Skip to navigation

⌂ ∞ Elite on the BBC Micro and NES

Drawing pixels: CPIX2

[Elite-A, Parasite]

       Name: CPIX2                                                   [Show more]
       Type: Subroutine
   Category: Drawing pixels
    Summary: Draw a single-height dash on the dashboard by sending a draw_blob
             command to the I/O processor

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * CPIX4 calls CPIX2
             * DOT calls CPIX2




 Arguments:

   X1                   The screen pixel x-coordinate of the dash

   Y1                   The screen pixel y-coordinate of the dash

   COL                  The colour of the dash as a mode 5 character row byte



.CPIX2

 LDA #&90               \ Send command &90 to the I/O processor:
 JSR tube_write         \
                        \   draw_blob(x, y, colour)
                        \
                        \ which will draw a dash of the specified colour and
                        \ position on the dashboard

 LDA X1                 \ Send the first parameter to the I/O processor:
 JSR tube_write         \
                        \   * x = X1

 LDA Y1                 \ Send the second parameter to the I/O processor:
 JSR tube_write         \
                        \   * y = Y1

 LDA COL                \ Send the third parameter to the I/O processor:
 JMP tube_write         \
                        \   * colour = COL
                        \
                        \ and return from the subroutine using a tail call