Indesign SDK - custom draw palette

Indesign doesn't use windows to put together many panels into a palette or to draw the tab of a palette. It uses GDI (or the equivalent on the Mac) to draw everything on screen. IControlView is the interface for a "control", you can navigate the controls tree trough IWidgetParent interface (and GetParent method) and IPanelControlData or IPaletteControlData.

Suppose you have a panel that is subclassed by you, you can ask for the IPaletteControlData, this way:

IPaletteControlData* ppcd = nil;
InterfacePtr<IWidgetParent> parent(this, UseDefaultIID());
if( parent ) {
    ppcd = static_cast<IPaletteControlData*>(parent->QueryParentFor(IID_IPALETTECONTROLDATA));
}
InterfacePtr<IPaletteControlData> pcd(ppcd);
ASSERT(pcd);

Now you can use GetSectionCount and GetSection to retrieve the interface for the wanted control, the first one is the tab, the other is the entire panel. Suppose you want to enumerate the tabs in the palette, you need the PanelControlData for the tabs so:

InterfacePtr<IControlView> tabAreaView(pcd->GetSection(0), UseDefaultIID());
ASSERT(tabAreaView);
InterfacePtr<IPanelControlData> tabAreaCD(tabAreaView, UseDefaultIID());
ASSERT(tabAreaCD);
 
for(int32 idx = 0; idx < tabAreaCD->Length(); idx++) {
	InterfacePtr<IControlView> tabWidget(tabAreaCD->GetWidget(idx), UseDefaultIID());
}

And there you can draw whatever you want on the tab.