Drag window

Okay so I am making my custom UI.
but I am stuck on the part where people can drag the window, since it's a Borderless form.
I have right now an onMousedown even that checks if the Y of the mouse is smaller than 20, if it is, we set drag to true, and we get the or_x and or_y (origin) by substracting the window's Left to the X of the mosue and the window's Top to the mouse's Y.
Then i have an onMouseMove event that checks if drag is true, and if it is, then
Form1.Top:=Y+or_y;
Form1.Left:=X+or_x;

Now this kind of works, but the window flickers like crazy! Got a clue what i should do?

Try placing timer in your program to control moving of the window.....maybe that will help.
What i want to say if in every predefined amount of time window is moved for the same amount of pixels, it wont flicker......