How to use the pyvips.at_least_libvips function in pyvips

    @pytest.mark.skipif(not pyvips.at_least_libvips(8, 5),
                        reason="requires libvips >= 8.5")
    def test_get_fields(self):
        im = pyvips.Image.black(10, 10)
        fields = im.get_fields()
        # we might add more fields later
        assert len(fields) > 10
        assert fields[0] == 'width'

def test_hist_local(self):
        im = pyvips.Image.new_from_file(JPEG_FILE)

        im2 = im.hist_local(10, 10)

        assert im.width == im2.width
        assert im.height == im2.height

        assert im.avg() < im2.avg()
        assert im.deviate() < im2.deviate()

        if pyvips.at_least_libvips(8, 5):
            im3 = im.hist_local(10, 10, max_slope=3)

            assert im.width == im3.width
            assert im.height == im3.height

            assert im3.deviate() < im2.deviate()

def test_gifload(self):
        def gif_valid(im):
            a = im(10, 10)
            assert_almost_equal_objects(a, [33])
            assert im.width == 159
            assert im.height == 203
            assert im.bands == 1

        self.file_loader("gifload", GIF_FILE, gif_valid)
        self.buffer_loader("gifload_buffer", GIF_FILE, gif_valid)

        # 'n' param added in 8.5
        if pyvips.at_least_libvips(8, 5):
            x1 = pyvips.Image.new_from_file(GIF_ANIM_FILE)
            x2 = pyvips.Image.new_from_file(GIF_ANIM_FILE, n=2)
            assert x2.height == 2 * x1.height
            page_height = x2.get("page-height")
            assert page_height == x1.height

            x2 = pyvips.Image.new_from_file(GIF_ANIM_FILE, n=-1)
            assert x2.height == 5 * x1.height

            x2 = pyvips.Image.new_from_file(GIF_ANIM_FILE, page=1, n=-1)
            assert x2.height == 4 * x1.height

    @pytest.mark.skipif(not pyvips.at_least_libvips(8, 5),
                        reason="requires libvips >= 8.5")
    def test_thumbnail(self):
        im = pyvips.Image.thumbnail(JPEG_FILE, 100)

        assert im.height == 100
        assert im.bands == 3
        assert im.bands == 3

        # the average shouldn't move too much
        im_orig = pyvips.Image.new_from_file(JPEG_FILE)
        assert abs(im_orig.avg() - im.avg()) < 1

        # make sure we always get the right width
        for height in range(440, 1, -13):
            im = pyvips.Image.thumbnail(JPEG_FILE, height)
            assert im.height == height

# perhaps
        # assert im.width == width * 2
        # assert im.height == height * 2

        # all-frames should load every frame of the animation
        # (though all-frames is deprecated)
        im = pyvips.Image.magickload(GIF_ANIM_FILE)
        width = im.width
        height = im.height
        im = pyvips.Image.magickload(GIF_ANIM_FILE, all_frames=True)
        assert im.width == width
        assert im.height == height * 5

        # page/n let you pick a range of pages
        # 'n' param added in 8.5
        if pyvips.at_least_libvips(8, 5):
            im = pyvips.Image.magickload(GIF_ANIM_FILE)
            width = im.width
            height = im.height
            im = pyvips.Image.magickload(GIF_ANIM_FILE, page=1, n=2)
            assert im.width == width
            assert im.height == height * 2
            page_height = im.get("page-height")
            assert page_height == height

        # should work for dicom
        im = pyvips.Image.magickload(DICOM_FILE)
        assert im.width == 128
        assert im.height == 128
        # some IMs are 3 bands, some are 1, can't really test
        # assert im.bands == 1

#
            # * in API mode, we must have 8.6+ and use set_blob_free to
            #   attach the metadata to avoid leaks
            # * pre-8.6, we just pass a NULL free pointer and live with the
            #   leak
            #
            # this is because in API mode you can't pass a builtin (what
            # vips_lib.g_free() becomes) as a parameter to ffi.callback(), and
            # vips_value_set_blob() needs a callback for arg 2
            #
            # additionally, you can't make a py def which calls g_free() and
            # then use the py def in the callback, since libvips will trigger
            # these functions during cleanup, and py will have shut down by
            # then and you'll get a segv

            if at_least_libvips(8, 6):
                vips_lib.vips_value_set_blob_free(self.gvalue,
                                                  memory, len(value))
            else:
                if pyvips.API_mode:
                    vips_lib.vips_value_set_blob(self.gvalue,
                                                 ffi.NULL, memory, len(value))
                else:
                    vips_lib.vips_value_set_blob(self.gvalue,
                                                 glib_lib.g_free,
                                                 memory, len(value))
        else:
            raise Error('unsupported gtype for set {0}, fundamental {1}'.
                        format(type_name(gtype), type_name(fundamental)))

exist. See :class:`GValue`.

        Args:
            name (str): The name of the piece of metadata to get the type of.

        Returns:
            The ``GType``, or 0.

        Raises:
            None

        """

        # on libvips before 8.5, property types must be fetched separately,
        # since built-in enums were reported as ints
        if not at_least_libvips(8, 5):
            gtype = super(Image, self).get_typeof(name)
            if gtype != 0:
                return gtype

        return vips_lib.vips_image_get_typeof(self.pointer, _to_bytes(name))

def fetch(self, x, y, w, h):
        """Fill a region with pixel data.

        Pixels are filled with data!

        Returns:
            Pixel data.

        Raises:
            :class:`.Error`

        """

        if not at_least_libvips(8, 8):
            raise Error('libvips too old')

        psize = ffi.new('size_t *')
        pointer = vips_lib.vips_region_fetch(self.pointer, x, y, w, h, psize)
        if pointer == ffi.NULL:
            raise Error('unable to fetch from region')

        pointer = ffi.gc(pointer, glib_lib.g_free)
        return ffi.buffer(pointer, psize[0])

def width(self):
        """Width of pixels held by region."""
        if not at_least_libvips(8, 8):
            raise Error('libvips too old')

        return vips_lib.vips_region_width(self.pointer)

would fetch the image orientation.

        Args:
            name (str): The name of the piece of metadata to get.

        Returns:
            The metadata item as a Python value.

        Raises:
            :class:`.Error`

        """

        # with old libvips, we must fetch properties (as opposed to
        # metadata) via VipsObject
        if not at_least_libvips(8, 5):
            gtype = super(Image, self).get_typeof(name)
            if gtype != 0:
                return super(Image, self).get(name)

        gv = GValue()
        result = vips_lib.vips_image_get(self.pointer, _to_bytes(name),
                                         gv.pointer)
        if result != 0:
            raise Error('unable to get {0}'.format(name))

        return gv.get()