# Monthly Archives: March 2010

## Clock Quiz

Here is a quick sunday quiz. Create some kind of clock with as little code as possible. Even just a textfield and the date object would cut it, but preferably try to do something a little more interesting. Post your results in the comments. I’ll post my version on monday EOD.

[EDIT: my clock can be found here which I'll count as tomorrows post]

The last clock post I did was about the 24 hour clock have a look at that here.

Posted in Quiz | Tagged , , , | 19 Comments

Actionscript:
1. initOperators();
2.
3. trace(zipWith("-", [1,2,3], [1,2,3]));
4. trace(zipWith("+", [1,2,3], [1,2,3]));
5. trace(zipWith("*", [1,2,3], [1,2,3]));
6. trace(zipWith("+", [1,1,1,3], [4,5,6,7]));
7. trace(zipWith("<<", [2, 4], [1,1]));
8. /*
9. outputs:
10.
11. 0,0,0
12. 2,4,6
13. 1,4,9
14. 5,6,7,10
15. 4,8
16. */
17.
18. function zipWith(op:String, a:Array, b:Array):Array{
19.     var aLeng:int = a.length;
20.     var bLeng:int = b.length;
21.     var leng:Number = (aLeng <bLeng) ? aLeng : bLeng;
22.     var zipped:Array = [];
23.
24.     if (!this[op])return [];
25.
26.     for (var i:int = 0; i<leng; i++){
27.         zipped[i]=this[op](a[i], b[i]);
28.     }
29.     return zipped;
30. }
31.
32. function initOperators():void{
33.     this["+"]=function(a:Number, b:Number):Number{ return a + b };
34.     this["-"]=function(a:Number, b:Number):Number{ return a - b };
35.     this["/"]=function(a:Number, b:Number):Number{ return a / b };
36.     this["*"]=function(a:Number, b:Number):Number{ return a * b };
37.     this["%"]=function(a:Number, b:Number):Number{ return a % b };
38.
39.     this["&"]=function(a:Number, b:Number):Number{ return a & b };
40.     this["<<"]=function(a:Number, b:Number):Number{ return a <<b };
41.     this["|"]=function(a:Number, b:Number):Number{ return a | b };
42.     this[">>"]=function(a:Number, b:Number):Number{ return a>> b };
43.     this[">>>"]=function(a:Number, b:Number):Number{ return a>>> b };
44.     this["^"]=function(a:Number, b:Number):Number{ return a ^ b };
45. }

This snippet is basically like the haskell zipWith() function. It can combines two arrays into one array given a single function. In this case I defined a bunch of operator functions, but it would work with any kind of function that takes two arguments and returns a value. You could extend this to work with strings and do other strange things I guess.

If you have yet to go play with haskell ... go do it now.

Posted in Number, Operators, arrays, binary, functions, misc, return values | Tagged , , , | 2 Comments

## Frame Differencing

Actionscript:
1. [SWF(width = 800, height= 600)]
2. var sw:Number = 800;
3. var sh:Number = 600;
4. var pixelNum:int = sw * sh;
5. var blurAmount:Number = 10;
6. var pnt:Point = new Point(0,0);
7. var rect:Rectangle = new Rectangle(0,0,sw,sh);
8.
9. var canvas:BitmapData = new BitmapData(sw, sh, false, 0x000000);
10. var buffer:BitmapData = new BitmapData(sw, sh, false, 0x000000);
11. var feed  :BitmapData = new BitmapData(sw, sh, false, 0x000000);
12. var prev  :BitmapData = new BitmapData(sw, sh, false, 0x000000);
13.
14. var frame:Bitmap = new Bitmap(canvas, "auto", true);
16.
17. var cam:Camera =  Camera.getCamera();
18. cam.setMode(sw,sh,12);
19. var video:Video = new Video(sw, sh);
20. video.attachCamera(cam);
21.
23.
24. function onActivityStart(evt:ActivityEvent):void {
26.     cam.removeEventListener(ActivityEvent.ACTIVITY, onActivityStart);
27. }
28.
29. function onRun(evt:Event):void{
30.     buffer.draw(video);
31.     feed.copyPixels(buffer, rect, pnt);
32.     buffer.draw(prev, null, null, BlendMode.DIFFERENCE);
33.     prev.draw(video);
34.     canvas.copyPixels(buffer, rect, pnt);
35. }

This snippet shows a simple method to do frame differencing with a web cam. This is useful for detecting which areas of the screen have change from frame to frame. This post assumes you pretty much know what frame differencing is.

You can view an swf file here: This is one of those things I do a good deal but never wrapped up into a library... it's easy (for me at least) to forget exactly how to set it up from scratch.

I added an extra buffer because it's pretty common that you'll want to other things aside from just frame differencing alone, so it's nice to have it all wrapped up in a buffer BitmapData that you can use elsewhere. If speed is a real concern, you can do away with the buffer and just use the canvas instead - depending on what kind of analysis your doing on the frame differenced image it may be trickier without the buffer.

| Tagged , , | 5 Comments

## Functions as Object Review

Something I do a fair bit on this website is use functions as objects. Here is a simple example post on wonderfl. Timeline code and a brief description are available below.

Here is a still of what it generates and below you'll find the timeline as code: Actionscript:
1. [SWF(width = 500, height=500)]
2.
3. var canvas:BitmapData = new BitmapData(800,800,false, 0x000000);
5. scaleX = scaleY = 500 / 800
6.
7.
8. var walkerNum:int = 50;
9. var walkers:Vector.<Function> = new Vector.<Function>(walkerNum, true);
10.
11. makeWalkers();
12. runWalkers();
13.
14. function makeWalkers():void{
15.     for (var i:int = 0; i<walkerNum; i++){
16.         walkers[i] = makeWalker();
17.     }
18. }
19. function runWalkers():void{
21. }
22. function onRun(evt:Event):void{
23.     for (var i:int = 0; i<walkerNum; i++){
24.         walkers[i]();
25.     }
26. }
27.
28. function makeWalker(xp:Number=400, yp:Number=400):Function{
29.     var x:Number = xp, y:Number = yp;
30.     var rad:Number = Math.random() * 4;
31.     var theta:Number = Math.random() * Math.PI * 2;
32.     var speed:Number = 0.01 * Math.random() * 2
33.     if (int(Math.random() * 2) == 1){
34.         speed *= -1;
35.     }
36.     return function():void{
37.         x += rad * Math.cos(theta);
38.         y += rad * Math.sin(theta);
39.         theta += speed
40.         if (int(Math.random() * 100) == 1){
41.             theta = Math.random() * Math.PI * 2;
42.         }
43.         if (x> 800 || x <0 || y> 800 || y <0){
44.             x = xp, y = yp;
45.         }
46.         canvas.setPixel(x, y, 0xFFFFFF);
47.     }
48. }

The basic trick is to have a function return a function. The original function initializes typed local variables and the returned function has access to these values. This is one of many ways to do OOP style coding using functions alone. This is really only for fun and for speed coding reasons - it's worth noting that this method is is significantly slower than using actual classes. I still have lots of fun with it despite the downsides.

Posted in BitmapData, functions | Tagged , , | 7 Comments

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