Routines
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6B42: Plot interior tiles
This routine expands all of the tile indices in the visible tiles array to the screen buffer. It's only ever used when drawing interior scenes (rooms).
Used by the routines at enter_room, pick_up_item, process_player_input, wake_up, end_of_breakfast, select_room_and_plot, screen_reset, choose_game_window_attributes and action_shovel.
plot_interior_tiles 6B42 LD HL,$F290 Point HL at the screen buffer's start address
6B45 LD DE,$F0F8 Point DE at the visible tiles array
6B48 LD C,$10 Set row counter to 16
For every row
row_loop 6B4A LD B,$18 Set column counter to 24
For every column
column_loop 6B4C PUSH HL Stack screen buffer pointer while we form a tile pointer
6B4D LD A,(DE) Load a tile index
6B4E EXX Bank outer registers
6B4F LD L,A Point HL at interior_tiles[tile index]
6B50 LD H,$00
6B52 ADD HL,HL
6B53 ADD HL,HL
6B54 ADD HL,HL
6B55 LD DE,$9768
6B58 ADD HL,DE
6B59 POP DE Unstack screen buffer pointer
6B5A LD BC,$0818 Simultaneously set B for eight iterations and C for a 24 byte stride
tile_loop 6B5D LD A,(HL) Transfer a byte (a row) of tile across
6B5E LD (DE),A
6B5F LD A,C Advance the screen buffer pointer by the stride
6B60 ADD A,E
6B61 JR NC,plot_interior_tiles_0
6B63 INC D
plot_interior_tiles_0 6B64 LD E,A
6B65 INC L
6B66 DJNZ tile_loop ...loop for each byte of the tile
End of column
6B68 EXX Unbank outer registers
6B69 INC DE Move to next input tile
6B6A INC HL Move to next screen buffer output
6B6B DJNZ column_loop ...loop for each column
End of row
6B6D LD A,$A8 Move to the next screen buffer row (seven rows down)
6B6F ADD A,L
6B70 JR NC,plot_interior_tiles_1
6B72 INC H
plot_interior_tiles_1 6B73 LD L,A
6B74 DEC C ...loop for each row
6B75 JP NZ,row_loop
End
6B78 RET Return
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