Drawing dividing lines

I find it really hard to draw lines to split the canvas image into multiple parts. Say, I want to draw an image and I want to split it perfectly in the center with a white line, actually I can’t find any feature to help with that. Once I draw a line it is very hard to reposition it and I don’t exactly know where to reposition it as I don’t know the image dimensions.

I was creating a pong clone and I had to split the image with a white line in the center for separating halves. I would like it if there was a feature to easily do this based on percentage.

I think this feature will also be helpful for comic book artist that use krita. You know, splitting page into portions with black lines based on the squares or rectangle specified.

Thank You for reading.