Hi Scott,
On Mar 5, 2010, at 8:34 AM, Scott Thompson wrote:
> I'm using MacRuby to work with CoreGraphics and having some trouble with
> pointers.
>
> My first attempt was to create the data for a bitmap context using
> NSMutableData:
>
> bitmap_data = NSMutableData.alloc.initWithLength(image_data_size)
> bitmap_context = CGBitmapContextCreate(
> bitmap_data.mutableBytes(),
> image_width, image_height,
> 8, image_width,
> gray_color_space, KCGImageAlphaNone)
>
> If I do this, I get an error that "expected instance of Pointer of type 'v',
> got 'C' (TypeError)"
>
> I gather from this that CGBitmapContextCreate was expecting a (void *) and
> got a (UInt8 *). In C I would just type the difference away, but Ruby
> doesn't like ti.
>
> I tried something like:
>
> bitmap_data_ptr = Pointer.new_of_type('v')
> bitmap_data_ptr.assign(bitmap_data.mutableBytes())
>
> This didn't work very well either. I get an error that the system can't do a
> "sizeof" of an unsized type (presumably void *)
>
> I also tried doing similar using CFDataRef (not much difference really). It
> looked like:
>
> bitmap_data = CFDataCreateMutable(nil, image_data_size)
> CFDataSetLength(bitmap_data, image_data_size)
> bitmap_data_ptr = CFDataGetMutableBytePtr(bitmap_data)
> bitmap_context = CGBitmapContextCreate(
> CFDataGetMutableBytePtr(bitmap_data),
> image_width, image_height,
> 8, image_width,
> gray_color_space, KCGImageAlphaNone)
>
> In this case, I get an error that "expected instance of Pointer, got '""'
> (NSMutableString) (TypeError)
>
> Evidently MacRuby sees the return value of CFDataGetMutableBytePtr as being a
> string, subsequently typecasts it as such, and goes on.
>
> Is there anything I can do to typecast the pointers to a type that MacRuby
> will accept?
Unfortunately, the Pointer class currently will not allow you to cast types :(
If you file a bug in Trac we will add this functionality in the next release.
Patches are also welcome :)
In the meantime I would recommend to write this in Objective-C and call it from
MacRuby.
Sorry,
Laurent_______________________________________________
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