Category Archives: graphics algorithms

Frame Differencing

By Zevan | March 11, 2010
CLICK HERE TO COPY
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);
  15. addChild(frame);
  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.  
  22. cam.addEventListener(ActivityEvent.ACTIVITY, onActivityStart);
  23.  
  24. function onActivityStart(evt:ActivityEvent):void {
  25.     addEventListener(Event.ENTER_FRAME, onRun);
  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.

Also posted in BitmapData, Video, pixel manipulation | Tagged , , | 5 Comments

~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, display list, matrix, misc, pixel manipulation, return values | Tagged , , | 2 Comments

Utils3D.projectVectors() Lathe

By Zevan | July 6, 2009
CLICK HERE TO COPY
Actionscript:
  1. [SWF(width = 500, height = 500, backgroundColor = 0x000000)]
  2. var halfWidth:Number = stage.stageWidth / 2;
  3. var halfHeight:Number = stage.stageHeight / 2;
  4. var loc:Vector.<Number>;
  5.  
  6. graphics.lineStyle(0, 0xFF0000);
  7. graphics.moveTo(halfWidth, 0);
  8. graphics.lineTo(halfWidth, stage.stageHeight);
  9. graphics.moveTo(0, halfHeight);
  10. graphics.lineTo(stage.stageWidth, halfHeight);
  11.  
  12. var line:Shape = Shape(addChild(new Shape()));
  13. line.x = halfWidth;
  14.  
  15. var idle:Function = function(){};
  16. var currentMode:Function = idle;
  17. stage.addEventListener(MouseEvent.MOUSE_DOWN, onDown);
  18. stage.addEventListener(MouseEvent.MOUSE_UP, onUp);
  19. addEventListener(Event.ENTER_FRAME, onLoop);
  20. function onDown(evt:MouseEvent):void{
  21.     if (contains(frame)){
  22.         removeChild(frame);
  23.         currentMode = idle;
  24.         line.graphics.clear();
  25.         return;
  26.     }
  27.     loc = new Vector.<Number>();
  28.     line.graphics.lineStyle(0,0xFFFFFF);
  29.     line.x = halfWidth
  30.     line.y = halfHeight;
  31.     line.graphics.moveTo(line.mouseX, line.mouseY);
  32.     currentMode = captureLocs;
  33.     canvas.fillRect(canvas.rect, 0x000000);
  34. }
  35. function onUp(evt:MouseEvent):void{
  36.     if (currentMode == idle) return;
  37.     setupLathe();
  38.     currentMode = showLathe;
  39. }
  40.  
  41. function onLoop(evt:Event):void{
  42.     currentMode();
  43. }
  44. function captureLocs():void{
  45.     loc.push(line.mouseX);
  46.     loc.push(line.mouseY);
  47.     loc.push(0);
  48.     line.graphics.lineTo(line.mouseX, line.mouseY);
  49. }
  50. /**
  51.  -- Lathe Stuff:
  52. */
  53. var canvas:BitmapData = new BitmapData(stage.stageWidth, stage.stageHeight,false, 0x000000);
  54. var frame:Bitmap = new Bitmap(canvas);
  55. var dx:Number=0;
  56. var dy:Number=0;
  57.  var matrix:Matrix3D = new Matrix3D();
  58. var pVerts:Vector.<Number>;
  59. var uvts:Vector.<Number>;
  60. function setupLathe():void{
  61.     addChild(frame);
  62.     pVerts =  new Vector.<Number>();
  63.     uvts = new Vector.<Number>();
  64.     var nVerts:Vector.<Number> = new Vector.<Number>();
  65.     var tVerts:Vector.<Number> = new Vector.<Number>();
  66.     matrix.identity();
  67.     var step:Number = 2;
  68.     for (var i:int = 0; i <360; i+=step){
  69.         matrix.appendRotation(step,Vector3D.Y_AXIS);
  70.         matrix.transformVectors(loc, tVerts);
  71.         nVerts = nVerts.concat(tVerts);
  72.     }
  73.     loc = nVerts.concat();
  74. }
  75. function showLathe():void{
  76.     dx += (mouseX - dx)/4;
  77.     dy += (mouseY - dy)/4;
  78.     matrix.identity();
  79.     matrix.appendRotation(dy,Vector3D.X_AXIS);
  80.     matrix.appendRotation(dx,Vector3D.Y_AXIS);
  81.     matrix.appendTranslation(halfWidth, halfHeight, 0);
  82.     Utils3D.projectVectors(matrix, loc, pVerts, uvts);
  83.     canvas.lock();
  84.     canvas.fillRect(canvas.rect, 0x000000);
  85.     var leng:int = pVerts.length;
  86.     for (var i:int = 0; i<leng; i+=2){
  87.         canvas.setPixel( pVerts[i], pVerts[i + 1], 0xFFFFFF);
  88.     }
  89.     canvas.unlock();
  90. }

This snippet allows you to create 3D lathe shapes by drawing a 2D line. This is done using Utils3D.projectVectors() and Matrix.transformVectors().

Have a look at the swf here...

Also posted in 3D, BitmapData, Math, Vector, matrix, setPixel | Tagged , , | 3 Comments

Bresenham’s Circle and setVector()

By Zevan | June 30, 2009
CLICK HERE TO COPY
Actionscript:
  1. var canvasSize:int = 400;
  2. var canvas:BitmapData = new BitmapData(canvasSize, canvasSize, false, 0xFFFFFF);
  3. addChild(new Bitmap(canvas));
  4. var size:int = canvas.width * canvas.height;
  5. var pixels:Vector.<uint> = canvas.getVector(canvas.rect);
  6.  
  7. addEventListener(Event.ENTER_FRAME, onLoop);
  8. function onLoop(evt:Event):void {
  9.      for (var i:int = 0; i<500; i++){
  10.       fillCircle(int(Math.random() * canvasSize),
  11.                       int(Math.random() * canvasSize),
  12.                       int(Math.random() * 5 + 3),
  13.                       uint(Math.random() * 0xFFFF));
  14.      }
  15.      canvas.lock();
  16.      canvas.setVector(canvas.rect, pixels);
  17.      canvas.unlock();
  18. }
  19.  
  20. function fillCircle(xp:int,yp:int, radius:int, col:uint = 0x000000):void {
  21.     var xoff:int =0;
  22.     var yoff:int = radius;
  23.     var balance:int = -radius;
  24.     while (xoff <= yoff) {
  25.          var p0:int = xp - xoff;
  26.          var p1:int = xp - yoff;
  27.          var w0:int = xoff + xoff;
  28.          var w1:int = yoff + yoff;
  29.          hLine(p0, yp + yoff, w0, col);
  30.          hLine(p0, yp - yoff, w0, col);
  31.          hLine(p1, yp + xoff, w1, col);
  32.          hLine(p1, yp - xoff, w1, col);
  33.         if ((balance += xoff++ + xoff)>= 0) {
  34.             balance-=--yoff+yoff;
  35.         }
  36.     }
  37. }
  38. function hLine(xp:int, yp:int, w:int, col:uint):void {
  39.     var index:int = xp + yp * canvasSize;
  40.     for (var i:int = 0; i <w; i++){
  41.         index++;
  42.         if (index> -1 && index <size){
  43.           pixels[index] = col;
  44.         }
  45.     }
  46. }

In the past I've posted examples of Bresenham's Circle (here and here). Both of those examples make use of setPixel(). Today's snippet demos a version of Bresenham's Circle that works with setVector().

Also posted in BitmapData, pixel manipulation, setPixel | Tagged , , , | Leave a comment