By Zevan | September 15, 2009
Here is a quick list of the new features in QuickBox2D along with links to the docs.
1) The QuickBox2D.STEP event:
A few releases ago, frim (frame rate independent motion) was added to QuickBox2D. However, there was no way to execute calls to b2Body.ApplyImpulse() b2Body.SetLinearVelocity() etc… along with the b2World.Step() method. This meant that you couldn’t call these methods in a way that would truly maintain frim. As you’ll see in upcoming demos, rather than doing key controls or additional simulation logic in an enterframe event, I’ll be listening for the QuickBox2D.STEP event. This is executed every time a timeStep occurs. If frim is on, this the STEP event will be executed independently of frameRate.
2) Some features were added to help trigger events at specific times in the simulation. See:
QuickBox2D.totalTimeSteps
QuickBox2D.addTimeStepSequence
…for an example of addTimeStepSequence() check out this recent post.
3) Some additional control was added to mouse dragging for QuickBox2D. There is a new property in the QuickBox2D params object called customMouse. When set to true, this enables you to pass in mouse coordinates rather than having QuickBox2D automatically use the coordinates of the DisplayObject that all the rigid bodies are being drawn to. This feature is useful if you are rendering using a 3D engine. See:
QuickBox2D customMouse
QuickBox2D.setMouse()
4) A few features were added to make contact points easy to work with. See:
QuickBox2D.addContactListener()
QuickContacts
…I’ll be posting a few demos showing how to use QuickContacts - here are the first two (more to come in the next few days):
part 1
part 2
By Zevan | September 15, 2009
Actionscript:
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import com.actionsnippet.qbox.*;
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[SWF(width = 800, height = 600, backgroundColor = 0x000000, frameRate=60)]
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var sim:QuickBox2D = new QuickBox2D(this);
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sim.createStageWalls();
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var boxA:QuickObject = sim.addBox({x:3, y:3, width:2, height:2});
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var boxB:QuickObject = sim.addBox({x:3, y:6, width:2, height:2});
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// add a few extra circles to show that there are other contacts
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// occuring
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for (var i:int = 0; i<10; i++){
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sim.addCircle({x:5 + i, y:4, radius:0.1 + Math.random()});
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}
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sim.start();
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sim.mouseDrag();
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// when boxA touches boxB change their alpha values to 50%
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var contacts:QuickContacts = sim.addContactListener();
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contacts.addEventListener(QuickContacts.ADD, onAdd);
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contacts.addEventListener(QuickContacts.PERSIST, onPersist);
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contacts.addEventListener(QuickContacts.REMOVE, onRemove);
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function onAdd(evt:Event):void{
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if(contacts.isCurrentContact(boxA, boxB)){
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boxA.userData.alpha = 0.5;
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boxB.userData.alpha = 0.5;
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}
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}
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function onPersist(evt:Event):void{
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if(contacts.isCurrentContact(boxA, boxB)){
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boxA.userData.alpha = 0.5;
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boxB.userData.alpha = 0.5;
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}
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}
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function onRemove(evt:Event):void{
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if(contacts.isCurrentContact(boxA, boxB)){
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boxA.userData.alpha = 1;
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boxB.userData.alpha = 1;
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}
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}
Note: This snippet requires QuickBox2D 1.0 or greater
This is another example showing how to make use of QuickBox2D contacts. In this example three contact events are used ADD, PERSIST and REMOVE. When the two boxes are touching their alpha values are set to 50% - otherwise their alpha values are at 100%.
Have a look at the swf...
A Little Detail About the Events
The ADD event is dispatched when a new b2ContactPoint is generated. The PERSIST event is dispatched as long as the b2ContactPoint exists for more than one timeStep - and from what I can tell, is dispatched until the rigid bodies it is associated with go to sleep. The REMOVE event is called when the b2ContactPoint is removed, meaning the rigid bodies that caused the creating of the b2ContactPoint are no longer touching.
You need to be careful with the code that you place inside the listener functions for these events. The reason being that these events are called many many times for every contact point in the simulation.
By Zevan | September 14, 2009
Actionscript:
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import com.actionsnippet.qbox.*;
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import Box2D.Common.Math.*;
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[SWF(width = 800, height = 600, backgroundColor = 0x000000, frameRate=60)]
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var sim:QuickBox2D = new QuickBox2D(this, {debug:false, frim:true});
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sim.createStageWalls();
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var boxA:QuickObject = sim.addBox({x:3, y:3, width:2, height:2, fillColor:0xFF0000});
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var boxB:QuickObject = sim.addBox({x:3, y:6, width:2, height:2, fillColor:0xFF0000});
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sim.start();
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sim.mouseDrag();
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// when boxA touches boxB a circle QuickObject is created
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var contacts:QuickContacts = sim.addContactListener();
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// listen for contact points being added
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contacts.addEventListener(QuickContacts.ADD, onAdd);
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function onAdd(evt:Event):void{
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// see if this contact event is associated with boxA and boxB
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if(contacts.isCurrentContact(boxA, boxB)){
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// get the location of the collision in world space
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var loc:b2Vec2 = contacts.currentPoint.position;
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// you cannot create new QuickObjects inside this listener function
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// so we just give a 5 ms delay
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setTimeout(sim.addCircle, 5, {x:loc.x, y:loc.y});
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}
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}
Note: This snippet requires QuickBox2D 1.0 or greater
I've created a few simple examples to show how to use QuickBox2D contact listeners. This is the first one. When two boxes collide circles are added to the simulation at the point of collision.
Have a look at the swf...
By Zevan | September 14, 2009
QuickBox2D 1.0 is ready. It contains a bunch of small bug fixes and a few new features that I'll be demoing in the next few posts. The main new features relate to collision detection and simple event sequencing.
Go download it from here...
I also spent some time updating the docs.... everything is documented... I may add additional documentation text over the next few days...
A detailed tutorial for QuickBox2D is also in the works...
[EDIT]
Also, if you find any bugs send me an e-mail (see about page for e-mail)... if there are any bugs left I'd like to fix the asap.... You can also feel free to e-mail any API suggestions...