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
 Variations: See code variations for this subroutine in the different versions
 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

 STA Y2                 \ Set Y2 = A

 LDA #YELLOW            \ Send a #SETCOL YELLOW command to the I/O processor to
 JSR DOCOL              \ switch to colour 1, which is yellow

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

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

 JSR LL30               \ Call LL30 to draw a line from (2, A) to (254, A)

 LDA #CYAN              \ Send a #SETCOL CYAN command to the I/O processor to
 JMP DOCOL              \ switch to colour 3, which is cyan or white