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Routines |
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Clears the pixels of the play area, which is the left-hand 18 bytes of each of the C0 rows of the screen buffer. The attributes are left alone.
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| ClearPlayArea | 8093 | LD HL,$4000 | HL=4000 (the start of the screen buffer). | |||||
| 8096 | LD BC,$18C0 | B=18 (the number of bytes to clear in each row) and C=C0 (the number of rows). | ||||||
| 8099 | XOR A | A=00 (the value to write). | ||||||
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This entry point is used by the routines at DrawRoomFrame and DrawSidePanelAttrs.
Each pass of this loop clears one row.
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| ClearPlayArea_Row | 809A | PUSH BC | Stash the counters on the stack. | |||||
| 809B | PUSH HL | Stash the row address on the stack. | ||||||
| 809C | LD DE,$0020 | DE=0020 (the size of a row). | ||||||
| ClearPlayArea_Byte | 809F | LD (HL),A | Write A to *HL. | |||||
| 80A0 | INC HL | Move HL on to the next byte. | ||||||
| 80A1 | DJNZ ClearPlayArea_Byte | Decrease the byte counter by one and loop back to ClearPlayArea_Byte until the whole row has been cleared. | ||||||
| 80A3 | POP HL | Restore the row address from the stack. | ||||||
| 80A4 | ADD HL,DE | Move HL on to the next row. | ||||||
| 80A5 | POP BC | Restore the counters from the stack. | ||||||
| 80A6 | DEC C | Decrease the row counter by one and loop back to ClearPlayArea_Row until all C0 rows have been cleared. | ||||||
| 80A7 | JR NZ,ClearPlayArea_Row | |||||||
| 80A9 | RET | Return. | ||||||
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