[cairo] Re: Notes on cairo/win32

[J. Ali Harlow]

On 13/01/05 22:06:46, J. Ali Harlow wrote:
> On 13/01/05 20:27:43, Owen Taylor wrote:
> 
> > I think that the claim is that the flat API is C++ based too...
> 
> Concern, at least, yes.
> 
> > GpPath *is* defined as a class, but only in the most trivial way.
> > As far as I can see, it's really just an opaque pointer and you
> > could use a C definition like:
> >
> >  typedef struct GpPath_ GpPath;
> >
> > and it should work fine.
> 
> Let's hope you're right. I'll try and have a play tomorrow and see if
> I can put together a gdiplusflat.h which uses opaque pointers or  
> drops functions that take classes that appear to be wrappers  
> themselves (eg., GdipAddPathRectanglesI which probably just wraps
> GdipAddPathRectangleI).

Okay, I've had a quick play. It's possible to produce header files  
which will compile with a C compiler as long as you avoid certain  
functions which use the C++ '&' operator. Mine are pretty raw, but if  
anybody wants them, please shout.

However, in trying to use these headers to compile a test program[1], I  
ran into trouble with trying to lock a bitmap. It seems as though you  
have to have a Rect (which is a class) to lock a bitmap and there is no  
way to create one in C.

Some half-baked ideas for how to proceed:

- It's possible that you could try and hack one up using a structure if  
you assumed that the public members came at the start but I've no idea  
if this would work and in any case it doesn't sound like a sensible way  
to proceed to me.

- We could set aside a hopefully-large-enough block of memory and then  
set and get the clip rect as another gross hack.

- Another possibility would be to try and see if we could pass NULL  
into the locking function. We'd loose the ability to lock a portion of  
a bitmap, but that might be acceptable if it happens to work. It's  
still breaking the published API of course.

- There may be a method of creating a Rect using one of the functions  
which I have excluded because they use the C++ '&' operator. Somebody  
who understands C++ rather more than me (ie., at all) will need to  
advise here.

- Assume we don't need this functionality for cairo and soldier on.

Ali.

[1] http://www.thecodeproject.com/vcpp/gdiplus/edge_detection_in__c.asp