Routines
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27176: Main game loop: Process keyboard input and move Magic Knight, enter menus or execute other command
27176 CALL 34821 Update Magic Knight's current frame based on x-coordinate
27179 LD (65528),A Store frame number at 65528...
27182 LD (25390),A ...and in Magic Knight's current data
27185 XOR A Set A to zero (Magic Knight) and...
27186 CALL 39224 ...draw Magic Knight (erase old frame and draw new frame)
This entry point is used by the routines at 26906, 27168, 31636, 32035, 32194, 32258, 32390, 32655, 33312, 33593 and 33663.
27189 CALL 29763 Run checks and updates (Magic Knight's current room and room-specific routines)
27192 CALL 27495 Handle Magic Knight's fall
27195 LD A,127 Reset bit 7 in A to select the keyboard half-row SPACE - B
27197 IN A,(254) Read the keyboard
27199 RRA Reset carry flag if SPACE pressed, else set it
27200 JR C,27213 SPACE was not pressed, so skip ahead to 27213
27202 LD A,254 Reset bit 0 in A to select the keyboard half-row SHIFT - V
27204 IN A,(254) Read the keyboard
27206 RRA Reset carry flag if SHIFT pressed, else set it
27207 LD HL,43450 Point HL at "BREAK KEY PRESSED" text
27210 JP NC,35101 If SHIFT was pressed (i.e. SHIFT-SPACE, or BREAK) jump to "game over" window routine and exit
27213 CALL 27666 Kill Magic Knight's x-velocity if he cannot horizontally pass through a block beside him
27216 CALL 37876 Capture keyboard/joystick input into A
27219 BIT 0,A If "left" pressed then...
27221 JP NZ,27307 Skip ahead to move left subroutine
27224 BIT 1,A If "right" pressed then...
27226 JP NZ,27358 Skip ahead to move right subroutine
27229 BIT 2,A If "up" pressed then...
27231 JP NZ,27374 Skip ahead to jump subroutine
27234 BIT 3,A Check for "down" pressed
The following three bytes are set to zero (NOP) by the instructions between 26633 and 26640. This disables the conditional jump to the cheat / debug routine at 35420 (see trivia).
27236 NOP
27237 NOP
27238 NOP
27239 BIT 4,A If "fire" pressed then...
27241 JP NZ,27301 Skip ahead to 27301
27244 LD A,(65528) Set Magic Knight's current frame to stored value...
27247 LD (25390),A ...
27250 XOR A Set A to zero (Magic Knight) and...
27251 CALL 39224 ...draw Magic Knight (erase old frame and draw new frame)
27254 LD A,(23560) Load A with last pressed key (LAST K system variable)
27257 OR A If last key pressed is null (i.e. key NOT pressed)...
27258 JP Z,27189 ...then jump into main game loop (process keyboard input and move Magic Knight, enter menus or execute other command)
27261 LD HL,41811 Point HL at string of keyboard shortcuts for commands
27264 LD B,A Load index of key pressed into B
27265 LD C,0 Set C (index of command shortcut) to zero initially
27267 LD A,(HL) Load command shortcut from table at 41811 into A
27268 OR A If A is zero (i.e. we have reached the last command shortcut in the table)...
27269 JP Z,27189 ...then jump into main game loop (process keyboard input and move Magic Knight, enter menus or execute other command)
27272 CP B If key pressed matches current command shortcut...
27273 JP Z,27280 ...then skip ahead to 27280
27276 INC C Increase C to advance to next command shortcut to test
27277 INC HL Advance pointer to next shortcut
27278 JR 27267 Loop back to 27267 for next shortcut
27280 CALL 37472 Wait for keyboard to be released
27283 LD A,C Load double the index of command shortcut chosen into BC...
27284 ADD A,A ...
27285 LD B,0 ...
27287 LD C,A ...
27288 LD HL,41827 Point HL at table of routine start addresses for Magic Knight's main menu commands
27291 ADD HL,BC Add double index of this command's entry as offset, so HL now points at address in table of chosen command
27292 LD A,(HL) Load address into HL...
27293 INC HL ...
27294 LD H,(HL) ...
27295 LD L,A ...
27296 XOR A Clear last pressed key (LAST K system variable)...
27297 LD (23560),A ...
27300 JP (HL) Execute the command, then return to game
Fire pressed
27301 CALL 37486 Wait for fire button / key to be released
27304 JP 31153 Display and handle main in-game menu, execute selected command and return to game
Left pressed
27307 LD HL,23470 If Magic-Knight-can't-move-left flag is set...
27310 BIT 0,(HL) ...
27312 JP NZ,27254 ...then loop back to start of keyboard check routine
27315 LD HL,34824 Load HL with 34824 (left-facing version of update Magic Knight's current frame routine)
27318 EX AF,AF' Switch AF and AF'
27319 LD A,254 Set Magic Knight's x-velocity to minus 2...
27321 LD (25391),A ...
27324 LD (27405),A Prepare to set Magic Knight's x-velocity to minus 2
27327 LD (34822),HL Set instruction at 34821 to jump to 34824 (left-facing version of update Magic Knight's current frame routine)
27330 EX AF,AF' Switch AF and AF' (A now holds pressed controls bitmap)
27331 BIT 2,A If "up" was also pressed...
27333 JR NZ,27378 ...then skip ahead to 27378 (jumping subroutine)
27335 XOR A Set Magic Knight's current y-velocity to zero...
27336 LD (25392),A ...
27339 CALL 34821 Update Magic Knight's current frame based on x-coordinate...
27342 LD (25390),A ...
27345 LD (65528),A Store frame number at 65528
27348 XOR A Set A to zero (Magic Knight) and...
27349 CALL 39224 ...draw Magic Knight (erase old frame and draw new frame)
27352 CALL 27495 Handle Magic Knight's fall
27355 JP 27254 Loop back for next key / control press
Right pressed
27358 LD HL,23470 If Magic-Knight-can't-move-right flag is set...
27361 BIT 1,(HL) ...
27363 JP NZ,27254 ...then loop back to start of keyboard check routine
27366 LD HL,34838 Load HL with 34838 (right-facing version of update Magic Knight's current frame routine)
27369 EX AF,AF' Switch AF and AF'
27370 LD A,2 Jump to 27321, setting Magic Knight's x-velocity to 2...
27372 JR 27321 ...
Up pressed
27374 XOR A Prepare to set Magic Knight's x-velocity to zero...
27375 LD (27405),A ...
27378 LD HL,41859 Point HL at start of Magic Knight's y-velocities sequence table
27381 LD (41857),HL Store current position in Magic Knight's y-velocities sequence table at 41857
27384 LD A,(25388) Load Magic Knight's current y-coordinate into A
27387 CP 8 If y-coordinate is less than 8...
27389 JP C,27468 ...then jump to 27468 (exit loop as Magic Knight can't get any higher!)
27392 LD HL,(41857) Load HL with current position in Magic Knight's y-velocities sequence table
27395 LD A,(HL) Load the current y-velocity in the sequence into A
27396 NEG Negate (as Magic Knight is jumping upwards)
27398 OR A If A is zero...
27399 JR Z,27468 ...jump to 27468 (exit loop as we have reached the end of the sequence)
27401 LD (25392),A Load A into Magic Knight's y-velocity
The operand of the instruction at 27404 represents the x-velocity value stored previously. This is modified by the instruction at 27375.
27404 LD A,0 Set Magic Knight's x-velocity...
27406 LD (25391),A ...
27409 CALL 27666 Kill Magic Knight's x-velocity if he cannot horizontally pass through a block beside him
27412 LD A,(25391) Load Magic Knight's x-velocity into B...
27415 LD B,A ...
27416 LD A,(23470) Load Magic Knight movement flags into A
27419 XOR B Check:
27420 CP 255 If x-velocity is -2 (left), and Magic Knight can't move left...
27422 JP Z,27480 ...then jump ahead to 27480
27425 CP 253 If x-velocity is -2 (left), and Magic Knight can't move left or right...
27427 JP Z,27480 ...then jump ahead to 27480
27430 CP 1 If x-velocity is +2 (right), and Magic Knight can't move left or right...
27432 JP Z,27480 ...then jump ahead to 27480
27435 OR A If x-velocity is +2 (right), and Magic Knight can't move right...
27436 JP Z,27480 ...then jump ahead to 27480
27439 CALL 34821 Update Magic Knight's current frame based on x-coordinate...
27442 LD (25390),A ...
27445 LD (65528),A Store frame number at 65528
27448 CALL 27809 Kill Magic Knight's jump if he cannot vertically pass through a block above him
27451 PUSH AF Store AF
27452 XOR A Set A to zero (Magic Knight) and...
27453 CALL 39224 ...draw Magic Knight (erase old frame and draw new frame)
27456 POP AF Restore AF
27457 JR NZ,27468 If Magic Knight's jump was impeded by a block above him then jump to 27468
27459 CALL 29763 Run checks and updates (Magic Knight's current room and room-specific routines)
27462 LD HL,(41857) Load HL with current position in Magic Knight's y-velocities sequence table at 41857
27465 INC HL Advance to next y-velocity in the sequence
27466 JR 27381 Loop back to 27381
27468 CALL 34821 Update Magic Knight's current frame based on x-coordinate
27471 LD (65528),A Store frame number at 65528
27474 CALL 27490 Handle Magic Knight's fall, preserving x-velocity
27477 JP 27254 Loop back to start of keyboard check routine
27480 XOR A Set Magic Knight's x-velocity to zero...
27481 LD (25391),A ...
27484 LD (27405),A Prepare to set Magic Knight's x-velocity to zero
27487 JP 27439 Jump back to 27439
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