Check out part 2 RIGHT HERE
What’s up? Ready to learn a little something about QuickBox2D? Wait, you don’t know what QuickBox2D is? Well, QuickBox2D is a simpler way of using Box2D — A physics library originally written in C++ and ported to many other platforms including AS3 — and is much cleaner and easier to use than the straight Box2D library. Anyways, QuickBox2D was made by Zevan Rosser, who is a teacher at the School of Visual Arts in NYC. You can see a lot of great examples of how to use QuickBox2D at his blog, ActionSnippet.
Let’s get started here. First thing you need to do is get the latest version of Box2D and QuickBox2D at these links:
Box2DFlashAS3
QuickBox2D
And Save them in a new folder called ‘PhysicsPlatformer’.
Now open Flash CS3/4 and create a new Flash AS3 Document File. Go back to the File menu button and add another file, this time we are going to add an Actionscript Document (.as file). Save the .fla as game.fla, and save the .as file as global.as.
The global.as file is going to contain one variable (kind of a waste, I know, but it can be useful when you expand your engine a little bit more, like for implementing wall-jumping, it could be useful). Since global.as is the smallest, we’ll start with that. This is the code that should be in your global.as class file:
package {
public class global {
public static var grounded:Boolean = false;
public function global():void {
}
}
}
The important thing to notice here is ‘static’ on line 5. When you use the word static in the definition of a variable, it means that you can access the variable by stating the class name then the variable name without instantiating the class. This is really great because when we need to access our boolean, grounded, all we type is “global.grounded”.
The next part is probably the hardest part to do, actually making the engine. When I was in works of creating the engine, I had some real trouble getting the main character (a ball in our case) to stay still on a slope, and i came up with an ingenious way of fixing this problem, and you’ll see in the tutorial here how I did it.
Lets start by setting up our QuickBox2D simulation:
import com.actionsnippet.qbox.*;
var sim:QuickBox2D = new QuickBox2D(this);
sim.setDefault({lineAlpha:0, fillColor:0x333333});
sim.createStageWalls();
sim.start();
If you paste this in the timeline of game.fla and test it, you should see a dark grey box surrounding your stage, If not, then look through your code checking for typos or something because we have a long way to go.
Next we can add our character, a simple ball will do:
import com.actionsnippet.qbox.*;
var sim:QuickBox2D = new QuickBox2D(this);
sim.setDefault({lineAlpha:0, fillColor:0x333333});
sim.createStageWalls();
var main:QuickObject = sim.addCircle({x:3, y:3, restitution:0, lineAlpha:1, fillColor:0x888888, allowSleep:false, fixedRotation:true});
sim.start();
There is obviously only one addition to this, it’s on line 7. First we make a new variable that’s typcasted as a QuickObject, then we set it equal to the results of the addCircle function. You’ll notice in the function that there is one argument, and it’s an object with a lot of stuff in it. I’ll point out the most important parts of those parameters. allowSleeping: false. If our object could ‘sleep’ then we would not be able to move it unless we wake it up, I suppose it’s fine to leave this as true (by default) and then whenever you want to move the character wake it up, but it’s not making the hugest impact on the game right now, so don’t worry about it. And, fixedRotation: true. Let’s say we are controlling our circle and we get to a slope, and we are trucking up the slope, but then we have to stop for a second because a friend is calling or something, when we let go of our keys, the ball will just start rolling down the slope, and we can’t have that.
So, great, we have a ball. How do we move it? We move the ball by adjusting it’s linear velocity. But first we have to set up a few functions to handle our keyboard input and such:
import com.actionsnippet.qbox.*;
import Box2D.Common.Math.*
var sim:QuickBox2D = new QuickBox2D(this);
sim.setDefault({lineAlpha:0, fillColor:0x333333});
sim.createStageWalls();
var main:QuickObject = sim.addCircle({x:3, y:3, restitution:0, lineAlpha:1, fillColor:0x888888, allowSleep:false, fixedRotation:true});
sim.start();
stage.addEventListener(Event.ENTER_FRAME, loop);
stage.addEventListener(KeyboardEvent.KEY_UP, checkKeysUp);
stage.addEventListener(KeyboardEvent.KEY_DOWN, checkKeysDown);
var keyArray:Array = new Array();
var speed:int = 5;
for (var i=0; i<222; i++) {
keyArray.push(false);
}
function loop(e:Event):void {
if(keyisdown(39)){
main.body.SetLinearVelocity(new b2Vec2(speed, main.body.GetLinearVelocity().y));
}
if(keyisdown(37)){
main.body.SetLinearVelocity(new b2Vec2(-speed, main.body.GetLinearVelocity().y));
}
}
function checkKeysDown(event:KeyboardEvent):void {
keyArray[event.keyCode]=true;
}
function checkKeysUp(event:KeyboardEvent):void {
keyArray[event.keyCode]=false;
}
function keyisdown(X:Number):Boolean {
return keyArray[X];
}
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