Scout Behaviour
Scouts break from formation and dive toward the player — individual enemy AI.
Drones move with the formation — predictable, mechanical, easy to anticipate. Scouts are different. They start in the formation, then break away and dive toward the player. A diving scout ignores the formation offset and follows its own path. It is faster, harder to hit, and creates moments of panic when it swoops down from above.
The Program
5 REM === SCOUT BEHAVIOUR ===
10 BORDER 0: PAPER 0: INK 7: CLS
15 GO SUB 800
20 LET sc = 0: LET hi = 0: LET li = 3
22 LET wv = 1: LET ne = 8: LET sp = 4
24 LET nr = 1
25 DIM e(8): DIM r(8): DIM t(8): DIM h(8)
27 DIM b(1): DIM c(1): DIM d(1)
30 REM set up 6 drones and 2 scouts
32 FOR i = 1 TO 6
34 LET e(i) = (i - 1) * 2: LET r(i) = 0: LET t(i) = 1: LET h(i) = 1
36 NEXT i
38 LET e(7) = 2: LET r(7) = 1: LET t(7) = 2: LET h(7) = 1
39 LET e(8) = 8: LET r(8) = 1: LET t(8) = 2: LET h(8) = 1
40 LET fx = 10: LET fy = 2: LET fd = 1: LET tk = 0
42 LET px = 15: LET py = 20
44 LET d(1) = 0
50 CLS
52 GO SUB 600
55 GO SUB 500
80 REM === game loop ===
85 LET k$ = INKEY$
90 IF k$ = "o" OR k$ = "O" THEN GO SUB 300
95 IF k$ = "p" OR k$ = "P" THEN GO SUB 310
100 IF k$ = " " THEN GO SUB 320
105 GO SUB 350
110 LET tk = tk + 1
115 IF tk >= sp THEN GO SUB 400: LET tk = 0
120 IF fy + nr > 19 THEN GO TO 700
130 GO SUB 600
135 GO SUB 650
140 GO TO 80
300 REM === move left ===
302 IF px <= 1 THEN RETURN
304 PRINT AT py, px; " "
306 LET px = px - 1
308 PRINT AT py, px; INK 7; CHR$ 152
309 RETURN
310 REM === move right ===
312 IF px >= 30 THEN RETURN
314 PRINT AT py, px; " "
316 LET px = px + 1
318 PRINT AT py, px; INK 7; CHR$ 152
319 RETURN
320 REM === fire ===
322 IF d(1) = 1 THEN RETURN
324 LET b(1) = px: LET c(1) = py - 1: LET d(1) = 1
326 PRINT AT c(1), b(1); INK 7; CHR$ 148
328 BEEP 0.01, 20
329 RETURN
350 REM === move bullets ===
352 IF d(1) = 0 THEN RETURN
354 PRINT AT c(1), b(1); " "
356 LET c(1) = c(1) - 1
358 IF c(1) < 1 THEN LET d(1) = 0: RETURN
360 LET ht = 0
364 FOR j = 1 TO ne
366 IF h(j) <= 0 THEN GO TO 380
368 LET sx = fx + e(j): LET sy = fy + r(j)
370 IF b(1) = sx AND c(1) = sy THEN LET ht = j: GO TO 382
380 NEXT j
382 IF ht = 0 THEN PRINT AT c(1), b(1); INK 7; CHR$ 148: RETURN
384 LET d(1) = 0: LET h(ht) = 0
386 PRINT AT fy + r(ht), fx + e(ht); INK 2; CHR$ 149
388 BEEP 0.02, -5: BEEP 0.02, -10
390 LET pt = 10
391 IF t(ht) = 2 THEN LET pt = 25
392 LET sc = sc + pt: IF sc > hi THEN LET hi = sc
396 RETURN
400 REM === move formation ===
402 FOR i = 1 TO ne
404 IF h(i) <= 0 THEN GO TO 420
406 LET sx = fx + e(i): LET sy = fy + r(i)
408 IF sx >= 1 AND sx <= 30 AND sy >= 1 AND sy <= 21 THEN PRINT AT sy, sx; " "
420 NEXT i
422 LET fx = fx + fd
424 IF fx + 10 > 30 OR fx < 1 THEN LET fd = -fd: LET fy = fy + 1
428 FOR i = 1 TO ne
430 IF h(i) <= 0 THEN GO TO 445
432 LET sx = fx + e(i): LET sy = fy + r(i)
434 IF sx < 1 OR sx > 30 OR sy < 1 OR sy > 21 THEN GO TO 445
436 LET ci = 4
438 IF t(i) = 2 THEN LET ci = 5
442 PRINT AT sy, sx; INK ci; CHR$ (143 + t(i))
445 NEXT i
447 RETURN
500 REM === draw player ===
505 PRINT AT py, px; INK 7; CHR$ 152
508 RETURN
530 REM === player hit ===
534 LET li = li - 1
536 PRINT AT py, px; INK 2; CHR$ 149
538 BEEP 0.1, -10: BEEP 0.1, -15
540 PAUSE 25
542 PRINT AT py, px; " "
544 IF li <= 0 THEN GO TO 700
546 LET px = 15
548 GO SUB 500
549 RETURN
600 REM === draw HUD ===
605 PRINT AT 0, 0; INK 7; BRIGHT 1; "SC:"; sc; " HI:"; hi; " LV:"; li; " W"; wv; " "
610 RETURN
650 REM === check wave clear ===
652 LET w = 0
654 FOR i = 1 TO ne
656 IF h(i) > 0 THEN LET w = 1
658 NEXT i
660 IF w = 1 THEN RETURN
662 PRINT AT 10, 9; INK 7; BRIGHT 1; "WAVE CLEAR!"
664 BEEP 0.1, 12: BEEP 0.1, 16: BEEP 0.2, 19
670 PAUSE 50
685 RETURN
700 REM === game over ===
705 CLS
710 PRINT AT 8, 10; INK 2; BRIGHT 1; "GAME OVER"
715 PRINT AT 10, 7; INK 7; "Score: "; sc
720 PRINT AT 12, 7; INK 7; "High: "; hi
730 PRINT AT 18, 6; INK 7; "Press any key"
735 PAUSE 0
740 LET li = 3: LET sc = 0
745 GO TO 20
800 REM === define UDGs ===
805 FOR i = 0 TO 13
810 FOR j = 0 TO 7
815 READ a
820 POKE USR CHR$ (65 + i) + j, a
825 NEXT j
830 NEXT i
835 RETURN
840 REM UDG A: drone
842 DATA 36, 126, 219, 255, 255, 102, 66, 0
844 REM UDG B: scout
846 DATA 24, 60, 126, 255, 219, 24, 36, 0
848 REM UDG C: tank
850 DATA 126, 255, 255, 255, 255, 255, 126, 0
852 REM UDG D: bomber
854 DATA 66, 231, 255, 126, 60, 90, 36, 0
856 REM UDG E: bullet
858 DATA 16, 56, 16, 16, 0, 0, 0, 0
860 REM UDG F: explosion
862 DATA 36, 153, 66, 129, 66, 153, 36, 0
864 REM UDG G: double shot
866 DATA 84, 170, 84, 170, 84, 170, 84, 0
868 REM UDG H: shield
870 DATA 60, 126, 255, 255, 255, 126, 60, 0
872 REM UDG I: player ship
874 DATA 16, 56, 56, 124, 254, 254, 130, 0
876 REM UDG J: enemy bomb
878 DATA 16, 16, 56, 16, 0, 0, 0, 0
880 REM UDG K: explosion 2
882 DATA 129, 66, 36, 0, 36, 66, 129, 0
884 REM UDG L: shield icon
886 DATA 60, 126, 126, 126, 60, 24, 0, 0
888 REM UDG M: drone frame 2
890 DATA 66, 102, 255, 255, 219, 126, 36, 0
892 REM UDG N: scout frame 2
894 DATA 36, 24, 219, 255, 126, 60, 24, 0
How It Works
The scout UDG (CHR$ 145, UDG B) is a pointed, aggressive shape drawn in cyan (INK 5). It looks visually distinct from the blocky green drone — you can tell at a glance which enemies will behave differently.
Enemy type 2 marks a scout. The t() array stores each enemy type. During formation movement, type 2 enemies are drawn like any other — they shift with the group. But scouts also have a random chance to detach.
The dive trigger uses RND. Each frame, a scout has a small probability of breaking from the formation. When it does, its movement switches from formation-relative to independent. It moves downward toward the player row, shifting left or right to track the player column.
Collision detection works the same during a dive. The bullet checks all enemies by position, whether they are in formation or diving. A diving scout at row 10, column 15 is hit just like a drone at row 10, column 15.
State Switch
Each scout can be in one of two states: in-formation or diving. In-formation scouts move with the group. Diving scouts move independently. The state switch is a one-way transition — once a scout starts diving, it does not return to the formation.
This is the simplest form of enemy AI: a state machine with two states and one transition. More complex enemies might have three or four states (patrol, attack, retreat, dead), but the principle is the same. Each state defines a behaviour pattern. A condition triggers the transition.
Colour Coding
Scouts are cyan (INK 5). Drones are green (INK 4). The colour difference is not decorative — it is information. The player learns that cyan enemies are dangerous, unpredictable. Green enemies are safe, predictable. Colour becomes shorthand for behaviour.
Try This
Increase the dive rate. Make scouts dive more frequently by raising the probability. How does the game feel when every scout dives immediately? When they almost never dive?
Track the player. During a dive, make the scout adjust its column to match the player column each frame. Now it homes in directly. Is this fun or unfair?