Re: [Pyobjc-dev] NSGraphicsContext.graphicsPort

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

On 19-apr-2005, at 18:13, Robert Kern wrote:

> Ronald Oussoren wrote:
>
>
>> It is not. What's more acceptable is to introduce a callback  
>> function that is used
>> to construct a CGContextPtr proxy. PyObjC would ship with a  
>> callback function that
>> uses the sillySwigThing code, you could replace that by a function  
>> that created instances
>> of your CG-wrapper.
>>
>
> Okay, what would this callback function take? The sillySwigThing  
> string? A Python long?

A python long. However, I've just realised that adding a custom  
callback is not necessary.
PyObjC contains enough generic machinery to reach our goal (see below).

>
> Will this callback get attached to NSGraphicsContext? or a module?  
> or just passed in as an argument to the method?

The easiest way is using PyObjC's C-API (although the required header  
file currently not installed). As you're writing
an extension module the additional C code shouldn't be a problem.

Annoyingly the API that should be used is slightly flawed, but that  
is easily fixed.

1) change the signature for NSGraphicsContext.graphicsPort (in Lib/ 
AppKit/_AppKitSignatures.py).

The signature currently says that the returntype is 'void*', this  
should be CGContextRef.

2) write two C/Pyrex functions, one for converting from Python to C  
and one for converting from C to Python.

These functions convert from MacPython wrappers to CF types and back:

     static PyObject*
     CF_to_py(void* cfValue)
     {
         return PyObjC_IDToCFType((id)cfValue);
     }

     static int
     py_to_CF(PyObject* obj, void* output)
     {
         id tmp = PyObjC_CFTypeToID(obj);
         if (tmp == NULL && PyErr_Occurred()) {
                 return -1;
         }
         *(void**)output = tmp;
         return 0;
     }

3) call PyObjCPointerWrapper_Register (from C)

    r = PyObjCPointerWrapper_Register(@encode(CFURLRef),
                 (PyObjCPointerWrapper_ToPythonFunc)CF_to_py,
                 (PyObjCPointerWrapper_FromPythonFunc)py_to_CF);
    if (r == -1) FAIL

4) Remove the C-wrappers for -graphicsPort from the _AppKit extension  
module and implement the
default wrappers for CGContextRef (e.g. step 2, but for Apple's  
CoreGraphics wrappers).

I'll do this (and step 1) later today.

>
>> For additional bonus points: harass me or Bob enough to finally  
>> work on extending
>> PyObjC to work with CoreFoundation and use that work to wrap  
>> CoreGraphics.
>>
>
> Wrap it again? Pass.

I was only half serious. PyObjC will contain wrappers for CF and  
friends in the future, but that's
a lot more work than the fix I sketched above.

Ronald