A window device context allows drawing into an FXDrawable, such as an on-screen window (i.e. FXWindow and itsderivatives) or an off-screen
image (FXImage and its derivatives). Because
certain hardware resources are locked down, only one FXDCWindow may be locked on a drawable at any
one time.
Construct for painting in response to expose; this sets the clip rectangle
to the exposed rectangle. If an optional code block is provided, the new
device context will be passed into the block as an argument and end will be called automatically when
the block terminates.
Construct for normal drawing; this sets clip rectangle to the whole
drawable. If an optional code block is provided, the new device context
will be passed into the block as an argument and end will be called automatically when
the block terminates.