Has anyone tried producing a dynamic graph in Excel, using VBA and
graphics (not those supplied by charts, but something more exotic like
opengl/directdraw)

It would be interesting to allow the use to set conditions in Excel,
click a macro button which then 'runs' a graphical model in a window.

That's more something normally reserved for other software, but who
knows, Excel is capable of producing a window with Win32 API code
(though it's clumsy). perhaps someone's ventured further.

I can imagine the best would be a control or dll that contains
everything required to manage the window and do the drawing, including
primitives etc, but which can be controlled via vba.

It may even be plausible to link vba up to some established library
liek SDL or Allegro (though i tend to doubt it). TinyPTC or G2 seem
like other possibilities, if a 'complete' DLL were available.

Of course I could use VBA to export the required values to an .exe
that does the modelling, but it would be quite neat to do the whole
think in just Excel (plus a dll!)

I guess it may be possible using chart objects and updating the values
within a looping macro, but that wouldn't be quite as smoothly
animated, and it would be limited to the graphical objects supplied,
no pixels etc.