This is a work in progress, for the time being showing just the basic gameplay.

Gravi-o-roids combines elements of three of the most classic video games:

Here, a single player is set against multiple flying saucers in space, where multiple asteroids excert a gravitational force on the player's rocket ship, but not on the saucers (thanks to their advanced antigravity drives). — Mind that you cannot shoot and destroy the asteroids in this game! Asteroids are here just moving pools of gravity that also obstruct any torpedoes.
Like Computer Space it's a time-based game and you'll continue as long as you outscore the saucers.
Ever watched a sci-fi movie* where the hero dashes through an asteroid field in his spaceship? Well, it may not be that easy…

The primary purpose of this game is to explore gameplay options with multiple, dynamic gravitational attractors and to explore orbital physics with the constraints of variable frame rates that come with modern graphics update APIs. (Computing gravity normally requires a stable frame rate as this involves nonlinear functions to be computed incrementally against a constant time frame.) Chosing a suitable form of visual framing poses another, more design oriented challenge: Both Computer Space and Asteroids feature, like most video games, a marginal offscreen area (VBLANK and HBLANK), while Spacewar! wraps its toroidal space losslessly. As a noticeable offscreen area is most irritating for a gravity game (or any other force-directed game), we settle midways for just a small offscreen margin. Therefor, larger objects, like asteroids, may show up at both sides of the screen, while there's still left a small gap to emphasize any motions.


The worth of a saucer progresses by the wave (or level) as in 10, 15, 20, ….
For each wave survived you're awarded a bonus in turn for half of your balance. The bonus relates to your performance in a level and is derived from the formula 1000 + balance × 5 × wave.

How to Play

The amount of gravity excerted by an asteroid correlates with its size. As gravity adds up, it also cancels out between asteroids or between clusters of asteroids and you may still find areas of calm in rather densly populated space.

Depending on your settings ("guided shots", see the options panel below the game display) torpedoes will curve as you steer your spaceship, just like in Computer Space. It may depend on the very situation, whether to favor constant targeting over maneuvering or, if it may be wiser to let go and concentrate on navigating around any asteroids.

Do not fight gravity, rather use it in order to evade any torpedoes fired by the saucers (they are not that sophisticated in predicting your course under the influence of gravity). Gravity allows for some nice maneuvers, like sharp bends and sling shots. Orbital mechanics are an important part of the game!

Consider that you're effectively earning an extra life for each saucer shot, since progressing through the game is all about the balance. Thus, crashing your ship isn't that much of a catastrophic event as long as you manage to stay ahead of the saucers.

And, no, there aren't any power-ups or bonus items. This is (intentionally) a pure, old-school game: Your skills against the machine and time-based survival. — Like Spacewar! this game is about tactics and mastering gravity. Like Computer Space and earlier electromechanical arcade games this game is about outscoring the game mechanics for a given time segement. This also means, you're likely to die often. Mind the low gravity option, if you prefer a more moderate challenge.

*) A Not-So-Serious Note

In contemporary cinematographic terms this may be considered to be a prequel to Asteroids, which was in turn a sequel to Computer Space, which had been, of course, a soft-reboot of the Spacewar! ludomatic universe using the marvels of TTL generated images (TTLGI) for an immersive single player experience. (No frame was left untouched.) Also, it's much darker. However, this is not Pong.   ;-)

Features still to come:

Game, code and artwork  © 2016–2017 Norbert Landsteiner,