[wxhaskell-devel] using graphicscontext inside a paint event

[Kristof B. <kr...@re...>]

Hi,

I need to use a graphicpath to draw bezier curves, but wxhaskell doesn't 
allow
me to create a graphicscontext from a paint event.

The reason is the type of the function:

graphicsContextCreate :: WindowDC a -> IO (GraphicsContext ())

while the paint event callback takes a DC () as argument, which is more
general.  It seem wxwidgets needs to know the type of the DC to create
a graphicscontext.  Also wxwidgets 2.8 doesn't have a function to create
one from a  memoryDC, but 3.0 has.

One solution I came up with would be to replace DC () in the paint-event
to  MemoryDC (), since it's double buffered, and to PaintDC in a paint-raw
event.  This callback would also work with a more general function.
Unfortunately it fails on Mac-OS since no memoryDc is used in the paint 
callback.

And it still feels like a low level solution, it would be nicer to have 
a higher level
API that can abstract away these problems.  Maybe making a new paint
callback that already includes the graphiccontext?  Also creating a
graphicspath from a haskell datatype would be nice.

I am willing to help coding this functionality.

Regards,
Kristof Bastiaensen