[MacRuby-devel] MacRuby 0.5 vs. CG Bitmap Context

[Scott Thompson]

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?

Scott

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