Example writing onto existing numpy buffer dies

We can confirm the problem raised by stuaxo on Feb 19, 2015. Running the same code with numpy 1.11.1 and 1.9.1 gives the same error with cairocffi. However, if we switch to the cffi-from-buffer branch it gives another error.

Output from cairocffi (branch cffi-from-buffer):

ValueError                                Traceback (most recent call last)
/home/a000680/dev/cairocffi_example.py in <module>()
     32 data = numpy.zeros((width, height, 4), dtype=numpy.uint8)
     33 surface = cairo.ImageSurface.create_for_data(
---> 34     data, cairo.FORMAT_ARGB32, width, height)
     35 cr = cairo.Context(surface)
     36 

/home/a000680/usr/src/cairocffi/cairocffi/surfaces.py in create_for_data(cls, data, format, width, height, stride)
    665 
    666         """
--> 667         return cls(format, width, height, data, stride)
    668 
    669     @staticmethod

/home/a000680/usr/src/cairocffi/cairocffi/surfaces.py in __init__(self, format, width, height, data, stride)
    657             pointer = cairo.cairo_image_surface_create_for_data(
    658                 ffi.cast('char*', address), format, width, height, stride)
--> 659         Surface.__init__(self, pointer, target_keep_alive=data)
    660 
    661     @classmethod

/home/a000680/usr/src/cairocffi/cairocffi/surfaces.py in __init__(self, pointer, target_keep_alive)
    138         self._pointer = ffi.gc(pointer, cairo.cairo_surface_destroy)
    139         self._check_status()
--> 140         if target_keep_alive not in (None, ffi.NULL):
    141             keep_alive = KeepAlive(target_keep_alive)
    142             _check_status(cairo.cairo_surface_set_user_data(

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

If you on line 140 change to the following:

        import numpy as np
        if np.all(target_keep_alive) not in (None, ffi.NULL):

The code seems to run correctly.

Alternatively we saw that we could get the example to run also with the master branch provided you flatten the data (data.ravel() instead of data as the first argument to create_for_data()) and do the following fix in surface.py in the ImageSurface class:

    def __init__(self, format, width, height, data=None, stride=None, tka=True):
        if data is None:
            pointer = cairo.cairo_image_surface_create(format, width, height)
        else:
            if stride is None:
                stride = self.format_stride_for_width(format, width)
            address, length = from_buffer(data)
            if length < stride * height:
                raise ValueError('Got a %d bytes buffer, needs at least %d.'
                                 % (length, stride * height))
            pointer = cairo.cairo_image_surface_create_for_data(
                ffi.cast('char*', address), format, width, height, stride)
        Surface.__init__(self, pointer, target_keep_alive=tka)

[xy-23]

I change this:

return obj.array_interface[‘data’][0], sum(obj,shape)

into this: return ctypes.addressof(ctypes.c_char.from_buffer(obj)), reduce(lambda x, y: x*y , obj.shape)

and change this:

    def __init__(self, pointer, target_keep_alive=None):
        self._pointer = ffi.gc(
            pointer, _keepref(cairo, cairo.cairo_surface_destroy))
        self._check_status()
        if target_keep_alive not in (None, ffi.NULL):
            keep_alive = KeepAlive(target_keep_alive)
            _check_status(cairo.cairo_surface_set_user_data(
                self._pointer, SURFACE_TARGET_KEY, *keep_alive.closure))
            keep_alive.save()

into this: (add .any())

    def __init__(self, pointer, target_keep_alive=None):
        self._pointer = ffi.gc(
            pointer, _keepref(cairo, cairo.cairo_surface_destroy))
        self._check_status()
        if target_keep_alive.any() not in (None, ffi.NULL):
            keep_alive = KeepAlive(target_keep_alive)
            _check_status(cairo.cairo_surface_set_user_data(
                self._pointer, SURFACE_TARGET_KEY, *keep_alive.closure))
            keep_alive.save()

and it works successfully. btw, don’t forget from functools import reduce

[liZe]

Closed by #152.