Routines
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E39C: Controls: Right
Did the player press right?
Controls_CheckRight E39C CP $01 Jump to Controls_CheckLeft if the player didn't press right (01).
E39E JR NZ,Controls_CheckLeft
Right movement checks for boundaries and the home box.
MoveRight_Checks E3A0 LD A,($D82D) A=*DestinationCursor_X_Position.
Can the player move right?
E3A3 CP $0F If *DestinationCursor_X_Position is at or beyond the right-most boundary jump to *Handler_CursorMovement.
E3A5 JP P,Handler_CursorMovement
Is the player inside the home box?
The game restricts this (i.e. this image would never happen), but to demonstrate - this is position 02/ 02:
cursor-02-02
E3A8 CP $02 If *DestinationCursor_X_Position is not 02 (which confirms the player can't be inside the home box), jump to MoveRight.
E3AA JR NZ,MoveRight
If both the horizontal and the vertical co-ordinates are 02 then the player IS inside the home box.
E3AC LD A,($D82C) Now compare *DestinationCursor_Y_Position with 02.
E3AF CP $02
E3B1 LD A,($D82D) Reload *DestinationCursor_X_Position into A.
E3B4 JR NZ,MoveRight If *DestinationCursor_Y_Position is not 02 (which confirms the player can't be inside the home box), jump to MoveRight.
Else the player is inside the home box, so the treatment of the cursor isn't quite so simple.
E3B6 ADD A,$04 Move *DestinationCursor_X_Position to 04 character blocks to the right.
E3B8 LD ($D82D),A
E3BB INC (HL) Update the tile ID the player will land on.
E3BC LD A,$00 Write 00 to *PlayerCursor_Flag, the cursor is still inside the home box and so isn't drawn to the screen buffer just yet.
E3BE LD ($D835),A
The player is leaving the home box, so reset the colour of the arrow.
E3C1 LD A,$2F A=INK: WHITE, PAPER: CYAN .
E3C3 CALL ColouriseHome Call ColouriseHome.
Animate the cursor leaving the home box.
E3C6 LD HL,$D82F HL=CurrentCursor_X_Position.
E3C9 INC (HL) Move the cursor position right by one character block.
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.
E3CA LD B,$03 Set a counter in B for 03 animation "frames".
AnimateMoveRight_Loop E3CC PUSH BC Stash the frame counter and horizontal position on the stack.
E3CD PUSH HL
To demonstrate the three "frames" of movement:
03 04 05
cursor-03-02 cursor-04-02 cursor-05-02
If the code only called Draw_Cursor then the above is what would actually display! Instead the default attributes are written to the home box very quickly, and then the code forces a HALT to wait for the next frame to avoid any flicker.
So this is what is actually displayed:
03 04 05
cursor-good-03-02 cursor-good-04-02 cursor-good-05-02
And then position 06 is just the cursor being printed normally (hence only 03 "frames" are needed here).
E3CE CALL Draw_Cursor Call Draw_Cursor.
E3D1 CALL Home_DefaultAttributes Call Home_DefaultAttributes.
E3D4 CALL Sound_Cursor Call Sound_Cursor.
Wait for the next frame.
E3D7 HALT Halt operation (suspend CPU until the next interrupt).
E3D8 CALL Remove_PlayerCursorAttributes Call Remove_PlayerCursorAttributes.
E3DB POP HL Restore the horizontal position and frame counter from the stack.
E3DC POP BC
E3DD INC (HL) Move the cursor position right by one character block.
E3DE DJNZ AnimateMoveRight_Loop Decrease the frame counter by one and loop back to AnimateMoveRight_Loop until all 03 frames have played.
Display the cursor in its final position.
E3E0 CALL Display_PlayerCursor Call Display_PlayerCursor.
Update the stored cursor positions.
E3E3 LD A,($D82C) Write *DestinationCursor_Y_Position to *StorageCursor_Y_Position.
E3E6 LD ($D830),A
E3E9 LD A,($D82D) Write *DestinationCursor_X_Position to *StorageCursor_X_Position.
E3EC LD ($D831),A
E3EF RET Return.
Normal right movement.
MoveRight E3F0 ADD A,$04 Move 04 character blocks right.
E3F2 LD ($D82D),A Update *DestinationCursor_X_Position.
Update the tile ID the player has now landed on.
E3F5 INC (HL) Increment *HL by one.
E3F6 JP Handler_CursorMovement Jump to Handler_CursorMovement.
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