int res = 2;
  int penSize = 30;
  int lwidth;
  int lheight;
  int pnum = 30000;
  vsquare[][] v;
  vbuffer[][] vbuf;
  particle[] p;
  int pcount = 0;
  int mouseXvel = 0;
  int mouseYvel = 0;
  
  int randomGust = 0;
  int randomGustMax;
  float randomGustX;
  float randomGustY;
  float randomGustSize;
  float randomGustXvel;
  float randomGustYvel;
  
  void setup() 
  {
    size(200, 200);
    lwidth = width/res;
    lheight = height/res;
    v = new vsquare[lwidth+1][lheight+1];
    vbuf = new vbuffer[lwidth+1][lheight+1];
    p = new particle[pnum];
    noStroke();
    for(int i = 0; i < pnum; i++) {
      p[i] = new particle(random(width/2-20,width/2+20),random(height-20,height));
    }
    for(int i = 0; i <= lwidth; i++) {
      for(int u = 0; u <= lheight; u++) {
        v[i][u] = new vsquare(i*res,u*res);
        vbuf[i][u] = new vbuffer(i*res,u*res);
      }
    }
  }
  
  void draw() 
  {
    background(#cccccc);
    
    int axvel = mouseX-pmouseX;
    int ayvel = mouseY-pmouseY;
  
    mouseXvel = (axvel != mouseXvel) ? axvel : 0;
    mouseYvel = (ayvel != mouseYvel) ? ayvel : 0;
  
    if(randomGust <= 0) {
      if(random(0,10)<1) {
        randomGustMax = (int)random(5,12);
        randomGust = randomGustMax;
        randomGustX = random(0,width);
        randomGustY = random(0,height-10);
        randomGustSize = random(0,50);
        if(randomGustX > width/2) {
          randomGustXvel = random(-8,0);
        } else { 
          randomGustXvel = random(0,8);
        }
        randomGustYvel = random(-2,1);
      }
      randomGust--;
    }
  
    for(int i = 0; i < lwidth; i++) {
      for(int u = 0; u < lheight; u++) {
        vbuf[i][u].updatebuf(i,u);
        v[i][u].col = 0;
      }
    }
    for(int i = 0; i < pnum-1; i++) {
      p[i].updatepos();
    }
    for(int i = 0; i < lwidth; i++) {
      for(int u = 0; u < lheight; u++) {
        v[i][u].addbuffer(i, u);
        v[i][u].updatevels(mouseXvel, mouseYvel);
        v[i][u].display(i, u);
      }
    }
    randomGust = 0;
  }
  
  class particle 
  {
    float x;
    float y;
    float xvel;
    float yvel;
    float temp;
    int pos;
  
    particle(float xIn, float yIn) {
      x = xIn;
      y = yIn;
    }
  
    void reposition() {
      x = width/2+random(-20,20);
      y = random(height-10,height);
  
      xvel = random(-1,1);
      yvel = random(-1,1);
    }
  
    void updatepos() {
      int vi = (int)(x/res);
      int vu = (int)(y/res);
  
      if(vi > 0 && vi < lwidth && vu > 0 && vu < lheight) {
        v[vi][vu].addcolour(2);
  
        float ax = (x\%res)/res;
        float ay = (y\%res)/res;
  
        xvel += (1-ax)*v[vi][vu].xvel*0.05;
        yvel += (1-ay)*v[vi][vu].yvel*0.05;
  
        xvel += ax*v[vi+1][vu].xvel*0.05;
        yvel += ax*v[vi+1][vu].yvel*0.05;
  
        xvel += ay*v[vi][vu+1].xvel*0.05;
        yvel += ay*v[vi][vu+1].yvel*0.05;
  
        v[vi][vu].yvel -= (1-ay)*0.003;
        v[vi+1][vu].yvel -= ax*0.003;
  
        if(v[vi][vu].yvel < 0) v[vi][vu].yvel *= 1.00025;
  
        x += xvel;
        y += yvel;
      } 
      else {
        reposition();
      }
      if(random(0,400) < 1) {
        reposition();
      }
      xvel *= 0.6;
      yvel *= 0.6;
    }
  }
  
  class vbuffer
  {
    int x;
    int y;
    float xvel;
    float yvel;
    float pressurex = 0;
    float pressurey = 0;
    float pressure = 0;
  
    vbuffer(int xIn,int yIn) {
      x = xIn;
      y = yIn;
      pressurex = 0;
      pressurey = 0;
    }
  
    void updatebuf(int i, int u) {
      if(i>0 && i<lwidth && u>0 && u<lheight) {
        pressurex = (v[i-1][u-1].xvel*0.5 + v[i-1][u].xvel + v[i-1][u+1].xvel*0.5 - v[i+1][u-1].xvel*0.5 - v[i+1][u].xvel - v[i+1][u+1].xvel*0.5);
        pressurey = (v[i-1][u-1].yvel*0.5 + v[i][u-1].yvel + v[i+1][u-1].yvel*0.5 - v[i-1][u+1].yvel*0.5 - v[i][u+1].yvel - v[i+1][u+1].yvel*0.5);
        pressure = (pressurex + pressurey)*0.25;
      }
    }
  }
  
  class vsquare {
    int x;
    int y;
    float xvel;
    float yvel;
    float col;
  
    vsquare(int xIn,int yIn) {
      x = xIn;
      y = yIn;
    }
  
    void addbuffer(int i, int u) {
      if(i>0 && i<lwidth && u>0 && u<lheight) {
        xvel += (vbuf[i-1][u-1].pressure*0.5
        +vbuf[i-1][u].pressure
        +vbuf[i-1][u+1].pressure*0.5
        -vbuf[i+1][u-1].pressure*0.5
        -vbuf[i+1][u].pressure
        -vbuf[i+1][u+1].pressure*0.5
        )*0.49;
        yvel += (vbuf[i-1][u-1].pressure*0.5
        +vbuf[i][u-1].pressure
        +vbuf[i+1][u-1].pressure*0.5
        -vbuf[i-1][u+1].pressure*0.5
        -vbuf[i][u+1].pressure
        -vbuf[i+1][u+1].pressure*0.5
        )*0.49;
      }
    }
  
    void updatevels(int mvelX, int mvelY) {
      float adj;
      float opp;
      float dist;
      float mod;
  
      if(mousePressed) {
        adj = x - mouseX;
        opp = y - mouseY;
        dist = sqrt(opp*opp + adj*adj);
        if(dist < penSize) {
          if(dist < 4) dist = penSize;
          mod = penSize/dist;
          xvel += mvelX*mod;
          yvel += mvelY*mod;
        }
      }
      if(randomGust > 0) {
        adj = x - randomGustX;
        opp = y - randomGustY;
        dist = sqrt(opp*opp + adj*adj);
        if(dist < randomGustSize) {
          if(dist < res*2) dist = randomGustSize;
          mod = randomGustSize/dist;
          xvel += (randomGustMax-randomGust)*randomGustXvel*mod;
          yvel += (randomGustMax-randomGust)*randomGustYvel*mod;
        }
      }
      xvel *= 0.99;
      yvel *= 0.98;
    }
  
    void addcolour(int amt) {
      col += amt;
      if(col > 196) col = 196;
    }
  
    void display(int i, int u) {
      float tcol = 0;
      if(i>0 && i<lwidth-1 && u>0 && u<lheight-1) {
  
        tcol = (+ v[i][u+1].col
        + v[i+1][u].col
        + v[i+1][u+1].col*0.5
        )*0.3;
        tcol = (int)(tcol+col*0.5);
      }
  
      fill(255-tcol, 255-tcol, 255-tcol);
      rect(x,y,res,res);
      col = 0;
    }
  }