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Adding a new io backend

of backend requirements

To add support for a new IO backend the following is required:

• a format tag, to identify the image format, derived from boost::gil::format_tag
• boolean meta function is_supported<PixelType,FormatTag> must be implemented for the new format tag
• explicit specialisation of image_read_info<FormatTag> must be provided, containing runtime information available before/at reading the image
• explicit specialisation of image_write_info<FormatTag> must be provided, containing runtime encoding parameters for writing an image
• An image reader must be specialized:

template<typename IODevice, typename ConversionPolicy>

struct boost::gil::reader<IODevice,FormatTag,ConversionPolicy>

{

reader( IODevice & device )

reader( IODevice & device, typename ConversionPolicy::color_converter_type const& cc )

image_read_info<FormatTag> get_info();

template<typename Image>

void read_image( Image &, point_t const& top_left );

template<typename View>

void read_view( View &, point_t const& top_left );

};

• An image writer must be specialized:

\template <typename IODevice>

struct boost::gil::writer<IODevice,FormatTag>

{

writer( IODevice & device )

template<typename View>

void apply( View const&, point_t const& top_left );

template<typename View>

void apply( View const&, point_t const& top_left, image_write_info<FormatTag> const& );

};

Or instead of the items above implement overloads of read_view, read_and_convert_view, read_image, read_and_convert_image, write_view and read_image_info.

Interface of the ConversionPolicy

There are two different conversion policies in use, when reading images: read_and_convert<ColorConverter> and read_and_no_convert. ColorConverter can be a user defined color converter.

struct ConversionPolicy

{

template<typename InputIterator,typename OutputIterator>

void read( InputIterator in_begin, InputIterator in_end,

OutputIterator out_end );

};

Methods like read_view and read_image are supposed to bail out with an exception instead of converting the image

Concept of IO Device

A Device is simply an object used to read and write data to and from a stream. The IODevice was added as a template paramter to be able to replace the file_name access functionality. This is only an interim solution, as soon as boost provides a good IO library, interfaces/constraints provided by that library could be used.

concept IODevice

{

void IODevice::read( unsigned char* data, int count );

void IODevice::write( unsigned char* data, int count );

void IODevice::seek(long count, int whence);

void IODevice::flush();

};

For the time being a boolean meta function must be specialized:

namespace boost{namespace gil{namespace detail{

template<typename Device>

struct detail::is_input_device;

}}}

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