At this moment, the Scheduler doesn't support loading additional resources during scrolling. All resources need to be loaded in advance using .resources array.
1. The row headers are rendered progressively so loading a large number of resources scales relatively well.
2. If your resources are organized in a tree hierarchy you can load the node children on demand - http://doc.daypilot.org/scheduler/dynamic-resource-tree-loading/
The events can be loaded on-demand (during scrolling).
See the following doc page for more details:
See also the following tutorial (it includes sample PHP project):