#9: Atop

Initially released December 31, 2012



Source Code:

  • (not available)


You’re a telepathic robot on an island that’s being controlled by an evil robot.  You need to climb to the top of the island to absorb the evil robot sentinel and free the island for robot democracy!

The problem with this plan, of course, is that your robot body can’t actually move.

Luckily, though, you can transfer your consciousness from one robot body to another.  So all you need to do is to expend your energy to create robot bodies in front of you, transfer your consciousness into those bodies, and then re-absorb  the bodies behind you to reclaim their energy.  You can also reclaim energy by absorbing any trees or rocks in the area.

Also beware — the robot sentinel will be watching for you, and if it sees you, it will try to reclaim YOUR energy!

Note that while thoroughly evil, any energy the robot sentinel takes from you or from your constructions will be redistributed across the island as trees.  We believe that this is a cynical ploy to curry favour with the deluded (albeit very ecologically aware) robot sheeple.  Make no mistake — the evil sentinel is actually evil, and must be absorbed!



Use the mouse to look around.

1/2/3 creates trees, boulders, and synthoids (robot bodies) on the square you’re looking at, respectively.  Any number of boulders may be stacked on top of each other, but a tree or synthoid on the top will end the stack.  Creating any of these objects requires energy (shown along the right side of the screen).

Right mouse button absorbs any object on the square you’re looking at, to reclaim their energy.  Objects at the top of the stack are absorbed first.

When looking at a square which contains a stack that includes a robot, Left mouse button transfers your consciousness to that robot.

Your goal is to absorb the sentinel which is standing at the top of the island.


This game is an approximation of the very early levels of The Sentinel,  a video game which is nearly 30 years old, and which doesn’t get nearly as much attention as it ought to (in part because there seems to be no contemporary implementation for people to play).  The islands in this version are randomly generated, so each play will be different, but the difficulty level doesn’t currently get anywhere close to the difficulty of the original game’s later (or even middle) levels.  The original boasted that it had 10,000 levels (procedurally generated), and had a mechanic where when you finished a level, the amount of energy you had left over determined what level you moved to next — more energy meant that you skipped further ahead in the levels.

I had about three days of implementation for this, and so didn’t have the time to tune difficulty or really ensure that the procedurally generated levels were fair (or indeed, solvable at all — I’ve once seen an island which was mostly flat, but with one huge plateau, on which the sentinel stood.  And there were not enough trees on the island to get that high).  My instinct is that in my version, the sentinel drains your energy a little too slowly.  In my mind, this is okay since I’m aiming to recreate the early levels, and don’t really want to kill players off too quickly.  :)

Similarly, there’s no sound;  the timeframe was just too tight for a game of this complexity.  If I ever return to this, sound and proper level progression are probably the key things missing.


Code & Gfx: Trevor Powell ( trevor (at) vectorstorm.org )

Game Design strongly based on The Sentinel, by Geoff Crammond.  (Geoff, if you read this, I’d be thrilled to receive an e-mail!)

Atop uses OpenGL, SDL, SDL_Image, SDL_Mixer, and GLEW.


  • 19 January, 2013: 1.0.3 release on OS X which fixes compatibility with OSX 10.6 and 10.7
  • 2 January, 2013: 1.0.1 release which fixes framework issues on OS X and window-dragging issues on Win32.
  • 31 December, 2012: Initial release (6 days, 22 hours, 32 minutes development time).