Game 14 Unit 24 of 32 1 hr learning time

Power-Up: Shield

Collect a shield to absorb one hit without losing a life — a defensive power-up with HUD indicator.

75% of Blockstorm

Mark as complete Completed!

The double shot improves offence. The shield improves defence. When collected, it absorbs one hit — a bomb or direct contact that would normally cost a life is negated and the shield is consumed. The HUD shows a shield icon when active, giving the player clear visual feedback about their protection status.

The Program

5 REM === POWER-UP: SHIELD ===
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 tw = 5
24 LET pw = 0: LET sh = 0
25 DIM e(20): DIM r(20): DIM t(20): DIM h(20)
27 DIM b(2): DIM c(2): DIM d(2)
28 DIM m(3): DIM n(3): DIM o(3)
40 REM === load wave ===
42 RESTORE 900
44 FOR i = 1 TO wv - 1
46 READ ne, nr, sp
48 FOR j = 1 TO ne: READ a, a, a, a: NEXT j
50 NEXT i
52 READ ne, nr, sp
54 FOR i = 1 TO ne
56 READ e(i), r(i), t(i), h(i)
58 NEXT i
60 LET fx = 10: LET fy = 2: LET fd = 1
62 LET px = 15: LET py = 20
64 LET tk = 0
66 FOR i = 1 TO 2: LET d(i) = 0: NEXT i
68 FOR i = 1 TO 3: LET o(i) = 0: NEXT i
70 CLS
72 GO SUB 600
75 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 GO SUB 450
125 GO SUB 550
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 FOR i = 1 TO 2
354 IF d(i) = 0 THEN GO TO 396
356 PRINT AT c(i), b(i); " "
358 LET c(i) = c(i) - 1
360 IF c(i) < 1 THEN LET d(i) = 0: GO TO 396
362 REM check hit
364 LET ht = 0
366 FOR j = 1 TO ne
368 IF h(j) <= 0 THEN GO TO 385
370 LET sx = fx + e(j): LET sy = fy + r(j)
372 IF b(i) = sx AND c(i) = sy THEN LET ht = j: GO TO 386
385 NEXT j
386 IF ht = 0 THEN PRINT AT c(i), b(i); INK 7; CHR$ 148: GO TO 396
388 LET d(i) = 0
390 LET h(ht) = h(ht) - 1
391 IF h(ht) <= 0 THEN GO SUB 510: GO TO 396
392 PRINT AT fy + r(ht), fx + e(ht); INK 7; CHR$ (143 + t(ht)): BEEP 0.01, 10
394 PAUSE 2: PRINT AT fy + r(ht), fx + e(ht); INK 6; CHR$ (143 + t(ht))
396 NEXT i
398 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
426 IF fy + nr > 19 THEN GO TO 700
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
439 IF t(i) = 3 THEN LET ci = 6
440 IF t(i) = 4 THEN LET ci = 3
442 PRINT AT sy, sx; INK ci; CHR$ (143 + t(i))
445 NEXT i
447 RETURN
450 REM === move bombs ===
452 FOR i = 1 TO 3
454 IF o(i) = 0 THEN GO TO 480
456 PRINT AT n(i), m(i); " "
458 LET n(i) = n(i) + 1
460 IF n(i) > 21 THEN LET o(i) = 0: GO TO 480
462 IF m(i) = px AND n(i) = py THEN GO SUB 530: LET o(i) = 0: GO TO 480
464 PRINT AT n(i), m(i); INK 2; CHR$ 153
480 NEXT i
484 FOR i = 1 TO ne
486 IF h(i) <= 0 OR t(i) <> 4 THEN GO TO 496
488 IF INT (RND * 30) <> 0 THEN GO TO 496
490 FOR j = 1 TO 3
492 IF o(j) = 0 THEN LET m(j) = fx + e(i): LET n(j) = fy + r(i) + 1: LET o(j) = 1: LET j = 3
494 NEXT j
496 NEXT i
498 RETURN
500 REM === draw player ===
505 PRINT AT py, px; INK 7; CHR$ 152
508 RETURN
510 REM === enemy destroyed ===
512 LET sx = fy + r(ht): LET sy = fx + e(ht)
514 PRINT AT sx, sy; INK 2; CHR$ 149
516 BEEP 0.02, -5: BEEP 0.02, -10
518 LET pt = 10
519 IF t(ht) = 2 THEN LET pt = 25
520 IF t(ht) = 3 THEN LET pt = 50
521 IF t(ht) = 4 THEN LET pt = 30
522 LET sc = sc + pt
524 IF sc > hi THEN LET hi = sc
528 RETURN
530 REM === player hit ===
532 IF sh = 1 THEN LET sh = 0: BEEP 0.05, 5: RETURN
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
550 REM === check power-ups ===
552 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 LET sc = sc + wv * 50
666 BEEP 0.1, 12: BEEP 0.1, 16: BEEP 0.2, 19
668 GO SUB 600
670 PAUSE 50
672 LET wv = wv + 1
674 IF wv > tw THEN GO TO 750
676 GO TO 40
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; "Wave: "; wv
725 PRINT AT 14, 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: LET wv = 1
742 LET pw = 0: LET sh = 0
745 GO TO 20
750 REM === game complete ===
755 CLS
760 PRINT AT 6, 7; INK 7; BRIGHT 1; "CONGRATULATIONS!"
765 PRINT AT 8, 5; INK 6; "All "; tw; " waves defeated!"
770 PRINT AT 10, 7; INK 7; "Final score: "; sc
775 PRINT AT 14, 6; INK 7; "Press any key"
780 PAUSE 0
785 GO TO 700
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
900 REM === WAVE DATA ===
902 REM wave 1: 8 drones, 1 row, speed 4
904 DATA 8, 1, 4
906 DATA 0,0,1,1, 2,0,1,1, 4,0,1,1, 6,0,1,1, 8,0,1,1, 10,0,1,1, 12,0,1,1, 14,0,1,1
910 REM wave 2: 10 drones, 2 rows, speed 4
912 DATA 10, 2, 4
914 DATA 0,0,1,1, 2,0,1,1, 4,0,1,1, 6,0,1,1, 8,0,1,1, 0,1,1,1, 2,1,1,1, 4,1,1,1, 6,1,1,1, 8,1,1,1
920 REM wave 3: 10 mixed, 2 rows, speed 3
922 DATA 10, 2, 3
924 DATA 0,0,1,1, 2,0,1,1, 4,0,1,1, 6,0,1,1, 8,0,1,1, 1,1,2,1, 3,1,1,1, 5,1,2,1, 7,1,1,1, 9,1,1,1
930 REM wave 4: 12 mixed, 3 rows, speed 3
932 DATA 12, 3, 3
934 DATA 4,0,1,1, 6,0,1,1, 3,1,1,1, 5,1,2,1, 7,1,1,1, 2,2,1,1, 4,2,1,1, 6,2,1,1, 8,2,1,1, 1,1,1,1, 9,1,1,1, 5,0,3,2
940 REM wave 5: 14 mixed with bombers, speed 2
942 DATA 14, 3, 2
944 DATA 0,0,1,1, 2,0,1,1, 4,0,4,1, 6,0,1,1, 8,0,4,1, 10,0,1,1, 12,0,1,1, 0,1,2,1, 4,1,3,2, 8,1,2,1, 12,1,1,1, 2,2,1,1, 6,2,1,1, 10,2,1,1

How It Works

The shield icon (UDG H, CHR$ 151) drops from a destroyed enemy, just like the double-shot power-up. The same drop mechanism, the same falling behaviour, the same collection check. The difference is the type: the drop routine randomly chooses between double-shot and shield.

The sh variable tracks whether a shield is active. When the shield is collected, sh is set to 1.

Line 532 in the player hit routine checks sh before applying damage:

IF sh = 1 THEN LET sh = 0: BEEP 0.05, 5: RETURN

If the shield is active, it is consumed (sh = 0), a short tone plays, and the routine returns without decreasing lives. The player survives the hit. The next hit, with no shield, will cost a life as normal.

The HUD update shows a shield icon (UDG L, CHR$ 155) when sh is 1 and a blank space when sh is 0. The player can glance at the HUD to know whether they have protection.

One Active Power-Up

Only one power-up can be active at a time. If the player has a shield and collects a double shot, the double shot replaces the shield. This keeps the system simple: one variable for the current power-up type, one set of rules for its effect. With two simultaneous power-ups, the code complexity doubles and the HUD needs more space.

The single-power-up rule also creates meaningful choices. Do you collect the shield when bombs are falling? Or skip it and wait for a double shot to clear the wave faster? Each power-up has a different value depending on the situation.

Shield vs Extra Life

A shield and an extra life both prevent death, but they feel different. An extra life is permanent — you can spend it on any future mistake. A shield is immediate — it protects against the next hit only. The shield adds tactical depth: the player might take risks they would otherwise avoid, knowing they have one free hit. It changes behaviour without changing the rules.

Try This

Visual shield. When the shield is active, draw the ship in a different colour — cyan instead of white. The player can see their protection without checking the HUD. Change the colour back when the shield is consumed.

Shield duration. Instead of absorbing one hit, make the shield last for 100 game ticks. It absorbs any number of hits during that window, then expires. This is more generous but creates a timed power-up feel.