docs: function enterFrame() {
                  if (dur > 0) {
  					if (isFinite(Crafty.viewport._zoom)) zoom = Crafty.viewport._zoom;
                      var old = {
                          width: act.width * zoom,
                          height: act.height * zoom
                      };
                      zoom += zoom_tick;
                      Crafty.viewport._zoom = zoom;
                      var new_s = {
                          width: act.width * zoom,
                          height: act.height * zoom
                      },
                      diff = {
                          width: new_s.width - old.width,
                          height: new_s.height - old.height
                      };
                      Crafty.stage.inner.style[prop] = 'scale(' + zoom + ',' + zoom + ')';
                      if (Crafty.canvas._canvas) {
  						var czoom = zoom / (zoom - zoom_tick);
  						Crafty.canvas.context.scale(czoom, czoom);
                          Crafty.DrawManager.drawAll();
                      }
                      Crafty.viewport.x -= diff.width * prct.width;
                      Crafty.viewport.y -= diff.height * prct.height;
                      dur--;
                  }
              }