randomly fill a jit.matrix

hi, I need a solution for randomly filling a plane of a jit.matrix. every bang must shot 2 value, an x and an y position. the problem for me is obtain a valid combination for every bang, and avoid the repetition. I know how to obtain a random value without repetition, but I can't obtain an efficient random xy cordinates because, for example I need the 768 value 4080 times (768 0, 768 1, 768 1 etc etc). here my patch