function! MouseScrollTouch()
  "mark b is the current cursor position
  "mark a is the previous cursor position
  norm mb
  let currPos= line('.')
  norm `a
  let prevPos= line('.')
  let amt= 1 + abs(currPos - prevPos) / 2
  "norm `bma
  while amt > 0
    if currPos>prevPos
      norm 
    elseif currPos<prevPos
      "norm `bma
      norm 
    endif
    let amt= amt - 1
  endwhile
endfunction

function! MouseScrollClick()
  "mark b is the current cursor position
  "mark a is the previous cursor position
  norm mb
  let currPos= line('.')
  norm `a
  let prevPos= line('.')
  let amt= 1 + abs(currPos - prevPos) / 2
  norm `bma
  while amt > 0
    if currPos>prevPos
      norm 
    elseif currPos<prevPos
      "norm `bma
      norm 
    endif
    let amt= amt - 1
  endwhile
endfunction

map <LeftDrag> ma<LeftMouse>:call MouseScrollTouch()<cr>