Lines or ruler snapping to grid.

Hey, is there a feature to make lines snap to the grid in order to work very precisely? Or is it possible to snap the ruler to the  grid? So far I have only been able to manually place the ruler on the grid, which results in lines, that don't exactly meet, unfortunately. I know that the perspective grid allows to draw these straight lines but I would love to see that with the drawing aid or the two-dimensional grid.