/*

 2D FLUID SOLVER BASED ON JOS STAM PAPER:
 http://www.dgp.toronto.edu/people/stam/reality/Research/pdf/GDC03.pdf
 
 /////////////////////////////////////////////////////////////////////
  
 CONTROLS:
  - clic left to add forces
  - clic right to increase density
  - press 's' to add a source
  - press 'v' to show/hide velocity field
  - press 'd' to show/hide density field
  - press 'g' to show/hide grid latter
  - press 'p' to show/hide particles (no update)  
  - press 'r' to restore all (except for lagrangian particles)
 
 /////////////////////////////////////////////////////////////////////
 
*/