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


 This draws a line from (0, A) to (255, A), which runs across the whole screen.


 Arguments:

   A                    The pixel row on which to draw the horizontal line


.NLIN2

 STA Y1                 ; Set Y1 = A

 LDA #BLUE              ; Switch to colour blue
 STA COL

 LDX #0                 ; Set X1 = 0, so (X1, Y1) = (0, A)
 STX X1

 DEX                    ; Set X2 = 255, so (X2, Y2) = (255, A)
 STX X2

 JMP HLOIN              ; Call HLOIN to draw a line from (0, A) to (255, A),
                        ; returning from the subroutine using a tail call