// Fluid 
// by Glen Murphy <http://www.bodytag.org> 

int res = 2; 
int penSize = 30; 
int lwidth; 
int lheight; 
int pnum = 30000; 
vsquare[][] v; 
vbuffer[][] vbuf; 
particle[] p = new particle[pnum]; 
int pcount = 0; 
int mouseXvel = 0; 
int mouseYvel = 0; 
 
void setup() 
{ 
  size(200,200); 
  noStroke(); 
  framerate(30); 
  lwidth = width/res; 
  lheight = height/res; 
  v = new vsquare[lwidth+1][lheight+1]; 
  vbuf = new vbuffer[lwidth+1][lheight+1]; 
  for(int i = 0; i < pnum; i++) { 
    p[i] = new particle(random(res,width-res),random(res,height-res)); 
    } 
  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(#666666); 
  
  int axvel = mouseX-pmouseX; 
  int ayvel = mouseY-pmouseY; 
 
  mouseXvel = (axvel != mouseXvel) ? axvel : 0; 
  mouseYvel = (ayvel != mouseYvel) ? ayvel : 0; 
 
  for(int i = 0; i < lwidth; i++) { 
    for(int u = 0; u < lheight; u++) { 
      vbuf[i][u].updatebuf(i,u); 
      v[i][u].col = 32; 
    } 
  } 
  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); 
    } 
  } 
} 
 
class particle { 
  float x; 
  float y; 
  float xvel; 
  float yvel; 
  int pos; 
  particle(float xIn, float yIn) { 
    x = xIn; 
    y = yIn; 
  } 
 
  void updatepos() { 
    float col1; 
    if(x > 0 && x < width && y > 0 && y < height) { 
      int vi = (int)(x/res); 
      int vu = (int)(y/res); 
      vsquare o = v[vi][vu];    
      
      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; 
 
      o.col += 4; 
      
      x += xvel; 
      y += yvel; 
    } 
    else { 
      x = random(0,width); 
      y = random(0,height); 
      xvel = 0; 
      yvel = 0; 
    } 
 
    xvel *= 0.5; 
    yvel *= 0.5; 
  } 
} 
 
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 
              )*0.25; 
      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 
              )*0.25; 
      } 
    } 
 
  void updatevels(int mvelX, int mvelY) { 
    if(mousePressed) { 
      float adj = x - mouseX; 
      float opp = y - mouseY; 
      float dist = sqrt(opp*opp + adj*adj); 
      if(dist < penSize) { 
        if(dist < 4) dist = penSize; 
        float mod = penSize/dist; 
        xvel += mvelX*mod; 
        yvel += mvelY*mod; 
        } 
      } 
 
    xvel *= 0.99; 
    yvel *= 0.99; 
  } 
  
  void display(int i, int u) { 
    float tcol = 0; 
    if(col > 255) col = 255; 
    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 
              )*0.4; 
      tcol = (int)(tcol+col*0.5); 
      } 
    else { 
      tcol = (int)col; 
      } 
    fill(tcol, tcol, tcol); 
    rect(x,y,res,res); 
  } 
}