[Pyobjc-dev] using a CGContextRef

[Bobby P. <bob...@gm...>]

Hi,  I'm relatively new to this, but I've been trying for the past 2  
days to get this working and have scoured the internet, so I figured  
its time to try the mailing list (I've looked through some of these  
archives, too).

I am trying to add support to pyCairo for Cairo's Quartz backend.   
Specifically I am working on a wrapper function that needs the  
CGContextRef for the current screen to create the Cairo surface.

In the test program (reproduced below), i get the context using  
NSGraphicsContext.currentContext().graphicsPort() and pass this to the  
function to create the surface, which is written in C. (As an aside, I  
read in some older mails to import Quartz when the  
applicationDidFinishLaunching method in a delagate was invoked.   
drawRect for me was being called before that, so I switched it to the  
view's init function and it seems to work fine).  It took me a while  
to figure out the format strings in PyArg_ParseTuple and I may still  
not be doing them right... but the long and short of it is I can't get  
the CGContextRef in C from Python.  I tried typecasting the PyObject  
to CGContextRef, and I've tried PyCObject_AsVoidPtr (but the PyObject  
passed is of the type 'CGContext' and not a PyCObject...  so I'm not  
sure what to do.

I am new, so if something like this is explained somewhere (or there  
is a better place to go for help), please let me know.  Thanks!  (and  
I hope this email formatting comes through alright...)

yours,
Bobby

----------

simplified test class:
from Foundation import *
from AppKit import *

import cairo

class CairoView(NSView):
     def initWithFrame_(self, frame):
         self = super(CairoView, self).initWithFrame_(frame)
         if self:
             import Quartz
         return self

     def drawRect_(self, rect):
         context = NSGraphicsContext.currentContext().graphicsPort()
         surface = cairo.QuartzSurface(context, 200, 200)


wrapper function:
static PyObject *
quartz_surface_new (PyTypeObject *type, PyObject *args, PyObject *kwds)
{

     PyObject *pyContext;
     float width, height;

     if (!PyArg_ParseTuple (args, "Off:QuartzSurface.__new__",
                            &pyContext, &width, &height))
         return NULL;

     CGContextRef ctx = (CGContextRef)(void *)pyContext;

	// Make the CGContext coordinate system sane, as expected by Cairo
	CGContextTranslateCTM (ctx, 0.0, height);
	CGContextScaleCTM (ctx, 1.0, -1.0);
	

     return PycairoSurface_FromSurface (
                                         
cairo_quartz_surface_create_for_cg_context (ctx, width, height),
                                        NULL);
}