Fade in / out Motion Trails

soundsound

Hi,

i found a code i'm working on and it basically draws a trail of one's movement (cam). I've been trying to change something but i wasn't able to do it on my own. What i want is the dots to fade in but also to fade out after a certain amount of time. (Let's say 2minutes)

I'd be grateful if anyone could help me with that. Here's the original code: (Works in Processing 1.5.1)

    import processing.video.*;
    Capture video;

    int numPixels;
    int[] previousFrame;
    int[][] diffPoints;
    int diffAmount = 0;

    int particleMin = 2;
    int particleAlpha = 100;

    void setup() 
    {
      size(640, 480);
      background (255);
      noStroke();
      frameRate(30);
      fill(100);
      smooth();
      video = new Capture(this, width, height, 30);
      numPixels = width * height;
      previousFrame = new int[numPixels];
      diffPoints = new int[height][width];
    }

    void captureEvent(Capture video) {
      video.read();
    }

    void draw() 
    {
      diffAmount = 0;
      for (int i = 0; i < numPixels; i++) 
      {
        diffPoints[abs(i / width)][i % width] = 0;
        color currColor = video.pixels[i];
        color prevColor = previousFrame[i];
        // Extract the red, green, and blue components from current pixel
        int currR = (currColor >> 16) & 0xFF; // Like red(), but faster
        int currG = (currColor >> 8) & 0xFF;
        int currB = currColor & 0xFF;
        // Extract red, green, and blue components from previous pixel
        int prevR = (prevColor >> 16) & 0xFF;
        int prevG = (prevColor >> 8) & 0xFF;
        int prevB = prevColor & 0xFF;
        // Compute the difference of the red, green, and blue values
        int diffR = abs(currR - prevR);
        int diffG = abs(currG - prevG);
        int diffB = abs(currB - prevB);
        // Render the difference image to the screen
        color diff = color(diffR, diffG, diffB);
        int isPointDiff = 0;
        if (diff > -15000000)      //-16777216
        {
          isPointDiff = 1;
          ++diffAmount;
        }
        diffPoints[abs(i / width)][i % width] = isPointDiff;
      }
      checkForNewPoint(diffAmount);

      arraycopy(video.pixels, previousFrame);  
    }

    void checkForNewPoint(int diffAmount)
    {  
      if(diffAmount > 100000) 
      {
        return;
      }
      float milliseconds = millis();
      if (milliseconds < 1000) return;
      if (diffAmount < 40) return;
      int blocks = 0;
      for (int i = 0; i < height; i++) 
      {
        for (int j = 0; j < width; j++)
        {      
          if(i > 1 && j > 1 && diffPoints[i][j] == 1)
          {
            if(diffPoints[i - 1][j] == 1 && diffPoints[i - 2][j] == 1 
                || diffPoints[i][j - 1] == 1 && diffPoints[i][j - 2] == 1)
            {
              ++blocks;
              int randNum = 10;
              int randX = int((randNum / 2) - random(randNum));
              int randY = int((randNum / 2) - random(randNum)); 
              color c = previousFrame[(i * width) + j];
              fill(c, particleAlpha);
              int particleSize = diffAmount / 700;

              if(random(particleSize) > (particleSize - (.9999999 / particleSize))) 
              {
                ellipse(j, i, particleMin + particleSize, particleMin + particleSize);
              }
            }
          }
        }
      }  
    }

    void mousePressed() {
      fill(255);
      rect(0, 0, width, height);
    }