Resolution

From the information I was able to find it appears the original Space Invaders ran at a resolution of 224x260 pixels. This is quite small in a web browser of todays standards so I will double it to 448x520 pixels.

Controls

The player controls a mobile laser turret.

Move left/right. The left and right arrow keys will be used to move the players mobile laser turret.

Fire button. The space bar will fire the players cannon. The player is only allowed to have one shot in play at a time.

Lives

The player will start with three lives. A new life is awarded every 1500 points.

A life is lost when the following events occur.

• The player collides with an alien bullet.

Space Invaders

There are three different type of space invaders. Other than their size and appearance they behave identically.

The space invaders will slowly march to the right hand side of the screen. When the right most invader reaches to side of the screen the entire formation will descend one row and march back the opposite direction. The space invaders will continue in this fashion until the player has shot them all down or they reach the bottom of the screen.

Occasionally a space invader who is at the bottom of his column will open fire on the player. If a players shot and a space invaders shot collide one of the shots will be randomly canceled out and the other shot continues on it's way. There are two types of shots the space invaders can fire. Other than visual styling I can see no difference in how the two shot behave.

Flying saucers

Occasionally a red flying saucer will randomly appear on one side of the top of the screen. The flying saucer will then travel in a straight line to the other side of the screen. Shooting down the flying saucer will result in a random amount of bonus points.

Bunkers

There are four bunkers positioned on the screen. The bunkers can absorb shots fire by both the player and the space invaders. The bunkers are not invulnerable and will slowly be worn away. The bunkers appear to use pixel perfect collision detection and a pattern is overlaid at the point of impact that determines which pixels get erased from the bunker.

If a space invader collides with a bunker it will destroy all of the bunker that it comes into contact with.

Rounds

Each round starts with a grid formation of elven space invaders across by five space invaders deep. The top most row is made of the squid space invader, the next two rows made up of the crab space invader and the final two rows are made up of the octopus space invader.

A round is completed when the player has successfully shot down all the space invader in the grid formation. Upon completing a round a new wave of aliens will start their assault on Earth but one row closer than the previous round.

If the space invaders manage to land on the bottom of the screen the game is lost.

Scoring

• Space invader (Octopus): 10 points
• Space invader (Crab): 20 points
• Space invader (Squid): 30 points
• Space invader (Flying saucer): 50 to 300 points