Why Galaxian Works: Comparison with an Attempted Clone

Galaxian was one of the most succesful games of the arcade golden age and a major stepping stone in the evolution of shooters.  I already talked about how it makes use of simple patterns to create flow and depth, but I want to look more carefully at the pieces and how they work together to create this experience.  Rather than look at the game in isolation, however, I'm going to compare it with another game, Cosmic Alien.

Clips of gameplay for Galaxian and Cosmic Alien, shown side-by-side.
Galaxian (left) and Cosmic Alien (right)

Superficially, Galaxian and Cosmic Alien look very similar, so much so that it's likely the latter is trying to clone the former.  But unlike Space Invaders, the cloning of which led to a virtual deluge of nearly identical gamesGalaxian proved to be more resistant to duplication.  Let's look at it piece-by-piece to see why this was.

The Armada

Galaxian and Cosmic Alien both start where Space Invaders left off, with an armada of animated aliens, all lined up and attacking the player.  

A looping GIF of the Galaxian armada.

In Galaxian, there are 46 aliens, each 11 pixels wide and separate by 4 pixels, meaning that randomly firing at the armada will miss about a quarter of the time.  Importantly, the armada is just far enough away and moving quickly enough that there is skill involved in targeting the aliens in formation.  Missing too much is not necessarily fatal, as it would be in Space Invaders, but is frustrating and requires you to fend off more alien dives.

A clilp of gameplay from Galaxian, demonstrating how it can be tricky to shoot the aliens in formation.

Cosmic Alien, by contrast, pretty much offers up the armada on a platter.  The aliens have the same sizes and separations as in Galaxian, but they're closer to the player and move more slowly, meaning that shooting them in quick succession is easy.

Sample gameplay from Cosmic Alien (1980), showing how the aliens in formation can be easily destroyed.

It's not necessarily a problem for the game to be easier (though it is), but this armada design takes away a layer of depth.  Targeting the armada is no longer a skill to develop.

The Dive Patterns

At the core of the Galaxian model are these three curves;

The dive patterns of the three colors of aliens in Galaxian (arcade version).
Galaxian dive paths.

Each alien follows its own distinctive path across the screen, with a speed optimized for flow and challenge. If they had been much slower, the aliens would have been too easy to pick off mid-dive, and if they were much faster then targeting would depend more on luck than skill (see Phoenix).  Also, the flight patterns follow simple curves that have different amounts of arc for each color of alien.  Experienced players will learn to anticipate the movements of the aliens, something that gets even more fun and challenging as their numbers increase.

The dive patterns of the three colors of aliens in Cosmic Alien (arcade, 1980).
Cosmic Alien dive paths.

Cosmic Alien's dive paths are different in significant ways, and it seems pretty clear at this point that they weren't attempting a direct clone.  While the middle pattern is very similar to the blue alien's dive in Galaxian, the other two have clear inflection points.  These inflection points appear designed to take the player off guard, particularly the third one, which mimics the middle dive pattern up until the very last second.  This change is less significant for its impact on the difficulty level than it is for the flow of the game.  Rather than learning to anticipate flowing movements of large groups of aliens, I found it more a matter of reflexes -- adjusting quickly to veering aliens and just generally avoiding them.

Why was it better to avoid the aliens rather than target them?  This brings me to the last, and I think most significant, difference between the games.

Firing Patterns

It's easy to underestimate the importance of the enemy firing patterns in shooter gameplay, especially in these early shooters when the bullets are only one or two pixels wide.  To bring out these patterns in Galaxian, I traced the enemy bullets in a playthrough clip (2x speed).

A clip of Galaxian gameplay at 2x speed with the bullets traced out.  Most of the bullets move diagonally, despite being vertical sprites.

There's a lot going on here that you wouldn't necessarily notice when playing.  For one thing, even though the bullet sprites point downward, they actually follow diagonal paths, always veering slightly in the direction of the player.  This subtle bit of artificial intelligence is just enough to make the game feel like it's responding to the player without them being completely aware of why.

Another important thing to notice is that the bullets are spread out across the field.  Aliens begin firing early in their dive pattern regardless of where the player is along the horizontal, leaving a curtain of bullets to navigate, even if you manage to avoid the alien itself.  My favorite moments in Galaxian are when I manage to duck and weave through the middle of several curtains in a row.

Finally, bullets are never fired more than about 90 pixels above the player, a distance it takes about 20 frames for the bullets to cross.  This is just about right if you're trying to give the player a fair chance to react.

Contrast this to Cosmic Alien.  I didn't bother to trace out the bullet patterns, for reasons that should be clear from the following montage:

Clips of Cosmic Alien gameplay spliced together to show the alien bullet patterns and firing behavior.

Here, the aliens function more like dive bombers, shooting only when they're directly over your ship.  They fire multiple shots, but in such a small clump that there's no possibility of maneuvering between them.  The lack of spacing between bullets removes yet another layer of depth, while the dive-bomber style of enemy fire motivates the player to avoid the action.

Difficulty curve

Galaxian is notable for its shallow difficulty curve.  The developers were wary of creating a difficulty spike, so they left the armada size and distance to the player the same, slowly increasing the rate of dives.  I think the curve is a little too shallow, but the design decision to avoid difficulty spikes was the more important one.  Sudden changes in difficulty are not just frustrating, but also tend to reduce immersion by suddenly making the player more aware that they're playing a game.  

Cosmic Alien's difficulty is not so much steep as it is jagged.  Every few rounds, the player moves closer to the armada in a large step.

Gameplay in the fifth stage of Cosmic Alien (1980), demonstrating how the developers increased the difficulty.

There are a lot of problems with this.  Because the player is moving so close to the armada, there is very little space for the enemy fire, and the game becomes more about dodging the aliens themselves than their bullets.  Even if this doesn't always spike the difficulty, it does cause a sudden change in the complexion of the game.  

Also, there's no clear in-game reason why the player would keep moving closer, so the player is forcefully broken from the game world with the realization that the designer is trying to make things harder on them.  Even in games as simple as Galaxian or Cosmic Alien,  in-game consistency and a sort of "suspension of disbelief" can be a key factor in engaging the player.

But I think this also provides a good example of a more general problem in action game design.  By moving the player closer to the armada, they give the player significantly less time to react to alien movements.  When you design your difficulty curve to simply demand more of a player's reaction time, you limit how much and how quickly a player can improve.  There is certainly evidence that playing more video games can improve your reaction time, but it's a slow process.  

By contrast, games like Pac-Man or Frogger allowed players to improve through pattern recognition, a form of learning that humans are especially adept atGalaga, the even more successful sequel to Galaxian, would put greater emphasis on pattern recognition than its predecessor, and I have no doubt that this played a large role in its success.

The Big Picture

Galaxian is a much more nuanced game than it might appear at first glance.  Developers who tried to imitate it, like Universal did with Cosmic Alien, would make small changes and end up with a completely different animal.  Overall, I found Galaxian to be an entrancing experience with great staying power, while Cosmic Alien alternated between irritating and boring me.

That's not to say that all attempts to follow the Galaxian model were a failure, however.  In my next shooter gallery, I'll look at some other similar games from the golden age.


  1. Such a fun and informative read!

    A similar deep dive of Frogger and it's clones would be a real treat. Be sure to include a look at the 8-bit home systems - there were some very innovative games there that used Frogger as a starting point (i.e. Preppie I and II).

    1. Thanks! I still have a little ground to cover before Frogger, but it’s definitely in the plans.

  2. Hello! I love the presentation of this blog. It's extremely useful to have gifs for quick reference on these early games and you do very well in charting the gradual design changes from clone to cornerstone. There's a lot of interesting steps towards something like Scramble for instance that I hope you'll cover.

    One little detail that's interesting historically is that Kazunori Sawano, who created Galaxian, placed the dive bombing mechanic on a movie he had seen called "Admiral Yamamoto and the Allied Fleets" which can be found on Youtube. It was an old movie even at the time the game was being made, but it's interesting to compare the patterns.


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