Xenotype (Commodore 64) by Sander Alsema

--- Xenotype ---

Written by Sander Alsema for the 10-liner competition 2026.

Language: Commodore 64 Basic v2

Category: PUR-80

--- Description ---

"Don't forget to write!", one of his five mothers had said to him with a tear in her eye. It was a particularly emotional farewell, that even gave Trevor a lump in his throat. Seven months later the spacecraft that carried him and his co-workers landed on Xylon, a small planet orbiting Sirius B. They were shipped to this desolate place by the Zyrcon Mining Corporation as freshly recruited employees.

Trevor's job is to harvest energy-rich crystals, as they come raining down from the sky. He does this by teleporting them directly to a cargo ship waiting in space. Normally Trevor is very good at it, but lately the quality of his work is in decline. His mind keeps wandering off to thoughts about his home planet, and the family he left behind. The poor creature is so homesick that he is in danger of losing his job.

Are you willing to assist him in his hour of need?

--- Instructions ---

All you have to do is intercept the falling crystals with your teleportation beam. Because every crystal has a different shape, the beam must have a matching frequency for it to work. There are 26 possible shapes, but you can't tell them apart with the naked eye.

For your convenience, all crystals on screen are displayed as letters.

Simply press the matching key on your keyboard to activate the beam.

You get two chances for every crystal to intercept it, and when you succeed, the next one will fall faster. When you've missed three crystals, you lose. But should you manage to intercept twenty of them, you will win!

Afterwards, press any key to play again.

--- Code Explanation ---

Line 0: Make a string that displays the alien.

Line 1: In a loop, build the vertical orientation string, the teleportation beam string, the string that erases forementioned beam and initialize the sound chip registers.

        Set background colour to black.

Line 2: Clear the screen and display the number of the letters that were hit and missed. Also display the alien.

        Pick a letter at random.

        Set the vertical position of that letter to one.

        Set the number of available shots to two.

Line 3: Set the sound volume register to maximum.

        Determine the horizontal position of the falling letter at random, to the right of the alien.

        If twenty letters have been intercepted, then set the final message string to the victory text and jump to line 9.

Line 4: If less than three letters were missed, then display the falling letter,

        Move the letter down, one position,

        If the bottom of the screen has been reached, then increase the number of letters missed and jump to line 2.

Line 5: Read the keyboard.

        If a key was pressed and there are still shots available and no sounds are being made, then display the teleportation beam,

        Set the shot-was-fired boolean,

        Decrease the number of available shots,

        Set the number of music notes to be played to two.

Line 6: Turn the sound on or off, depending on the number of music notes left to be played.

        If a shot-was-fired and the teleportation beam is where the falling letter should be and the key pressed matches the falling letter, then clear the shot-was-fired boolean,

        Increase the number of letters hit,

        Set the number of music notes to be played to ten,

        Jump to line 2.

Line 7: Play a music note by setting the pitch to a frequency depending on the number of notes left to be played.

        If a shot-was-fired then clear the shot-was-fired boolean,

        Erase the teleportation beam.

Line 8: Decrease the number of notes left to be played, when it's more than zero.

        Use a delay loop, to slow down the falling letter, depending on the number of letters hit.

        If the number of letters missed is less than three, then jump to line 4.

Line 9: Turn off the sound.

        Display "GAME OVER" and the final message.

        Clear the keyboard buffer.

        Wait until a key is pressed.

        Clear the keyboard buffer again.

        Restart the game.

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