Drawing the screen: cleargrap

       Name: cleargrap                                               [Show more]
       Type: Subroutine
   Category: Drawing the screen
    Summary: Clear screen memory for the top part of the graphics screen mode
             (the space view), drawing blue borders along the sides as we do so
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * clss calls cleargrap
             * TTX66K calls cleargrap


.cleargrap

 LDY #16                ; Set a counter in Y to clear the 17 character rows of
                        ; the space view

.cleargl

 JSR clearrow           ; Clear character row Y in screen memory, drawing blue
                        ; borders along the left and right edges as we do so

 DEY                    ; Decrement the row counter

 BPL cleargl            ; Loop back until we have cleared all 17 character rows

 INY                    ; Y is decremented to 255 by the loop, so this sets Y to
                        ; zero

 STY XC                 ; Move the text cursor to column 0 on row 0
 STY YC

 RTS                    ; Return from the subroutine