The visitor here was greeted both in the entrance hall and at the start of the exhibition by Punchinello, the historic animator of the stage. David Hockney’s giant figures, attired in emerald green from high hat to pointed toe, ushered the viewer into Martin Friedman’s carefully organized display of Hockney’s stage designs. The 270 items on show were an unusually lively mixture of works and ideas for works, including drawings, paintings, scale models, and entrancing objects like the childrens’ bricks from which Hockney conceived the props for the triple bill of Erik Satie’s Parade, Francis