L E Dickson's (1920) method for generating Pythagorean triples
Use the slider to change the value of r. The construction will generate Pythagorean triples depending on the values s and t. Note that r=2*radius of the incircle
L.E. Dickson. History of the theory of numbers, vol. 2: Diophantine analysis. Carnegie Institution of Washington, Publication No. 256, 2:169, 1920.