Re: [Pyobjc-dev] using a CGContextRef

[Ronald O. <ron...@ma...>]

On 14 Nov, 2007, at 2:10, Bobby Powers wrote:

> 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...)

someContext.__cobject__() returns a PyCObject, PyCObject_AsVoidPtr can  
then be used to extract the CGContextRef from C.

Ronald

>
> 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);
> }
>
>
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