the button and which aren’t, but in any other workflow, the entire rectangle containing the bitmap – including any transparent pixels – will be clickable. In this tutorial, you’ll learn how to automatically make all transparent pixels unclickable, with just a few lines of code.

Final Result Preview

Let’s take a look at the final result we will be working towards:

Notice that the hand cursor only appears when hovering over the actual image; even the gaps in the hair don’t cause it to appear. And it’s not just for show: the button presses only register when clicking on these areas.

Introduction: What’s So Special?

At a first glance, the SWF above appears extremely simple. But look closer! Notice how in the demo above, a button press is only counted if you click somewhere on the actual image. This isn’t what would normally happen. Since a bitmap image is always a rectangle, clicking anywhere inside its rectangle normally would count as a button press. Take a look at the example below, where I have outlined the boundary rectangle of our image. Here, you can click anywhere inside the rectangle, including the transparent areas.

As you can see, this is not what we want! For starters, a user could accidentally click the button when he doesn’t mean to. In addition, it looks strange when a hand cursor appears over blank space. In this tutorial, you’ll learn how to easily correct these problems.

Step 1: Getting Started

Open up FlashDevelop and create a new AS3 project (Project > New Project) and call it something like BitmapButtonProj. On the right, open up the src folder and double-click Main.as to open it. Add a new class to your project (right-click /src/ > Add > New Class) called BitmapButton

Step 2: Embedding an Image

We now need an image to work with. Here is the one I’m using:

To use a bitmap image (such as a .jpeg file or a .png file) in Actionscript 3, we have to embed it. FlashDevelop makes this easy. After saving the above image somewhere, right-click the lib folder on the right, mouse over Add, and select the Library Asset option.

If you want to use your own image, be sure to select one with transparency.

The image you selected will now appear in the lib folder in FlashDevelop. Right-click the image and select Generate Embed Code.

This code embeds the image in to our project. Whenever you embed an image, you need to define on the next line a class that represents the image you embedded. In this case, our class is called ButtonImg.

Step 3: Adding a TextField

Next, we’ll add a TextField to display how many times we have clicked the button (which will be added next). Add this to Main():

When we instantiate our BitmapButton in line 36, we pass our embedded image class as a parameter. This will be used by the BitmapButton class. After this, we can simply treat our BitmapButton instance like any other DisplayObject: we can position it and add a MouseEvent.CLICK listener as we normally would.

Step 7: The MOUSE_MOVE Event Listener

Our simple looking MOUSE_MOVE event listener is the real brains behind our class. Its main purpose is to determine whether the mouse cursor is over a transparent pixel or not. Let’s look at how it does this.

The getPixel32() Function

The first line gets the color and transparency of the pixel that the cursor is currently over. To do this, we use the getPixel32() method of the variable bitmapData (which, remember, is the bitmap data representation of our image).

We must pass an x- and y-coordinate to getPixel32(), so naturally we use the mouse’s position.

The call then returns a uint representing the color and transparency of the pixel at the location we supplied.

Colors in Flash are normally treated as a hexadecimaluint in the format RRGGBB. The first two digits represent the amount of red in the color, the next two, green, and the final two, blue. However, getPixel32() provides us with a special uint representing our pixel in the format AARRGGBB. Here, the first two digits represent the alpha, or the amount of transparency, from 00 (clear) to FF (opaque).

So, for example, FF980000 would represent a fully opaque red color, while 00980000 would represent a fully transparent red color. You’ll typically see these represented as 0xFF980000 or 0x0098000: the “0x” lets you (and Flash!) know that the number is in hexidecimal (0-f), rather than decimal (0-9).

The Bitwise Unsigned Right Shift Operator

At this point, we have a uint called pixel which is holding the color and alpha of the pixel beneath our mouse in the AARRGGBB format. Unfortunately, this is too much information. All we care about is the transparency of this pixel, or the AA part.

You could write a mathematical expression to obtain this section – in fact, int(pixel/Math.pow(16,6)) would work. This is a somewhat awkward statement, though, and slower performance-wise than another option we have: the bitwise unsigned right shift operator, >>>.

Our variable pixel is just a binary number to Flash. We normally write it in hexadecimal just to make it more readable. Without going into too much detail, every digit of a hexadecimal number can be represented by a string of four binary digits, each one either a 0 or a 1. (So, hexadecimal uses digits 0-f, decimal uses 0-9, and binary uses 0-1.)

Say we have a hexadecimal number, D4. In binary, this would be represented as 11010100. Notice how we use eight binary digits for the binary representation: four times as many as in hexadecimal.

With this is mind, let’s examine what the >>> operator actually does. Lets use our previous example, the hexadecimal number D4, or 0xD4 for clarity. Now let’s use >>> as so:

0xD4 >>> 4

Notice that 4 is a normal decimal representation of a number (there’s no “0x” at the start). This expression essentially shifts every binary digit in D4 four places to the right, and forgets about any digit that would go off the end of the number.

0xD4, in binary, is 11010100. Apply four shifts, and it becomes 1101. In hexadecimal, this is 0xD.

If you’re having trouble understanding this, imagine the binary digits as blocks sitting at the right side of a table. The >>> operator is just like pushing the blocks to the right. Here’s our original binary number:

Now here’s our new number, after we do 0xD4 >>> 4 :

Notice how after we shifted 0xD4 by 4 bits, we ended up with just 0xD? That’s not a coincidence. As said before, each hexadecimal digit is made up of 4 binary digits – so, each time we shift it to the right by 4, we essentially knock one hexadecimal digit off the end. You can probably see where we are going with this!

Back to our pixel, in 0xAARRGGBB format. If we shift it by 24, we are actually shifting by 6 hexadecimal digits. This means the RRGGBB portion gets knocked off, and we end up with just the 0xAA part left, which is our alpha component.

A quick numerical example: Say our pixel is equal to FF980000. In binary, this is 1111 1111 1001 1000 0000 0000 0000 0000. (Each group of 4 digits represents one hexadecimal digit.) When we shift this by 24, we simply end up with 1111 1111, or FF, our two transparency digits.

Take a look at it again:

useHandCursor = buttonMode = ((pixel >>> 24) > THRESHOLD);

Okay, the (pixel >>> 24) part makes sense now, but what about the rest?

It’s easy. We check whether our alpha component (the result of pixel >>> 24) is greater than the value of THRESHOLD (which is currently set to 0). If it is, useHandCursor and buttonMode are set to true, which will make the cursor change to a hand. This makes our image seem like a button.

If our alpha component is less than or equal to THRESHOLD, the cursor will remain normal, since the mouse is over a (semi-)transparent pixel. Since we have it set to 0, only fully transparent pixels will not be included as part of our button, but you could set this to, say, 0×80, and then it would display the hand cursor for anything that’s more than half transparent.

Step 8: The CLICK Event Listener

The final part of our BitmapButton class is the MouseEvent.CLICK event listener. This function will be called every time our image is clicked, no matter whether that pixel is transparent or not. (Changing the mouse cursor as we did before will not affect the actual MouseEvent.)

So, every time there is a click, we check the useHandCursor property. If it is true, this means the mouse is over a normal pixel in our image, and we don’t need to do anything. This makes sense – the event will then continue on to the event listener we added in Main.as. However, if useHandCursor is false, we have to do something to stop the event from continuing on to other event listeners.

For this, we use the stopImmediatePropagation() method that all Event objects have. Simply put, this stops the flow of the event, and no more event listeners will receive it. So, our event listener function in Main.as will never be called.

Warning: this could have a nasty side effect – any global event listener will not get the event either. If you are worried about this, you can try adding the line parent.dispatchEvent(e.clone()); after e.stopImmediatePropogation(). While this is beyond the scope of the tutorial, I recommend reading more about the event system here.

Conclusion

This wraps up our tutorial! Thanks for reading, and I hope you have learned something new.

A note of caution when using our BitmapButton class – other MouseEvents will still work as normal, since we only dealt with MouseEvent.CLICK. If you wanted, you could use the same technique we used for MouseEvent.CLICK and apply it to other events, such as MouseEvent.MOUSE_DOWN.

Our BitmapButton class allows us to quickly and easily make great buttons from bitmap images with transparency, as we did in this demo. If you have any questions, I’ll be glad to answer them, just leave a comment below.

Are you looking to start your new year with a fresh set of prints to help promote your design business? Today, our friends at UPrinting are kicking off 2012 by giving away business cards, posters, or postcards to 36 lucky Tuts+ readers. To enter, all you have to do is submit your entry using the form below and select which prize you would prefer.

Update: The winners for this giveaway have been selected. Thanks to everyone who participated.

If you are a frequent reader of our site, chances are, you are already familiar with UPrinting. They are an online printer that offers business cards, poster printing, postcard printing, and much more. UPrinting is a frequent sponsor of this site and we are very excited to partner with them on another giveaway.

Hey there and welcome to "Flash Video Training Source", a resource for anybody interested in learning more about Adobe's great tool. We feature educational videos, which will help you master Adobe Flash and help you get to know all of its features. We at "Flash Video Training Source" believe that video training and video... more

Why don't you follow us on Twitter and get the latest video tutorials twitted to your account. Just click on the floating twitter bar to your right!