Routines
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56293: Move Tile Left
Used by the routines at 61025 and 62526.
MoveTile_Left 56293 LD A,(59229) Take *Tile_Horizontal_Position and decrease it by one, which adjusts the value for the tile width. Write this value back to *Tile_Horizontal_Coordinate.
56296 DEC A
56297 LD (59231),A
Set the total of how many spaces the tile will be moving.
56300 LD A,(59233) B=*Tile_SpacesToMove.
56303 LD B,A
This is the tile loop, each space moved will decrease this counter by one.
MoveTile_Left_Loop 56304 PUSH BC Stash the number of spaces left to move on the stack.
56305 LD A,(59230) Take *Tile_Vertical_Position and subtract 1 which adjusts the value for the tile height. Write this value back to *Tile_Vertical_Coordinate.
56308 DEC A
56309 LD (59232),A
Start moving the tile a single space.
56312 LD B,4 Set a counter in B for the height of the tile in bytes (4 rows).
MoveTile_Left_RowLoop 56314 PUSH BC Stash the row counter (tile height) on the stack.
Get the screen buffer address from the co-ordinates.
56315 LD A,(59231) B=*Tile_Horizontal_Coordinate.
56318 LD B,A
56319 LD A,(59232) C=*Tile_Vertical_Coordinate.
56322 LD C,A
56323 CALL Calculate_ScreenBlockAddress Call Calculate_ScreenBlockAddress.
56326 LD A,8 Set the number of bytes in a character block to A.
56328 LD BC,4 Set a counter in B for the number of bytes in a row (4), and set C to 0 which is used for erasing the left-over tile pixels.
56331 PUSH HL HL=screen buffer address of the tile.
56332 POP DE DE=screen buffer address of the tile (using the stack) - 1.
56333 DEC DE
56334 PUSH HL Stash the current screen buffer address of the tile on the stack.
Start moving the current row.
MoveTile_Left_ColumnLoop 56335 PUSH HL Stash the current screen buffer address of the tile on the stack.
56336 LDIR Move 0004 screen data bytes from left to right.
This leaves the last byte unprocessed - which should be blank. So, let's erase it.
56338 DEC HL Erase the right-most byte (C contains 0).
56339 LD (HL),C
56340 POP HL Restore the current screen buffer address from the stack.
56341 INC H Move down one row.
Update the screen buffer address for the next loop iteration.
56342 PUSH HL HL=screen buffer address of the tile.
56343 POP DE DE=screen buffer address of the tile (using the stack) - 1.
56344 DEC DE
56345 LD BC,4 Restore BC back to 0004.
56348 DEC A Decrease the column/ byte counter by one.
56349 JP NZ,MoveTile_Left_ColumnLoop Jump to MoveTile_Left_ColumnLoop until all four bytes in this row have been moved.
Now onto the attribute buffer bytes.
Convert the screen buffer location into a corresponding attribute buffer address.
56352 POP HL Restore the current screen buffer address from the stack.
56353 CALL Calculate_AttributeAddress Call Calculate_AttributeAddress.
56356 PUSH DE HL=attribute buffer address of the tile (using the stack).
56357 POP HL
56358 DEC DE DE=attribute buffer address of the tile - 1.
56359 LD BC,5 Move 0005 attribute bytes from left to right.
56362 LDIR
This leaves the last attribute space unprocessed - which should be blank. So, let's erase it.
56364 LD A,71 A=INK: WHITE, PAPER: BLACK (BRIGHT) .
56366 DEC DE Erase the right-most attribute block.
56367 LD (DE),A
Move to the next attribute row.
56368 LD HL,59231 Increment *Tile_Horizontal_Coordinate by one.
56371 INC (HL)
56372 POP BC Restore the attribute row counter from the stack.
56373 DJNZ MoveTile_Left_RowLoop Decrease the attribute row counter by one and loop back to MoveTile_Left_RowLoop until the whole row has been processed.
The tile has successfully moved one space!
56375 POP BC Using the number of spaces left to move (from the stack) call Sound_TileMovement.
56376 PUSH BC
56377 CALL Sound_TileMovement
56380 LD A,(59229) Take *Tile_Horizontal_Position and decrease it by one, which adjusts the value for the tile width. Write it back to *Tile_Horizontal_Coordinate.
56383 DEC A
56384 LD (59231),A
56387 LD HL,59230 Decrease *Tile_Vertical_Position by one.
56390 DEC (HL)
56391 POP BC Restore the number of spaces left to move from the stack.
56392 DJNZ MoveTile_Left_Loop Decrease the number of spaces counter by one and loop back to MoveTile_Left_Loop until the tile is in the destination space.
56394 RET Return.
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