Routines
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58361: Controls: Left
Used by the routine at Controls_CheckRight.
Did the player press left?
Controls_CheckLeft 58361 CP 2 Jump to Controls_CheckDown if the player didn't press left (2).
58363 JR NZ,Controls_CheckDown
Left movement checks for boundaries and the home box.
MoveLeft_Checks 58365 LD A,(55341) A=*DestinationCursor_X_Position.
Can the player move left?
58368 CP 5 If *DestinationCursor_X_Position is at or beyond the left-most boundary jump to *Handler_CursorMovement.
58370 JP M,Handler_CursorMovement
Is the player about to enter the home box?
This is position 6/ 2:
cursor-06-02
58373 CP 6 If *DestinationCursor_X_Position is not 6 (which confirms the player can't be beside the home box), jump to MoveLeft.
58375 JR NZ,MoveLeft
If the horizontal co-ordinate is 6 and the vertical co-ordinate is 2 then the player IS beside the home box.
58377 LD A,(55340) Now compare *DestinationCursor_Y_Position with 2.
58380 CP 2
58382 LD A,(55341) Reload *DestinationCursor_X_Position into A.
58385 JR NZ,MoveLeft If *DestinationCursor_Y_Position is not 2 (which confirms the player can't be beside the home box), jump to MoveLeft.
Else the player is entering the home box, so the treatment of the cursor isn't quite so simple.
58387 SUB 4 Move *DestinationCursor_X_Position to 4 character blocks to the left.
58389 LD (55341),A
58392 DEC (HL) Update the tile ID the player will land on.
58393 CALL Remove_PlayerCursor Call Remove_PlayerCursor.
Animate the cursor entering the home box.
58396 LD HL,55343 HL=CurrentCursor_X_Position.
Each valid direction moves the cursor one-cursor-width character blocks and rather than simply jump the whole way, the game auto-moves one character block at a time until the cursor reaches it's destination.
I've called these "frames" here, but it's the same cursor just moving between positions, there are no differently stored frames.
58399 LD B,4 Set a counter in B for 4 animation "frames".
58401 CP 2 Jump to MoveLeft_Checks if A is equal to 2.
58403 JR Z,MoveLeft_Checks
AnimateMoveLeft_Loop 58405 PUSH BC Stash the frame counter and horizontal position on the stack.
58406 PUSH HL
To demonstrate the four "frames" of movement:
6 5 4 3
cursor-06-02 cursor-05-02 cursor-04-02 cursor-03-02
If the code only called Draw_Cursor then the above is what would actually display! Instead the default attributes are written to the home box very quickly, and then the code forces a HALT to wait for the next frame to avoid any flicker.
So this is what is actually displayed:
6 5 4 3
cursor-good-06-02 cursor-good-05-02 cursor-good-04-02 cursor-good-03-02
And then position 2 is handled below by setting *PlayerCursor_Flag to 0.
58407 CALL Draw_Cursor Call Draw_Cursor.
58410 CALL Home_DefaultAttributes Call Home_DefaultAttributes.
58413 CALL Sound_Cursor Call Sound_Cursor.
Wait for the next frame.
58416 HALT Halt operation (suspend CPU until the next interrupt).
58417 CALL Remove_PlayerCursorAttributes Call Remove_PlayerCursorAttributes.
58420 POP HL Restore the horizontal position and frame counter from the stack.
58421 POP BC
58422 DEC (HL) Move the cursor position left by one character block.
58423 DJNZ AnimateMoveLeft_Loop Decrease the frame counter by one and loop back to AnimateMoveLeft_Loop until all 4 frames have played.
Mark that the cursor is now inside the home box.
58425 LD A,0 Write 0 to *PlayerCursor_Flag.
58427 LD (55349),A
Update the stored cursor positions.
58430 LD A,(55340) Write *DestinationCursor_Y_Position to *StorageCursor_Y_Position.
58433 LD (55344),A
58436 LD A,(55341) Write *DestinationCursor_X_Position to *StorageCursor_X_Position.
58439 LD (55345),A
58442 RET Return.
Normal left movement.
MoveLeft 58443 SUB 4 Move 4 character blocks left.
58445 LD (55341),A Update *DestinationCursor_X_Position.
Update the tile ID the player has now landed on.
58448 DEC (HL) Decrease *HL by one.
58449 JP Handler_CursorMovement Jump to Handler_CursorMovement.
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