foreshortening, for shortening

Foreshortening or foreshortening ( one word ) means a method of distorting a drawing or image to give the illusion of three dimensions--
The foreshortening gives the painting an odd look; maybe you could try a different angle.
See how the foreshortening makes the figure appear to exist in real space.

For shortening or for shortening ( two words ) means with the purpose or object of, or in consideration of ( for ) making something smaller in length ( shortening )--
How much did he charge for shortening the dress?
We still owe the tailor for shortening those pants.

For shortening ( two words ) may also mean in exchange ( for ) vegetable fat used in cooking or baking ( shortening )--
Can I substitute butter for shortening in this recipe?
You can use vegetable oil for shortening, if we're out of butter.

Now that you know that, you can say--
"The foreshortening will look more realistic if you use a ruler for shortening the back legs of the table."

Note--"foreshortened" means distorted to give the illusion of three dimensions--
The drawing is foreshortened in the front; part of the figure seems to be close to the viewer.
Not to be confused with "for shortened", meaning suiting the purpose of  ( for ) [ something ] made smaller in length ( shortened )--
This is just the weather for shortened school days.