javascript - How do I animate a protovis streamgraph? -

i'm having trouble figuring out how animate protovis streamgraph. think best way pass array of i, j indexes .layers() , have .x() , .y() functions actual updating values. there simpler way?

couldn't update data before every render? assuming data has changed, i'm not sure see benefit doing otherwise, think whole vis need re-render.

function getdata(offset) {    // get/create data here, maybe seeded offset }  var offset = 0;  // ... define scales , stuff  var vis = new pv.panel()     .width(w)     .height(h);  vis.add(pv.layout.stack)      // wrap in function re-evaluate on render     .layers(function() getdata(offset))     .offset("wiggle")     .x(x.by(pv.index))     .y(y) .layer.add(pv.area);  // use setinterval animate setinterval(function() {      offset++; // still working on offset idea     vis.render();  }, 20); 

this seems work, though depends kind of animation you're looking create - there may more efficient approaches kinds of animation.