LEBANI Sirenje is sitting on a rooftop on Auret Street in Maboneng, Johannesburg. Every few seconds he glances at a picture of the late South African rapper and dancer, Costa Titch - then translates what he sees onto canvas. His brush strokes move in sync with the beat of the AmaPiano house music searing the calm of a Sunday afternoon. The song on the speakers changes - a faster tune now - but Sirenje's rhythmic strokes remain unchanged as he works on the painting. Sirenje, popularly known as Rasta The Artist, is famous for painting portraits of public figures who…