Using Bitmap in controls GUI

How can I use bmp images in the controls? Where can I see examples or read about it?

Is it the correct way to set the background as
Does it load the file dynamically? Or is it use the resource (as vstgui) .

And attaching of a knob to the background should be done as
pGraphics->AttachControl(new IBKnobControl()) ? I need some glue on this as IPlug2 examples seem to use VG only, and working with bmp was intuitive in WDL-OL .

see e.g. IPlugControls example

also the Wiki: