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⌂ ∞ ▽ Elite on the BBC Micro and NES

Drawing lines: HLOIN2

[6502 Second Processor version, I/O processor]

       Name: HLOIN2                                                  [Show more]
       Type: Subroutine
   Category: Drawing lines
    Summary: Draw a horizontal line in a specific colour

    Context: See this subroutine in context in the source code
 Variations: See code variations for this subroutine in the different versions
 References: This subroutine is called as follows:
             * LOIN (Part 1 of 7) calls HLOIN2




 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

   COL                  The line colour



.HLOIN2

 LDX X1                 \ Set X = X1

 STY Y2                 \ Set Y2 = Y, the offset within the line buffer of the

 INY                    \ Set Q = Y + 1, so the call to HLOIN3 only draws one
 STY Q                  \ line

 LDA COL                \ Set A to the line colour

 JMP HLOIN3             \ Jump to HLOIN3 to draw a line from (X, Y1) to (X2, Y1)
                        \ in the colour given in A