Drawing the screen: BOXS

       Name: BOXS                                                    [Show more]
       Type: Subroutine
   Category: Drawing the screen
    Summary: Draw a horizontal line across the screen at pixel y-coordinate X
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * TTX66K calls BOXS


 Arguments:

   X                    The pixel y-coordinate for the line


.BOXS

 STX Y1                 ; Set Y1 = X

 LDX #0                 ; Set X1 = 0
 STX X1

 DEX                    ; Set X2 = 255
 STX X2

 JMP HLOIN              ; Call HLOIN to draw a horizontal line from (X1, Y1) to
                        ; (X2, Y1), so that's from (0, X) to (255, X), and
                        ; return from the subroutine using a tail call