First of all, I would like to know if there is "guide" functionality in Paint.net.
It is a vertical or horizontal line that elements can snap to. This line can be positioned anywhere within the drawing and function as guide for placement.
Second is, would be great if this guide can be "grabbed" from the side and top ruler pane. Meaning move the mouse on top of the ruler pane, click and drag the mouse pointer into drawing area. During dragging a visual cue is display in the form of vertical or horizontal line that move with the mouse cursor. Releasing the mouse button cause the vertical or horizontal guide line to be place into the drawing.
Cheers!