movePlayerUpOrScrollDown

procedure movePlayerUpOrScrollDown();
// player moving up
begin
  if viewRowStart = mapStart then begin
  // at top of map so don't scroll screen down
  // and move normally
    player.yPos := player.yPos + player.yVel;
    Exit;
  end;

  if player.ty >= VIEW_THRESHOLD_T then begin
    // don't scroll yet, not high enough up the screen
    // move normally
    player.yPos := player.yPos + player.yVel;
    Exit;
  end;

  vic_waitForRaster(IRQ_BLANK_LINE);

  // change scroll reg by y-vel (max 2 per frame)
  Dec(scrollY,abs8(player.yVel.b1));

  if scrollY and 128 then begin
  // is negative so wrap around and do hardscroll
    scrollY := scrollY and 7;

    asm
      .for(var y = SCREEN_HEIGHT - 2; y >= VIEW_ROW_OFFSET; y--) {
        ldx #MAP_WIDTH-1
      !:
        lda SCREEN0_ADDRESS + (y + 0) * SCREEN_WIDTH,x
        sta SCREEN0_ADDRESS + (y + 1) * SCREEN_WIDTH,x
        lda COLOR_ADDRESS + (y + 0) * SCREEN_WIDTH,x
        sta COLOR_ADDRESS + (y + 1) * SCREEN_WIDTH,x
        dex
        bpl !-
      }
    end;

    // move view up in map
    Dec(viewRowStart);
    Dec(viewRowEnd);

    // fill top row with level data
    addressPntr1 := levelRowOffset[viewRowStart];
    addressPntr2 := screenRowOffset[VIEW_ROW_OFFSET];

    asm
      clc
      lda addressPntr2 + 0
      adc #<(COLOR_ADDRESS-SCREEN0_ADDRESS)
      sta addressPntr3 + 0
      lda addressPntr2 + 1
      adc #>(COLOR_ADDRESS-SCREEN0_ADDRESS)
      sta addressPntr3 + 1

      ldy #MAP_WIDTH-1
    !:
      lda (addressPntr1),y
      // store level char for color attrib later
      pha
      sta (addressPntr2),y
      // restore level char for color attrib
      pla
      tax
      lda charAttribs,x
      sta (addressPntr3),y
      dey
      bpl !-
    end;
  end;

end;