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TI Invaders is a video game designed in 1981 exclusively for the Texas Instruments TI-99/4A home computer. The game is essentially a Space Invaders clone. It was the top-selling computer game for the TI-99/4A through at least 1982.
The object of the game is to clear the board of all invaders before they destroy all of the player's weapons or reach the bottom row.
With the joystick or keyboard, the player moves a laser base (called a missile in the manual) left and right, pressing the fire button to shoot lasers at an 11×5 grid of invaders. Shooting different invaders scores different amounts (see below). As the number of invaders dwindles, they increasingly move faster. Upon shooting the last invader, the player moves on to a bonus round before the next level. As in Space Invaders, a UFO will appear once or twice a round and travel from one end of the screen to the other. The player has the opportunity to hit it to score bonus points, the amount depending on where the UFO is hit.
There are two difficulty levels to choose from:
- Merely Aggressive (the invaders fire semi-randomly, targeting the player only sporadically)
- Downright Nasty (the invaders fire rapidly and deliberately at the player, but their point values are doubled)
Scoring is as follows:
- Lower and Lower-Middle Row - 5 or 10 points
- Middle and Top-Middle Row - 10 or 20 points
- Top Row - 15 or 30 points
- Any new invaders - additional 5 or 10 points added
- Laser shot interception - 1 point
- UFO during a round - 25-300 points (depending on where it is hit)
- UFO during bonus round - 30, 33, 36, 38, 42, 45, 50, 56, 63, 71, 83, 100, 125, 167, 250, and 500 points (for a total of up to 1689 points in all.)
After each level is cleared, there is a bonus round consisting only of one UFO. The UFO will travel slowly from one end of the screen to the other until it is hit for the first time, then it returns other way at twice its original speed. The player must track it to the other side of the screen and shoot it again, making the UFO return in the other direction again. The UFO's score value increases gradually with each hit, and the UFO gets smaller and smaller. This continues until either the player eliminates the UFO completely, or it escapes off the screen. Then the next level commences.
After earning 3,000 points the player receives an additional missile. Thereafter, at every multiple of 10,000 points, one damaged missile is repaired and again usable. (When a missile is damaged, it rolls off onto a small elevator and off to the right of the screen, and one of the extra missiles rolls onto the elevator from the left hand side and takes its place. When one is repaired, it moves from the damaged end to the extras end fully repaired.)
End of Game
When the last missile is destroyed, the closest invader to the bottom then goes down, clears away the area the extra missiles and damaged missiles were, writing "GAME OVER" in the middle of it all, then it and the rest of the remaining invaders on the screen jump up and down, as if laughing or cheering. If both the last invader on the screen and the last missile are killed at the same time (which is not an uncommon occurrence at any time in the game), the next set of invaders will immediately appear on the screen, with again the invader closest to the bottom doing the game over routine.
Also, as in Space Invaders, if any number of invaders hits the bottom row, the closest one to the missile will shoot it from the side and the game is over regardless of the number of reserve missiles left.
Comparison to Space Invaders
Many aspects of TI Invaders are similar and almost identical to Space Invaders. However there are a few differences between the games:
- The bonus round as mentioned above.
- An invader's laser shot intercepted by a player's laser shot scores 1 point.
- Though the invaders start off looking the same as their Space Invaders counterparts, on every subsequent level the lowest row of invaders disappears, the remaining rows move down, and a new set of invaders fills the top row (either a second row of the invaders already there or a whole new row of different looking invaders).