sokoban.love/0036-adjust_scrollbar

adjust_scrollbar = function(state, y)
	local s = (y-state.top) / (state.bottom-state.top)
	local screen_line = s*state.screen_line_count
	local line = 1
	for i=1,#state.lines do
		if state.line_cache[i].start_screen_line_index > screen_line then
			break
		end
		line = i
	end
	state.screen_top1 = {line=line, pos=1}
	state.cursor1 = {line=line, pos=1}
end