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⌂ ∞ Elite on the BBC Micro and NES

Drawing lines: HLOIN

[Elite-A, Parasite]

       Name: HLOIN                                                   [Show more]
       Type: Subroutine
   Category: Drawing lines
    Summary: Draw a horizontal line by sending a draw_hline command to the I/O
             processor

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * NLIN2 calls HLOIN
             * SUN (Part 3 of 4) calls HLOIN
             * TT15 calls HLOIN
             * TTX66 calls HLOIN




 Arguments:

   X1                   The screen x-coordinate of the start of the line

   X2                   The screen x-coordinate of the end of the line

   Y1                   The screen y-coordinate of the line



.HLOIN

 LDA #&81               \ Send command &81 to the I/O processor:
 JSR tube_write         \
                        \   draw_hline(x1, y1, x2)
                        \
                        \ which will draw a horizontal line from (x1, y1) to
                        \ (x2, y1)

 LDA X1                 \ Send the first parameter to the I/O processor:
 JSR tube_write         \
                        \   * x1 = X1

 LDA Y1                 \ Send the second parameter to the I/O processor:
 JSR tube_write         \
                        \   * y1 = Y1

 LDA X2                 \ Send the first parameter to the I/O processor:
 JMP tube_write         \
                        \   * x2 = X2
                        \
                        \ and return from the subroutine using a tail call