Monthly Archives: March 2009

Low Precision Sine and Cosine

By Zevan | March 21, 2009

Actionscript:

var t:Number=0, cos:Number, sin:Number;
 
var canvas:BitmapData = new BitmapData(400,400,false, 0x000000);
addChild(new Bitmap(canvas));
 
var shape:Shape = new Shape();
with(shape.graphics) beginFill(0x568338, .2), drawCircle(0,0,10);
 
addEventListener(Event.ENTER_FRAME, onLoop);
function onLoop(evt:Event):void {
    
         t += .1;
        // -- low precision sine/cosine
        //always wrap input angle to -PI..PI
        if (t <-3.14159265){
            t += 6.28318531;
        }else{
        if (t>  3.14159265)
            t -= 6.28318531;
        }
        
        //compute sine
        if (t <0){
            sin = 1.27323954 * t + .405284735 * t * t;
        }else{
            sin = 1.27323954 * t - 0.405284735 * t * t;
        }
        
        //compute cosine: sin(t + PI/2) = cos(t)
        t += 1.57079632;
        if (t>  3.14159265){
            t -= 6.28318531;
        }
        
        if (t <0){
            cos = 1.27323954 * t + 0.405284735 * t * t
        }else{
            cos = 1.27323954 * t - 0.405284735 * t * t;
        }
        t -= 1.57079632;
        
        // move the shape
        shape.x = 200 + 100 * cos;
        shape.y = 200 + 100 * sin;
        
        // draw to the canvas
        canvas.draw(shape, shape.transform.matrix);
}

This snippet draws a circle using low precision sine and cosine... you'll notice that its not a perfect looking circle:

Back in January I saw this blog post by Michael Baczynski over at http://lab.polygonal.de/. The blog post describes a technique for fast sine and cosine approximation - (I highly recommend giving it a read - very fun stuff).

It's worth noting that there is a higher precision sine and cosine that will likely draw a better looking circle but will be about half as fast. According to the original post ... the low precision technique is approximately 14x faster than using Math.cos()/Math.sin().

There some other really great posts over at polygonal go check them out.

Posted in Math, motion | Tagged actionscrpt, flash | 2 Comments

Unique Array Comparison

By Zevan | March 20, 2009

CLICK HERE TO COPY

Actionscript:

function uniqueCompare(arr:Array, compare:Function):void {
    var leng:int = arr.length;
    for (var i:int = 0; i<leng; i++){
        for (var j:int = i + 1; j<leng; j++){
            compare(arr[i], arr[j]);
        }
    }
}
 
var numbers:Array = [1, 2, 3, 4, 5];
 
uniqueCompare(numbers, compareCallback);
 
function compareCallback(a:*, b:*):void {
    trace("compare " + a + " to " + b);
}
 
/*
outputs:
compare 1 to 2
compare 1 to 3
compare 1 to 4
compare 1 to 5
compare 2 to 3
compare 2 to 4
compare 2 to 5
compare 3 to 4
compare 3 to 5
compare 4 to 5
*/

This snippet shows a function called uniqueCompare() that compares all elements in an array to all other elements in an array without repeating a comparison.

Posted in arrays, misc | Tagged actionscript, flash | Leave a comment

Object.constructor()

By Zevan | March 19, 2009

CLICK HERE TO COPY

Actionscript:

var Box:Function = {
    constructor : function(color:uint, w:Number, h:Number):void {
        this.color = color;
        this.s = new Shape();
        with(this.s.graphics) beginFill(this.color), drawRect(0,0,w,h);
        addChild(this.s);
        
        this.setLoc = function(x:Number, y:Number):void{
            this.s.x = x;
            this.s.y = y;
       }
    }
}.constructor;
 
var box0:Object = new Box(0xFF0000, 100, 100);
 
box0.setLoc(100, 10);
 
var box1:Object = new Box(0x000000, 50, 50);
 
box1.setLoc(210, 10);

This snippet makes use of Object.constructor() to allow creation of Object instances using the new keyword. This is for fun only, I don't recommend this over actual Classes.

Posted in OOP, dynamic, functions, misc | Tagged actionscript, flash | Leave a comment

Circle of Particles #2

By Zevan | March 18, 2009

CLICK HERE TO COPY

Actionscript:

[SWF(width = 400, height = 400)];
var canvas:BitmapData = new BitmapData(400,400, false, 0x000000);
var eraser:BitmapData = new BitmapData(400,400, true, 0x11000000);
addChild(new Bitmap(canvas));
 
var particles:Array = new Array();
for (var i:int = 0; i <500; i++){
    particles.push(makeParticle());
}
 
addEventListener(Event.ENTER_FRAME, onLoop);
function onLoop(evt:Event):void {
    canvas.copyPixels(eraser, eraser.rect, new Point(0,0), null, null, true);
    for (var i:int = 0; i <particles.length; i++){
        particles[i]();
    }
}
 
function makeParticle():Function {
    var dx:Number, dy:Number;
    var x:Number = 200;
    var y:Number = 200;
    var vx:Number = Math.random() * 4 - 2;
    var vy:Number = Math.random() * 4 - 2;
    var ang:Number;
    return function():void {
              x += vx;
              y += vy;
              dx = 200 - x;
              dy=  200 - y;
               if (Math.sqrt((dx * dx) + (dy * dy))> 130){
                ang = Math.atan2(dy, dx) / Math.PI * 180;
                 vx = Math.cos(ang);
                 vy = Math.sin(ang);
               }
               canvas.setPixel(x, y, 0xFFFFFF);
    }
}