Bill Kendrick's Entries
for the NOMAM 2019

About the program

Download

• missile10.atr - Bootable disk image, with MyDOS, TurboBASIC XL (auto-loaded at boot), and the game program as tokenized BASIC (auto-loaded by TurboBASIC).
• missile10.txt - ASCII source code, as fed through my PHP script that converts to ATASCII and shoves into an ATR disk image for auto-ENTER-ing by TurboBASIC XL.

How the code works

Line 10

• Sets up arrays for:
  • incoming missiles
    • MA = active
    • MX & MY = position
    • MDX = X delta (angle)
  • explosions
    • EA = active,
    • EX & EY = position
    • ER = radius
    • EDR = radius delta (getting larger, or smaller?)
• Sets graphics mode (80x48, 4 colors, with a text window)
• Sets 3rd color, also used by text window (color register itself is used for life/energy/damage)
• Clears all missiles and explosions (FOR...NEXT)
• Sets cursor position (~center of screen)
• Begins the main loop (DO...LOOP)
• Sets color for drawing missiles
• Begins missile handling loop (FOR...NEXT)

Line 20

• Draws and moves missile, if active (MA)
• Begins missile-explosion collision loop (FOR...NEXT)
• Checks basic rectangle bounding-box collision

(Oops, there's no line 30)

LINE 40

• Checks circular collision (slower, hence only done if within rectangle, in line 20)
• Ends missile-explosion collision loop

Line 50

• Deactivates and erases missile, if collided with an explosion (H=1), or out of bounds (MX/MY tests)
• If hit an explosion, creates a new explosion (GOSUB 1000) and increases score (GOSUB 2000)

Line 60

• Checks if missile hit the ground/base
• Decreases energy, if so
• Ends game if energy has run out

Line 70

• If the missile is not already active (ELSE...ENDIF), randomly activates it
• Ends missile handling loop
• Grabs joystick state (S)
• Erases targetter

Line 80

• Moves targetter, based on joystick input (X,Y)
• Keeps joystick within screen bounds (plus margin for explosion radius; also makes it harder!)
• Draws targetter

Line 90

• Handles Fire button; creates new explosion at targetter location (GOSUB 1000)
• Begins explosion handling loop
• If explosion is active (EA)...
• Draw, or erase a circle at the current radius (depending on if it's growing or shrinking; EDR)
• If it's shrinking, and has shrunk all the way, deactivate the explosion
• Otherwise, if it's growing, and hit the maximum radius, begin shrinking
• Ends explosion handling loop
• Ends the main loop

Line 1000 - Explosion-creation subroutine

• Find an open explosion slot
• Play some sound if one has been found, while checking (kinda silly method)
• If a slot was found, set its location (EX,EY), radius (ER), and direction (growing) (EDR)

Line 2000 - Score subroutine

• Increase the score
• Show the score (in the text window)
• Have room to do more here, like flash the screen, play a sound, etc.

About the program

Watch it on YouTube

Download

• amenbreak.atr - Bootable disk image, with MyDOS, TurboBASIC XL (auto-loaded at boot), and the program as tokenized BASIC (auto-loaded by TurboBASIC).

How the code works

Line 10

• Sets up arrays for the various voices and instruments in the drum kit, named based on the drum tabs:
  • C$ = Crash cymbal
  • R$ = Ride cymbal
  • S$ = Snare drum
  • B$ = Bass drum
• Fills in the crash cymbal (only one hit), using the Atari BASIC (and hence TurboBASIC XL) trick for filling a string
• Prints some credits for the song

Line 15

• Prints more credits
• Sets default tempo (5, or T=3) and length (all four bars = all 64 quarter beats(?))
• Prompts for tempo and bars, does the math to convert user input to usable values

Line 20

• Fills in the ride cymbal (constant hit, except for two places), again using the BASIC string-fill trick
• Fills in (most of) the snare drum

Line 30

• Fills in the rest of the snare drum
• Fills in the bass drum

Line 40

• Begins the loop through all beats (of however many bars chosen)
• Sets volume variables for most voices/instruments (all but bass), based on what's in the strings

Line 50

• Sets volume variable for bass drum, as above
• Begins loop to play instruments (duration depends on 'tempo')
• Plays each sound (you may have ideas for better pitches and distortions to use!)

Line 60

• Reduces volume variable for each voice/instrument (stopping at 0)

Line 70

• Ends loop to play instruments

(No line 80)

Line 90

• Ends loop through all the beats
• Goes back to Line 40, to start over (infinite loop)