A simple prototype of a falling-sand game, with only 2 types of particles:
moving sand and immobile obstacle.
Space to pause/unpause the game.
R to toggle rain of sand.
D to print debug information to standard output
Left mouse button to draw obstacles.
Right mouse button to delete obstacles and sand.
Change WINDOW_HEIGHT and WINDOW_WIDTH const to adjust the size of the game screen.
Change RAIN_SPARSENESS const to change the density of the falling sand.
This program might require installation of freetype and SDL2 libraries to work.
Compiles with: rustc 1.18.0 (03fc9d622 2017-06-06)
