Writing plugins - How to questions..

Graphics
Does TLB simply allocate a square of bar for the plugin icon to
appear in?.. or is it a complex interaction, where TLB does the
actual display of various component icons on behalf of the plugin?

Here is definition of draw function:

Code:

STDMETHODIMP ITlbButton::Draw(HANDLE hDC, RECT *rcItem)

To draw button you implement this function. hDC is a handle to a device context (DC). rcItem is poiter to the RECT struct where you must draw your button. All is simple

Code:

Does TLB pass mouse click data to the plugin (say for the
Winamp plugin, where there are various buttons?)  Or is the
plugin detecting and acting on these by itself?

The same way. ITlbButton interface have some functions to handle mouse events:

Code:

STDMETHODIMP OnMouseOver(long keys, int x, int y);
STDMETHODIMP OnMouseLeave(long keys);
STDMETHODIMP OnMouseEnter(long keys, int x, int y);
STDMETHODIMP OnLButtonDown(long key, int x, int y);
STDMETHODIMP OnLButtonUp(long key, int x, int y);

TLB call these functions to notify plugin about mouse events.

I assume plugin configuration dialogues are entirely
independant of TLB?

All dialogs and windows are independant of TLB. The only thing TLB supply plugins is stream to save and load data of plugins:

Code:

STDMETHODIMP Load(IStream *data);
STDMETHODIMP Save(IStream *data);

Also note that plugin does not have own window.