Xgas, animated simulation of an ideal gas

Xgas is a physical simulation of an ideal gas in a heated box.  Gas molecules
move around the box with velocities dependent on their temperature.  A chamber
consisting of two boxes contains the gas molecules collide with the walls, their
temperature approaches that of the box.

Use mouse button 1 to create molecules one at a time at the cursor position.
Use mouse button 2 to create the maximum number of molecules at the cursor
position.

Usage: xgas [ -options ]

Options:
      -as   Sets the autoStart resource.
      -ts   Sets the timeStepSize resource.
      -d    Sets the delay resource.
      -rb   Sets the randomBounce resource.
      -eq   Sets the equilibrium resource.
      -mm   Sets the maxMolecules resource.
      -fg   Sets the foreground.
      -bg   Sets the background.