i have a form, which you can pretend is laid out like Windows Explorer:

• panel on the left
• splitter

• client panel

  +------------+#+-----------------------+
  |            |#|                       |
  |            |#|                       |
  |            |#|                       |
  |            |#|                       |
  |  Left      |#|      Client           |
  |            |#|                       |
  |            |#|                       |
  |            |#|                       |
  |            |#|                       |
  |            |#|                       |
  +------------+#+-----------------------+
                ^
                |
                +----splitter
  

The the left and client area panels are each rich with controls.

The problem is that using the splitter is very sluggish. i would expect that a modern 2 GHz computer can re-display the form as fast as a human can push the mouse around. But that's definitely not the case, and it takes about 200-300 ms before the form is fully re-adjusted.

The form has about 100 visual controls on it, no code, or custom controls.

How do i go about tracing who's the cause of the sluggishness?