Sprites / grid system

[bpierre]

See 5d0d391

(I just take notes, don’t fix this now)

The doors depth need to be 16 or 18, not 17 (because coordinates are centered, and 16 is better because the grid is based on 32x32 squares).

Their width need to be a divisor of 800 (if we exclude the walls outside by modifying the canvas dimensions), but maybe we can add an exception for the doors, to allow the wall junction (on the sprites, the door itself fits in 32px, so we have the 25 cells: 25 × 32px = 800px).