Drawing lines: NLIN2

       Name: NLIN2                                                   [Show more]
       Type: Subroutine
   Category: Drawing lines
    Summary: Draw a screen-wide horizontal line at the pixel row in A
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * NLIN4 calls NLIN2
             * TT22 calls NLIN2


 This draws a line from (2, A) to (254, A), which is almost screen-wide and
 fits in nicely between the border boxes without clashing with it.


 Arguments:

   A                    The pixel row on which to draw the horizontal line


.NLIN2

 STA Y1                 \ Set Y1 = A

 LDX #2                 \ Set X1 = 2, so (X1, Y1) = (2, A)
 STX X1

 LDX #254               \ Set X2 = 254, so (X2, Y2) = (254, A)
 STX X2

 BNE HLOIN              \ Call HLOIN to draw a horizontal line from (2, A) to
                        \ (254, A) and return from the subroutine (this BNE is
                        \ effectively a JMP as A will never be zero)