Drawing lines: HLOIN2

       Name: HLOIN2                                                  [Show more]
       Type: Subroutine
   Category: Drawing lines
    Summary: Remove a line from the sun line heap and draw it on-screen
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * SUN (Part 2 of 4) calls HLOIN2
             * SUN (Part 4 of 4) calls HLOIN2


 Specifically, this does the following:

   * Set X1 and X2 to the x-coordinates of the ends of the horizontal line with
     centre YY(1 0) and length A to the left and right

   * Set the Y-th byte of the LSO block to 0 (i.e. remove this line from the
     sun line heap)

   * Draw a horizontal line from (X1, Y) to (X2, Y)


 Arguments:

   YY(1 0)              The x-coordinate of the centre point of the line

   A                    The half-width of the line, i.e. the contents of the
                        Y-th byte of the sun line heap

   Y                    The number of the entry in the sun line heap (which is
                        also the y-coordinate of the line)


 Returns:

   Y                    Y is preserved


.HLOIN2

 JSR EDGES              \ Call EDGES to calculate X1 and X2 for the horizontal
                        \ line centred on YY(1 0) and with half-width A

 STY Y1                 \ Set Y1 = Y

 LDA #0                 \ Set the Y-th byte of the LSO block to 0
 STA LSO,Y

                        \ Fall through into HLOIN to draw a horizontal line from
                        \ (X1, Y) to (X2, Y)