Routines
Prev: BB45 Up: Map Next: BB7C
BB5C: Clear Play Area
Used by the routines at GameComplete, ShowAmulet, HandlerPoems, GameOver_1UP_Messaging, EnterRoomBelow, InitialiseGame, SwitchPlayer and HandlerGameMenu.
Clears the top third of the screen, but only from below the banner. The banner is left untouched.
Before After
clear-before clear-after
ClearPlayArea BB5C LD HL,$4040 HL=4040(screen buffer).
Here D contains the value to be written (00) and E holds the number of rows of pixels to act on (the full height of a character block).
BB5F LD DE,$0008 DE=0008.
B holds the number of columns (i.e. 20 == full width of the screen), and C is a counter for how many rows to clear (i.e. the top third would usually be 08 rows, but the banner takes up two - hence this initialises to 06).
BB62 LD BC,$2006 BC=2006.
ClearPlayArea_ClearLine BB65 PUSH BC Stash BC and HL on the stack.
BB66 PUSH HL
ClearPlayArea_ClearLine_Start BB67 PUSH BC Stash BC on the stack.
ClearPlayArea_ClearLine_Loop BB68 LD (HL),D Write 00 (D) to the screen (HL).
BB69 INC L Move "right" onto the next column.
BB6A DJNZ ClearPlayArea_ClearLine_Loop Decrease the width counter by one and loop back to ClearPlayArea_ClearLine_Loop until counter is zero.
Resets the width counter ready for the next loop.
BB6C POP BC Restore BC from the stack.
BB6D DEC C Decrease the number of rows counter by one.
BB6E JR NZ,ClearPlayArea_ClearLine_Start Jump back to ClearPlayArea_ClearLine_Start unless C is zero.
Resets the screen buffer to where the clearing started for this loop, then moves down one character block.
BB70 POP HL Restore HL from the stack.
BB71 INC H Increments H by one.
BB72 POP BC Restore BC from the stack.
BB73 DEC E Decrease the pixel row counter by one.
BB74 JR NZ,ClearPlayArea_ClearLine Jump back to ClearPlayArea_ClearLine unless E is zero.
Clears the other two thirds of the screen, so now the screen only contains the banner.
BB76 LD HL,$4800 HL=4800(screen buffer).
BB79 JP ResetScreen_FromAddress Jump to ResetScreen_FromAddress.
Prev: BB45 Up: Map Next: BB7C