Tag Archives: actionscript

Circle of Particles #2

By Zevan | March 18, 2009
CLICK HERE TO COPY
Actionscript:
  1. [SWF(width = 400, height = 400)];
  2. var canvas:BitmapData = new BitmapData(400,400, false, 0x000000);
  3. var eraser:BitmapData = new BitmapData(400,400, true, 0x11000000);
  4. addChild(new Bitmap(canvas));
  5.  
  6. var particles:Array = new Array();
  7. for (var i:int = 0; i <500; i++){
  8.     particles.push(makeParticle());
  9. }
  10.  
  11. addEventListener(Event.ENTER_FRAME, onLoop);
  12. function onLoop(evt:Event):void {
  13.     canvas.copyPixels(eraser, eraser.rect, new Point(0,0), null, null, true);
  14.     for (var i:int = 0; i <particles.length; i++){
  15.         particles[i]();
  16.     }
  17. }
  18.  
  19. function makeParticle():Function {
  20.     var dx:Number, dy:Number;
  21.     var x:Number = 200;
  22.     var y:Number = 200;
  23.     var vx:Number = Math.random() * 4 - 2;
  24.     var vy:Number = Math.random() * 4 - 2;
  25.     var ang:Number;
  26.     return function():void {
  27.               x += vx;
  28.               y += vy;
  29.               dx = 200 - x;
  30.               dy=  200 - y;
  31.                if (Math.sqrt((dx * dx) + (dy * dy))> 130){
  32.                 ang = Math.atan2(dy, dx) / Math.PI * 180;
  33.                  vx = Math.cos(ang);
  34.                  vy = Math.sin(ang);
  35.                }
  36.                canvas.setPixel(x, y, 0xFFFFFF);
  37.     }
  38. }

This is an interesting variation on yesterdays post. The result will looks like this...


Click to view swf...

I also decided to do a processing port of this with 3,000 particles:

Processing Version

The processing version eventually evolved into this:


Click for enlarged version...

Posted in BitmapData, motion, setPixel | Also tagged , | 2 Comments

Circle of Particles

By Zevan | March 17, 2009
CLICK HERE TO COPY
Actionscript:
  1. var canvas:BitmapData = new BitmapData(400,400, false, 0xFFFFFF);
  2. addChild(new Bitmap(canvas));
  3. var eraser:BitmapData = new BitmapData(400,400, true, 0x33FFFFFF);
  4.  
  5. var particles:Array = new Array();
  6. for (var i:int = 0; i <1000; i++){
  7.     particles.push(makeParticle());
  8. }
  9.  
  10. addEventListener(Event.ENTER_FRAME, onLoop);
  11. function onLoop(evt:Event):void {
  12.     canvas.copyPixels(eraser, eraser.rect, new Point(0,0), null, null, true);
  13.     for (var i:int = 0; i <particles.length; i++){
  14.         particles[i]();
  15.     }
  16. }
  17.  
  18. function makeParticle():Function {
  19.     var dx:Number, dy:Number;
  20.     var x:Number = 200;
  21.     var y:Number = 200;
  22.     var vx:Number = Math.random() * 4 - 2;
  23.     var vy:Number = Math.random() * 4 - 2;
  24.     return function():void {
  25.               x += vx;
  26.               y += vy;
  27.               dx = x - 200;
  28.               dy= y - 200;
  29.                if (Math.sqrt((dx * dx) + (dy * dy))> 100){
  30.                  vx *= -1;
  31.                  vy *= -1;
  32.                }
  33.                canvas.setPixel(x, y, 0x000000);
  34.     }
  35. }

This creates a circular area filled with moving particles/pixels. It makes use of yesterdays functional programming techniques.

Posted in BitmapData, functions, motion, setPixel | Also tagged | Leave a comment

Functional Pseudo-Objects

By Zevan | March 16, 2009
CLICK HERE TO COPY
Actionscript:
  1. var moverNum:int = 40;
  2. var movers:Array = new Array();
  3.  
  4. for (var i:int = 0; i<moverNum; i++){
  5.     movers.push(makeMover());
  6. }
  7.  
  8. addEventListener(Event.ENTER_FRAME, onLoop);
  9. function onLoop(evt:Event):void {
  10.     for (var i:int = 0; i<moverNum; i++){
  11.         movers[i]();
  12.     }
  13. }
  14.  
  15. function makeMover():Function{
  16.     // mover vars & setup
  17.     var xVel:Number = Math.random() * 5 + 1;
  18.     var right:Number = stage.stageWidth + 30;
  19.     var s:Shape = Shape(addChild(new Shape()));
  20.     with(s.graphics) beginFill(0xFF0000), drawCircle(0,0,5);
  21.     s.x = Math.random() * stage.stageWidth;
  22.     s.y = Math.random() * stage.stageHeight;
  23.     // return a "run" function
  24.     return function():void {
  25.          s.x += xVel;
  26.          if (s.x> right){
  27.             s.x = -30;
  28.          }
  29.     }
  30. }

This snippet creates 40 shapes that move to the right at a random velocity. When they animate off the right hand side of the stage they return from the left.

The makeMover() function has a series of variable definitions related to the x velocity and position of a Shape. The makeMover() function then returns an anonymous function that contains some logic to move the Shape "s". The anonymous function has access to the makeMover() functions temporary variables...

On the main loop we run all of the anonymous functions - animating all the shapes by their random x velocities.

It would be interesting to write the same program using classes and test the for speed differences. My assumption is that anonymous functions are expensive, but it would still be interesting to see...

Posted in functions, motion | Also tagged | Leave a comment

Bezier Intersections (not a snippet)

By Zevan | March 15, 2009
CLICK HERE TO COPY
Actionscript:
  1. var resolution:Number = .03;
  2. var pointNum:int = Math.ceil(1 / resolution);
  3.  
  4. var bezA:Array = new Array();
  5. populateArray(bezA);
  6. var a:Sprite = dot(100, 200);
  7. var b:Sprite = dot(200, 100);
  8. var c:Sprite = dot(300, 200);
  9.  
  10. var bezB:Array = new Array();
  11. populateArray(bezB);
  12. var d:Sprite = dot(300, 100, 0xCCCC00);
  13. var e:Sprite = dot(120, 130, 0xCCCC00);
  14. var f:Sprite = dot(200, 300, 0xCCCC00);
  15.  
  16. addEventListener(Event.ENTER_FRAME, onLoop);
  17. function onLoop(evt:Event):void {
  18.       with(graphics){
  19.           clear();
  20.           lineStyle(0, 0x000000);
  21.        
  22.           // calc and draw bezier points
  23.           drawBezier(bezA, a, b, c);
  24.           drawBezier(bezB, d, e, f);
  25.          
  26.           // calc collisions
  27.           var intersections:Array = calculateIntersection(bezA, bezB);
  28.          
  29.            // draw collisions
  30.            beginFill(0xFF0000);
  31.            if (intersections.length> 0){
  32.                 for (var i:int = 0; i<intersections.length; i++){
  33.                     drawCircle(intersections[i].x, intersections[i].y, 3);
  34.                 }
  35.            }
  36.            endFill();
  37.      }
  38. }
  39.  
  40. function populateArray(a:Array):void {
  41.     for (var i:int = 0; i<pointNum; i++){
  42.         a.push(new Point());
  43.     }
  44. }
  45.  
  46. function drawBezier(bez:Array, a:Sprite, b:Sprite, c:Sprite):void{
  47.      with(graphics){
  48.          bezier(bez, a.x, a.y, b.x, b.y, c.x, c.y);
  49.          var leng:Number = bez.length;
  50.          moveTo(bez[0].x, bez[0].y);
  51.          for (var i:int = 1; i<leng; i++){
  52.              lineTo(bez[i].x, bez[i].y);
  53.          }
  54.      }
  55. }
  56.  
  57. function bezier(bez:Array, x1:Number, y1:Number, x2:Number, y2:Number, x3:Number, y3:Number):void {
  58.             var b:Number, a2:Number, ab2:Number, b2:Number;
  59.             var pnt:Point;
  60.             var inc:int = 0;
  61.             for (var a:Number = 0; a <=1; a+=resolution) {
  62.                 b= 1 - a;
  63.                 a2 = a * a;
  64.                 ab2 = a * b * 2;
  65.                 b2 = b * b;
  66.                 pnt = bez[inc];
  67.                 pnt.x = a2 * x1 + ab2 * x2  + b2 * x3;
  68.                 pnt.y = a2 * y1 + ab2 * y2 + b2 * y3;      
  69.                 inc++;
  70.             }
  71. }
  72.  
  73. function calculateIntersection(bezA:Array, bezB:Array):Array {
  74.     var intersections:Array = new Array();
  75.     var ip:Point;
  76.     var aLength:int = bezA.length;
  77.     var bLength:int = bezB.length;
  78.     var p1:Point, p2:Point, p3:Point, p4:Point;
  79.    
  80.     // compare all line segments and check for
  81.     // intersections
  82.     for (var i:int = 1; i<aLength; i++){
  83.         p1 = bezA[i - 1];
  84.         p2 = bezA[i];
  85.         for (var j:int = 1; j<bLength; j++){
  86.             p3 = bezB[j - 1];
  87.             p4 = bezB[j];
  88.             ip = intersection(p1, p2, p3, p4);
  89.             if (ip){
  90.                 intersections.push(ip.clone());
  91.             }
  92.         }
  93.     }
  94.     return intersections;
  95. }
  96.  
  97. var ip:Point = new Point();
  98.  
  99. function intersection(p1:Point, p2:Point, p3:Point, p4:Point):Point {
  100.      
  101.     var nx:Number, ny:Number, dn:Number;
  102.     var x4_x3:Number = p4.x - p3.x;
  103.     var pre2:Number = p4.y - p3.y;
  104.     var pre3:Number = p2.x - p1.x;
  105.     var pre4:Number = p2.y - p1.y;
  106.     var pre5:Number = p1.y - p3.y;
  107.     var pre6:Number = p1.x - p3.x;
  108.    
  109.     nx = x4_x3 * pre5 - pre2 * pre6;
  110.     ny = pre3 * pre5 - pre4 * pre6;
  111.     dn = pre2 * pre3 - x4_x3 * pre4;
  112.    
  113.     if (dn == 0){
  114.         return null
  115.     }
  116.     nx /= dn;
  117.     ny /= dn;
  118.     // has intersection
  119.     if(nx>= 0 && nx <= 1 && ny>= 0 && ny <= 1){
  120.         ny = p1.y + nx * pre4;
  121.         nx = p1.x + nx * pre3;
  122.         ip.x = nx;
  123.         ip.y = ny;
  124.     }else{
  125.          return null;
  126.     }
  127.     return ip
  128. }
  129.  
  130. // draggable dot
  131. function dot(xp:Number, yp:Number, col:uint = 0x507399, noDrag:Boolean = false):Sprite {
  132.     var s:Sprite = Sprite(addChild(new Sprite));
  133.     s.x = xp;
  134.     s.y = yp;
  135.     with(s.graphics) beginFill(col), drawCircle(0,0,5);
  136.     if (!noDrag){
  137.         s.buttonMode = true;
  138.        s.addEventListener(MouseEvent.MOUSE_DOWN, onDrag);
  139.     }
  140.     return s;
  141. }
  142. function onDrag(evt:MouseEvent):void {
  143.     evt.currentTarget.startDrag()
  144. }
  145.  
  146. stage.addEventListener(MouseEvent.MOUSE_UP, onUp);
  147. function onUp(evt:MouseEvent):void{
  148.     stopDrag();
  149. }

This is not a snippet, but it uses some functions that could be considered snippets on their own. Take a look at the swf here:

Bezier Intersection Demo

This demo show a brute force method for getting the coordinates of all intersections between two given quadtratic bezier curves. The approach is pretty simple, each bezier is actually made up of a series of line segments. The resolution variable determines how many line segments make up one bezier curve. By default I use a resolution of 0.03 (~34 lines)... the higher the resolution decimal value, the fewer the number of line segments. I then use a slight variation on yesterdays line segment intersection function to test all existing line segments for intersections.

This is a brute for approach with lots of room for improvement. But in the scenario that you only need to check a few bezier curves for intersection this approach works quite nicely. I don't recommend this approach if your trying to create a complex vector drawing tool with boolean vector operations etc...

It's easy to get an idea of the different approaches to this problem with a little googling. One example I found is from Graphics Gems:

http://tog.acm.org/GraphicsGems/gemsiv/curve_isect/

it's been awhile, but I believe this website also contains information related to this topic:

http://algorithmist.wordpress.com/

Posted in Math, bezier | Also tagged | Leave a comment