source: mainline/uspace/dist/src/bithenge/gif/gif.bh

#
# Copyright (c) 2012 Vojtech Horky
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#
# - Redistributions of source code must retain the above copyright
#   notice, this list of conditions and the following disclaimer.
# - Redistributions in binary form must reproduce the above copyright
#   notice, this list of conditions and the following disclaimer in the
#   documentation and/or other materials provided with the distribution.
# - The name of the author may not be used to endorse or promote products
#   derived from this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
# OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
# IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
# NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
# THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#

#
# Graphics Interchange Format (image/gif)
#


transform chars(len) = ascii <- known_length(len);
transform word = uint16le;



transform gif_signature = chars(3);

transform gif_version = chars(3);

transform gif_color_map_entry = struct {
        .red <- uint8;
        .green <- uint8;
        .blue <- uint8;
};

transform gif_color_map(length) = repeat(length) {
        gif_color_map_entry
};

transform gif_color_map_from_bits_per_pixel(bits_per_pixel) = struct {
        # We need to emulate missing << operator
        switch (bits_per_pixel) {
                1: { <- gif_color_map(2); };
                2: { <- gif_color_map(4); };
                3: { <- gif_color_map(8); };
                4: { <- gif_color_map(16); };
                5: { <- gif_color_map(32); };
                6: { <- gif_color_map(64); };
                7: { <- gif_color_map(128); };
                8: { <- gif_color_map(256); };
        }
};


# Process GIF data block:
#  - first byte denotes block size (.length)
#  - followed by .length bytes of the actual data (not processed here)
#  - followed by next block or terminator (zero)
transform generic_data_block = do {
        struct {
                .length <- uint8;
                .has_next <- nonzero_boolean <- (.length);
                if (.has_next) {
                        .data <- known_length(.length);
                }
        }
} while (.has_next);


transform gif_image_block = struct {
        .left <- word;
        .top <- word;
        .width <- word;
        .height <- word;

        <- struct {
                .use_local_color_map <- bit;
                .interlacing <- bit;
                .reserved_bits <- uint_be(3);
                .bits_per_pixel <- (in + 1) <- uint_be(3);
        } <- bits_be <- known_length(1);

        if (.use_local_color_map) {
                .local_color_map <- gif_color_map_from_bits_per_pixel(.bits_per_pixel);
        }

        .lzw_initial_size <- uint8;
        .lzw_data <- generic_data_block;
};

# TODO: interpret known extensions
transform gif_extension = struct {
        .function <- uint8;
        .data <- generic_data_block;
};

# Switch over known blocks (image, extensions, end)
transform gif_block = struct {
        .kind <- uint8;
        switch (.kind) {
                33: { # exclamation mark -> extension block
                        .extension <- gif_extension;
                };
                44: { # comma -> image
                        .image <- gif_image_block;
                };
                59: { # semicolon -> terminator
                        .after_terminator <- repeat { uint8 };
                };
                else: {
                        .unknown <- repeat { uint8 };
                };
        }
};

transform main = struct {
        .signature <- gif_signature;
        .version <- gif_version;
        .width <- word;
        .height <- word;
        <- struct {
                .global_color_map_exists <- bit;
                .color_resolution <- uint_be(3);
                .reserved_bit <- uint_be(1);
                .bits_per_pixel <- (in + 1) <- uint_be(3);
        } <- bits_be <- known_length(1);
        .background_color_index <- uint8;
        .reserved <- uint8;
        if (.global_color_map_exists) {
                .global_color_map <- gif_color_map_from_bits_per_pixel(.bits_per_pixel);
        }
        .blocks <- repeat {
                gif_block
        };
};