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⌂ ∞ ▽ Elite on the 6502

Drawing the screen: DrawRowOfTiles

[NES version, Bank 3]

       Name: DrawRowOfTiles                                          [Show more]
       Type: Subroutine
   Category: Drawing the screen
    Summary: Draw a row of tiles into the nametable buffer

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * DrawImageFrame calls DrawRowOfTiles
             * DrawSmallBox calls DrawRowOfTiles




 This routine effectively draws K tiles at SC(1 0) and SC2(1 0), but omitting
 the first tile.



 Arguments:

   A                    The pattern number to use for the row of tiles

   K                    The number of tiles to draw, minus 1 (so we draw K - 1
                        tiles)

   SC(1 0)              The address in nametable buffer 0 for the start of the
                        row, less 1 (we draw from SC(1 0) + 1 onwards)

   SC2(1 0)             The address in nametable buffer 1 for the start of the
                        row, less 1 (we draw from SC2(1 0) + 1 onwards)



.DrawRowOfTiles

 LDY #1                 ; We start drawing from SC(1 0) + 1, so set an index
                        ; counter in Y

.drow1

 STA (SC),Y             ; Draw the pattern in A into the Y-th nametable entry
 STA (SC2),Y            ; in both the nametable buffers

 INY                    ; Increment the index counter

 CPY K                  ; Loop back until we have drawn K - 1 tiles
 BNE drow1

 RTS                    ; Return from the subroutine