Category Archives: display list

~20,000 Rollovers

By Zevan | January 3, 2010
CLICK HERE TO COPY
Actionscript:
  1. [SWF(width = 500, height = 500, frameRate = 30)]
  2.  
  3. var canvas:BitmapData = new BitmapData(stage.stageWidth,stage.stageHeight,false, 0xFFFFFF);
  4.  
  5. var indexCanvas:BitmapData = new BitmapData(stage.stage.stageWidth, stage.stageHeight, false,
  6.                                             0xFFFFFF);
  7. addChild(new Bitmap(canvas));
  8.  
  9. var s:Shape = new Shape();
  10.  
  11. var lineData:Array = [];
  12. var dataIndex:int = 0;
  13.  
  14. trace(0xFFFFFF - 1)
  15. var totalLines:int = 20000;
  16. var iterations:int = 9;
  17. var linesPerIter:int = totalLines / iterations;
  18.  
  19. var xp:int = stage.stageWidth / 2;
  20. var yp:int = stage.stageHeight / 2;
  21.  
  22. var stepAmt:Number = 60;
  23. var halfStepAmt:Number = stepAmt / 2;
  24.  
  25. addEventListener(Event.ENTER_FRAME, onDraw);
  26. function onDraw(evt:Event):void {
  27.      if (lineData.length <totalLines){
  28.         generateData(linesPerIter);
  29.      }else{
  30.         stage.quality = "high";
  31.         addChild(s);
  32.         s.x = 0;
  33.         s.y = 0;
  34.          
  35.         removeEventListener(Event.ENTER_FRAME, onDraw);
  36.         addEventListener(Event.ENTER_FRAME, onRun);
  37.      }
  38. }
  39.  
  40. function onRun(evt:Event):void {
  41.    var currentIndex:int = indexCanvas.getPixel(mouseX, mouseY);
  42.    var currentLine:Array = lineData[currentIndex];
  43.    
  44.    s.graphics.clear();
  45.    if (currentIndex != 0xFFFFFF){
  46.           s.graphics.lineStyle(3, 0xFF0000);
  47.           s.graphics.moveTo(currentLine[0], currentLine[1]);
  48.           s.graphics.lineTo(currentLine[2], currentLine[3]);  
  49.    }
  50. }
  51.  
  52. function generateData(num:int):void{
  53.     var rxA:int, rxB:int, ryA:int, ryB:int;
  54.     var g:Graphics = s.graphics;
  55.     for (var i:int = 0; i<num; i++){
  56.         rxA = xp;
  57.         ryA = yp;
  58.        
  59.         xp += Math.round(Math.random() * stepAmt) - halfStepAmt;
  60.         yp += Math.round(Math.random() * stepAmt) - halfStepAmt;
  61.        
  62.         if (xp> stage.stageWidth){
  63.             xp = stage.stageWidth - halfStepAmt;
  64.         }else
  65.         if (xp <0){
  66.             xp = halfStepAmt;
  67.         }
  68.         if (yp> stage.stageHeight){
  69.             yp = stage.stageHeight - halfStepAmt;
  70.         }else
  71.         if (yp <0){
  72.             yp = halfStepAmt;
  73.         }
  74.        
  75.         rxB = xp;
  76.         ryB = yp;
  77.          
  78.         lineData[dataIndex] = [rxA, ryA, rxB, ryB];            
  79.         s.x = rxA;
  80.         s.y = ryA;
  81.         var endX:Number = rxB - rxA;
  82.         var endY:Number = ryB - ryA;
  83.         var m:Matrix = s.transform.matrix;
  84.         g.clear();
  85.         g.lineStyle(1, 0x000000, 0.3);
  86.  
  87.         g.lineTo(endX, endY);
  88.         stage.quality = "high";
  89.         canvas.draw(s, m);
  90.        
  91.         g.clear();
  92.         g.lineStyle(3, dataIndex);
  93.        
  94.         g.lineTo(endX, endY);
  95.         stage.quality = "low";
  96.         indexCanvas.draw(s, m);
  97.        
  98.         dataIndex++
  99.     }
  100. }

I'm working on a data visualization that contains a long path made up of approximately one million points. There is some information associated with every two sets of coordinates that needs to be displayed when the user rolls their mouse over any part of the line.

I took a little time to think about the best way to do this and came up with a few techniques. The first one I tried seems to work nicely - this snippet is the proof of concept for that first technique. I tested this snippet with 1,000,000 xy coordinates and it works nicely. It takes a little while to draw though, so for the purposes of this demo I've just included 20,000 coordinates.

Have a look at the swf over at wonderfl.net

The way this works is by drawing lines to two different BitmapData instances. I draw anti-aliased slightly transparent lines to a BitmapData instance called "canvas" (this is added to the display list) - I then draw aliased lines to a BitmapData called "indexCanvas" (this is never added to the display list) - each aliased line uses an incremental value for its color - this incremental value is also the index for a two dimensional array containing the coordinate information for the aliased line. I use getPixel() on the "indexCanvas" and use the return value as the index for the 2D array. The data from the 2D array is used to draw a red line with the graphics class. This technique enables you to have many many rollovers and all you ever have to do is call getPixel() and use the returned color value to look up info about what you're mouse is touching.

There are a few cool ways this could be repurposed and this is really only one solution to the problem of having many many things that you need to be able to rollover... there are others that don't use BitmapData at all... I may write those up in the next couple of days.

Also posted in BitmapData, Data Structures, UI, arrays, graphics algorithms, matrix, misc, pixel manipulation, return values | Tagged , , | 2 Comments

Bring Display Object to Top

By Zevan | December 21, 2008
CLICK HERE TO COPY
Actionscript:
  1. mc.addEventListener(MouseEvent.ROLL_OVER, onRollOver);
  2. function onRollOver(evt:MouseEvent):void {
  3.   addChild(MovieClip(evt.currentTarget));
  4. }

This one is very simple, but it's important to note that using addChild() on something that is already on the display list simply brings it to the top. Back in AS2 we used to do:

CLICK HERE TO COPY
Actionscript:
  1. mc.swapDepths(1000);

Also posted in DisplayObject | Tagged , | 3 Comments

Reset Registration Point

By Zevan | November 19, 2008
CLICK HERE TO COPY
Actionscript:
  1. // display object target, value - "center" or "upperLeft"
  2. function setRegistration(dsp:DisplayObjectContainer, v:String):void {
  3.     var i:int;
  4.     var child:DisplayObject;
  5.     var b:Rectangle=getBounds(dsp);
  6.     for (i = 0; i <dsp.numChildren; i++) {
  7.         child=dsp.getChildAt(i);
  8.         child.x+=b.x*-1;
  9.         child.y+=b.y*-1;
  10.     }
  11.     if (v=="center") {
  12.         dsp.x+=dsp.width/2;
  13.         dsp.y+=dsp.height/2;
  14.         for (i = 0; i <dsp.numChildren; i++) {
  15.             child=dsp.getChildAt(i);
  16.             child.x-=dsp.width/2;
  17.             child.y-=dsp.height/2;
  18.         }
  19.     } else if (v == "upperLeft") {
  20.         if (dsp.parent) {
  21.             b=getBounds(dsp.parent);
  22.             dsp.x=b.left;
  23.             dsp.y=b.top;
  24.         }
  25.     }
  26. }
  27.  
  28. // example:
  29. // (make a MovieClip and fill it with, text, shapes etc...)
  30.  
  31. setRegistration(clip, "center");
  32. // registration(clip, "upperLeft");
  33.  
  34. addEventListener(Event.ENTER_FRAME, onLoop);
  35. function onLoop(evt:Event):void {
  36.     clip.rotation+=1;
  37. }

Teaching beginner flash... I've noticed people always get confused about the registration point. They think they should be able to move it with the IDE or ActionScript. I always say "You can't change the registration point, you can only change the position of graphical elements in relationship to it." Anyway, as a sort of joke one day after class I wrote the above function... it changes the registration of any DisplayObjectContainer to either "center" or "upperLeft".

To test this code out, fill a MovieClip with a bunch of different things (text, graphics, scribbles)... give it a strange registration point and then run the above code on it. You'll be able to tell that the registration has changed by the way the clip rotates. Although I haven't been able to break this function, I think it's possible that it doesn't work under all circumstances.

Using reparenting is a more elegant solution to this issue. Maybe I'll post that in the next couple days.

Also posted in DisplayObject | Tagged , , | 2 Comments