Enable Infinite Scrolling, setting Diagram.scrollMode

      myDiagram.scrollMode = checked ? go.Diagram.InfiniteScroll : go.Diagram.DocumentScroll;
    

Enable Diagram.positionComputation function

      function positionfunc(diagram, pos) {
        var size = diagram.grid.gridCellSize;
        return new go.Point(
          Math.round(pos.x / size.width) * size.width,
          Math.round(pos.y / size.height) * size.height);
      }
    

Enable Diagram.scaleComputation function

      function scalefunc(diagram, scale) {
        var oldscale = diagram.scale;
        if (scale > oldscale) {
          return oldscale + 0.25;
        } else if (scale < oldscale) {
          return oldscale - 0.25;
        }
        return oldscale;
      }
    

This demonstrates new scrolling and scaling options available in GoJS 1.5.