Random Negative or Positive

By Zevan | June 17, 2009
CLICK HERE TO COPY
Actionscript:
  1. for (var i:int = 0; i<10; i++){
  2.   // randomly set a variable to -1 or positive 1
  3.   trace(int(Math.random()*2) - 1 | 1);
  4. }
  5.  
  6. /* outputs something like this
  7. 1
  8. 1
  9. -1
  10. 1
  11. -1
  12. -1
  13. 1
  14. 1
  15. -1
  16. -1
  17. */

The past few days I found myself using this one-liner a few times. Just a quick way to randomly get -1 or 1.

I was brainstorming today and wrote a weird/bad inline version of an old post:

var rand:Number = [-3, 2, 1, 1, 1, 0.5][int(Math.random() * 6)];

I need to install a related posts plugin for WordPress - would be nice if this post were related to my old post about Tausworthe random seeds.

Been posting medium/large snippets and snippets the relate to QuickBox2D - so today I figured I'd get back to basics...

Posted in one-liners, random | Tagged , , | 3 Comments

QuickBox2D FRIM

By Zevan | June 15, 2009
CLICK HERE TO COPY
Actionscript:
  1. import com.actionsnippet.qbox.*;
  2. import Box2D.Common.Math.*;
  3.  
  4. // try altering your frame rate
  5. [SWF(backgroundColor=0x000000, width=700, height=600, frameRate=30)]
  6. // try setting frim to false
  7. var sim:QuickBox2D = new QuickBox2D(this, {iterations:20, timeStep:1 / 60, frim:true});
  8.  
  9. sim.setDefault({fillColor:0x003366, lineAlpha:0});
  10. sim.createStageWalls();
  11.  
  12. sim.addBox({x:10, y:18, height:3, density:0});
  13.  
  14. sim.setDefault({fillColor:0x004466, lineColor:0x2B80F5});
  15.  
  16. var cVel:b2Vec2 = new b2Vec2();
  17.  
  18. for (var i:int = 0; i<32; i++){
  19.     var c:QuickObject = sim.addCircle({x:13 + i % 8, y:10 + int(i / 8), friction:0.01, radius:0.2 + Math.random()*0.3, angularDamping:1});
  20.     cVel.x = Math.random() * 4 - 2;
  21.     cVel.y = Math.random() * 4 - 2;
  22.     c.body.SetLinearVelocity(cVel);
  23. }
  24.  
  25. var box:QuickObject = sim.addBox({x:3, y:16, width:2, height: 2});
  26. var boxVel:b2Vec2 = new b2Vec2(15, -25);
  27.  
  28. sim.start();
  29.  
  30. // shoot the box from left to right
  31. setTimeout(positionBox, 200);
  32. function positionBox():void{
  33.     // reset box position
  34.     box.x = 3, box.y = 16;
  35.     setTimeout(shootBox, 500);
  36. }
  37. function shootBox():void{
  38.     box.body.SetLinearVelocity(boxVel);
  39.     box.body.SetAngularVelocity(10);
  40.     // shoot the box again
  41.     setTimeout(positionBox, 4000);
  42. }

You'll need to download the latest version of QuickBox2D in order to run this snippet (alpha 107 as of this post). I recommend checking out the demo below first though...

The most notable feature of this release is FRIM (frame rate independent motion). FRIM is used to attempt to keep the speed of the Box2D simulation constant no matter what frame rate the swf is running at. This is good because frame rates will vary from browser to browser and from computer to computer.

Mr.Doob suggested that I implement this feature in QuickBox2D. If you haven't seen his site I highly recommend checking it out - really great stuff there.

I created a demo to illustrate the FRIM feature... this demo is basically the same as the above snippet with a few extra buttons added to control frame rate and toggle FRIM.


Take a look at the demo here...

While this new feature seems to be working, I believe there still may be room for improvement. Please let me know if the demo doesn't work correctly on your machine. As of now, I've only tested it on my 2.5 Ghz Intel Core 2 Duo.

Also, any suggestions to improve the clarity of this demo are appreciated... I found it kind of hard to think of a good demo to show FRIM in action. The original demo really didn't make much sense... so I gave Rich Shupe a call and he helped me come up with the idea for the current demo.

UPDATE:
I just updated the demo so that the simulation restarts when you change the frame rate (as per Mr.doob's suggestion below)

Posted in Box2D, QuickBox2D, motion | Tagged , , , , | 10 Comments

QuickBox2D w/ Key Controls

By Zevan | June 15, 2009
CLICK HERE TO COPY
Actionscript:
  1. import com.actionsnippet.qbox.*;
  2. import Box2D.Common.Math.*
  3.  
  4. [SWF(backgroundColor=0xEFEFEF, width=700, height=600, frameRate=60)]
  5.  
  6. var sim:QuickBox2D = new QuickBox2D(this);
  7.  
  8. sim.setDefault({lineColor:0xCC0000, fillColor:0xCC0000});
  9.  
  10. // create compound shape (two circles and a box for the character)
  11. var charParts:Array = [];
  12. // x and y position are now relative to center of compound shape
  13. charParts[0] = sim.addBox({x:0, y:0, width:1, height:2});
  14. charParts[1] = sim.addCircle({x:0, y:-1, radius:0.5});
  15. charParts[2] = sim.addCircle({x:0, y:1, radius:0.5});
  16. var char:QuickObject = sim.addGroup({objects:charParts, x:2, y:2.5, allowSleep:false, angularDamping:0.8, linearDamping:1.5});
  17.  
  18. // vector for linear velocity of character
  19. var charVel:b2Vec2 = new b2Vec2();
  20.  
  21. // angular velocity of character
  22. var charVelAng:Number = 1;
  23. char.body.SetAngularVelocity(charVelAng);
  24.  
  25. // world/platforms
  26. sim.setDefault({lineColor:0x666666, fillColor:0x666666, height:0.5, density:0});
  27. sim.createStageWalls();
  28. sim.addBox({x:3, y:5, width:5});
  29. sim.addBox({x:11, y:5, width:5});
  30. sim.addBox({x:8, y:9, width:8});
  31. sim.addBox({x:4, y:13, width:8});
  32. sim.addCircle({x:16, y:8, radius:2});
  33. sim.addCircle({x:12, y:15, radius:2});
  34.  
  35. // falling circles
  36. sim.setDefault({lineColor:0x2870B5, fillColor:0x2870B5});
  37. for (var i:int = 0; i<15; i++){
  38.     sim.addCircle({x:5 + i, y:2, radius:0.25 ,density:1});
  39. }
  40.  
  41. sim.start();
  42.  
  43. // key controls
  44. addEventListener(Event.ENTER_FRAME, onLoop);
  45. function onLoop(evt:Event):void {
  46.     charVel = char.body.GetLinearVelocity();
  47.     charVelAng =  char.body.GetAngularVelocity();
  48.    
  49.     if (key[Keyboard.RIGHT]){
  50.         charVel.x += 1
  51.         char.body.SetLinearVelocity(charVel);
  52.        
  53.         charVelAng += 1;
  54.         char.body.SetAngularVelocity(charVelAng);
  55.     }
  56.     if (key[Keyboard.LEFT]){
  57.         charVel.x -=1;
  58.         char.body.SetLinearVelocity(charVel);
  59.        
  60.         charVelAng -= 1;
  61.         char.body.SetAngularVelocity(charVelAng);
  62.     }
  63.     if (key[Keyboard.UP]){
  64.          charVel.y = -10;
  65.          char.body.SetLinearVelocity(charVel);
  66.            
  67.          charVelAng *= 0.8;
  68.          char.body.SetAngularVelocity(charVelAng);
  69.     }
  70. }
  71. // basic key setup
  72. var key:Object = new Object();
  73. stage.addEventListener(KeyboardEvent.KEY_DOWN, onKeyPressed);
  74. stage.addEventListener(KeyboardEvent.KEY_UP, onKeyReleased);
  75. function onKeyPressed(evt:KeyboardEvent):void {
  76.     key[evt.keyCode] = true;
  77.     key.keyCode = evt.keyCode;
  78. }
  79. function onKeyReleased(evt:KeyboardEvent):void { key[evt.keyCode] = false}

This snippet shows one way to go about doing key controls using QuickBox2D

Take a look at the swf here...

This works with the current version of QuickBox2D.... tomorrow I'll be uploading the new version of QuickBox2D which supports FRIM (frame rate independent motion) and contains a few additional minor tweaks and fixes.

Posted in Box2D, QuickBox2D, keys, motion | Tagged , , , | 1 Comment

x and y Coordinates in 1D Array / Vector

By Zevan | June 14, 2009
CLICK HERE TO COPY
Actionscript:
  1. var canvas:BitmapData=new BitmapData(400,400,false,0x000000);
  2. addChild(new Bitmap(canvas));
  3. var pix:Vector.<uint>=canvas.getVector(canvas.rect);
  4.  
  5. canvas.lock();
  6. for (var i:int = 0; i<300; i++) {
  7.     var xp:int=50+i;
  8.     var yp:int=50+i/2;
  9.     // target x and y coords in 1D array
  10.     pix[xp+yp*400]=0xFFFFFF;
  11. }
  12. canvas.setVector(canvas.rect, pix);
  13. canvas.unlock();

This snippet shows how to target x and y coordinates in a 1D Array / Vector. This can be useful sometimes when working with setVector().

This is sort of like re-inventing setPixel().... and for that reason is kind of pointless - that said, it's interesting to know. I first learned about this technique from using processing.

Posted in BitmapData, Vector, arrays, pixel manipulation, setPixel | Tagged , , | Leave a comment