It is easy to make a pattern on your fabric. If you only need 4 half sq triangles say 2 1/2 in size. Cut a rectangle of two fabrics right sides togather that is 3 in by 6 inchs. Draw a line at the 3 in middle then draw lines corner to corner from that line. \l/ . Sew 1/4 in from each side of angled lines. Cut on all drawn lines then square up to 2 1/2 inchs. They will come out perfect every time. For each size larger add 2 inchs.
I have tried many different methods including buying already marked patterns but that is a waste of money when it is so simple just to draw on the fabric.
There is a ruler that makes squaring up the triangles easy too.
Quilt in a Day has it. You just lay the line on the triangle before opening and cut two cuts and it is squared up. Fast easy and perfect every time.