In this version, I added the ability to fix an angle.
Now you can fix one or two sides, or one angle by repeatedly clicking on the fix part's button.
Next I would like to make it so that you can fix one or two sides and an angle (Side Side Angle case) but I think I will do any further development in Flash so I can make better use of functions. Coding a project this complex in Scratch is just getting too tedius.
Sometimes when you move a vertex, the program will only approximately fix an angle or a side. It is better if you move things slowly. I am hoping to get better results in Flash.