Thanks all for your comments.
There are three kinds of lines I am interested in.
Horizontal lines with the level value marked on the left (this feature already was there. That is the most drawing feature I used so far, thanks to the auto-focus feature in the new platform, it saved a lot of time to locate the tip of a candle)
The second type is similar to the horizontal line, but only extend it to the right of the chart, not the left. ( This should be quite easy to be implemented).
The third type is a horizontal point to point line. It is ok to be out of shape after changing to the low time fame. That does not mean it is not horizontal any more in low time frame. I meant it is ok it does not reach the point you draw in high time frame. You can always extend it again in low time frame. But still need to keep it horizontal when extending it.
All of these should not be difficult.
I can understand why the trend line you draw in high time frame will be out of shape in low time frame. It is reasonable, even in MT4 it will be out of shape.
Currently I found some workaround (not perfect). I used the gann fan feature, and keep the angle is 0. One problem of this is the line is not long enough(no visible) when you change to low time frame. It is not ideal, but that is what we got so far.