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⌂ ∞ Elite on the BBC Micro and NES

Drawing lines: CLIP_b1

[NES version, Bank 7]

       Name: CLIP_b1                                                 [Show more]
       Type: Subroutine
   Category: Drawing lines
    Summary: Call the CLIP routine in ROM bank 1, drawing the clipped line if
             it fits on-screen
  Deep dive: Splitting NES Elite across multiple ROM banks

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * DrawScrollFrame calls CLIP_b1




.CLIP_b1

 LDA currentBank        ; Fetch the number of the ROM bank that is currently
 PHA                    ; paged into memory at $8000 and store it on the stack

 LDA #1                 ; Page ROM bank 1 into memory at $8000
 JSR SetBank

 JSR CLIP               ; Call CLIP, now that it is paged into memory

 BCS P%+5               ; If the C flag is set then the clipped line does not
                        ; fit on-screen, so skip the next instruction

 JSR LOIN               ; The clipped line fits on-screen, so draw it

 JMP ResetBank          ; Fetch the previous ROM bank number from the stack and
                        ; page that bank back into memory at $8000, returning
                        ; from the subroutine using a tail call