Use neighbourhoods to optimise the collision detection.
As there are large collidable images, it is vital that they are placed into multiple squares.
i.e. they will need a new Collision strategy object.
Maybe allow the editor to have multiple layers.
Background images go on the background layer automatically.
If we do that we might as well have a foreground layer too, which allows the ships to be hidden
while moving through tunnels.
Note, the effects layer would have to be below the foreground layer.
i.e. background, main, effets, foreground.
Make the first such tunnal objvious, by making the entrance and exit long and thin.
Later, you can test for holes using your bullets.
Explosions and other non-interacting, but moving objects go in their own layer above the others.
The background layer, and the main layer can be rendered using neighbourhoods.
Useful if the world if large, because then many objects won't be considered for rendering.
Ensire that the redrawing checks the alpha channel, if it has one, then it
Game ideas
==========
Gates to end the level.
Water and other liquids - cause lots of drag.
Need to fill up the bucket to get the water/fuel.
Maybe the collision is done using math rather than pixels.
Pixels *could* tell you when it partually and fully submerged - by using a second image below the sutface.
Doors and buttons
Have them swing back on hinges.
Gun emplacements (like thrust)
Random, aimed, seeking. Laser (use a succession of small lines, till one hits).