/* *****************************************************************************
 * libg1m/format/std/picture.h -- the picture formats description.
 * Copyright (C) 2017 Thomas "Cakeisalie5" Touhey <thomas@touhey.fr>
 *
 * This file is part of libg1m.
 * libg1m is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 3.0 of the License,
 * or (at your option) any later version.
 *
 * libg1m is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with libg1m; if not, see <http://www.gnu.org/licenses/>.
 * ************************************************************************** */
#ifndef LIBG1M_FORMAT_STD_PICTURE_H
# define LIBG1M_FORMAT_STD_PICTURE_H
# include <stdint.h>
# pragma pack(1)

/* ************************************************************************** */
/*  G3P: pictures for Prizm                                                   */
/* ************************************************************************** */
/* G3P are pictures for fx-CG. They start with a Standard Header, and
 * a Standard Picture Header.
 *
 * This mysteries over this format have been unraveled by many, but I'm using
 * Simon Lothar's documentation and Kerm Martian's articles.
 *
 * Prizm pictures (G3P) support several image depths (encodings): */

# define g3p_color_4bit  0x03
# define g3p_color_16bit 0x10

/* After the standard headers, comes the specific header: */

struct g3p_subheader {
	/* magic sequence? is: 0x00, 0x01, 0x00, 0x00 */
	uint8_t magic[4];

	/* size of the image data + footer */
	uint32_t df_size;

	/* w0t */
	uint8_t _unknown0[2];

	/* width */
	uint16_t width;

	/* height */
	uint16_t height;

	/* color depth - see `g3p_colorsize` */
	uint16_t color_depth;

	/* undocumented, again */
	uint8_t _unknown1[4];

	/* length of the image data + 6
	 * the 6 bytes are:
	 * - the 16-bit generator ID at the beginning;
	 * - the 32-bit checksum at the end of the data. */
	uint32_t data_size;

	/* Generator ID */
	uint16_t generator_id;
};

/* The generator ID is a 16-bit ID giving information about the picture
 * generator. The known IDs are the following: */

# define g3p_id_casio    0x3C1B
# define g3p_id_unknown0 0x388D
# define g3p_id_unknown1 0x789C
# define g3p_id_unknown2 0x3E93

/* Then we have the deflated image data, which is `data_size - 6` sized
 * (see the `data_size` comment above for more explanation).
 *
 * Before inflating, you should check if the image is obfuscated (Simon Lothar
 * says 'encrypted', I suppose that's more polite). It is if:
 *
 *		(std.obfuscated + 8) & 0xFF != (std.filesize & 0xff00) >> 8
 *
 * If it is, then in order to de-obfuscate, you should do the following
 * operation:
 *
 *		byte = ~((byte << 5) | (byte >> 3)) & 0xFF;
 *
 * Then you can inflate.
 * Once this is done, you can get the next four bytes, also considered as
 * part of the data: the 32-bit adler32 checksum. It is a checksum over the
 * raw, uncompressed data (and is appended to it before deflating/obfuscating).
 *
 * TODO: footers */
/* ************************************************************************** */
/*  C2P: Images for Classpads                                                 */
/* ************************************************************************** */
/* C2P are pictures for CASIO Classpad calculators (fx-CP*). They start with
 * a Standard Header, followed by a Standard Picture Header.
 *
 * Then comes the specific subheader: */

struct c2p_subheader {
	/* "0100" */
	uint8_t magic[4];

	/* footer offset? `filesize - 0x254` */
	uint32_t footer_offset;

	/* unknown */
	uint16_t unknown2;

	/* width (max for screen: 0x136 */
	uint16_t width;

	/* height (max for screen: 0x191) */
	uint16_t height;

	/* undocumented, again */
	uint8_t undocumented2[18];

	/* filesize - 0x258 */
	uint32_t unknown_size3;
};

/* Then there is the zlib header with default compression.
 * The pixels format is R5G6B5.
 *
 * After the image, there is a footer, which is mainly undocumented, but
 * here is what we've got: */

struct c2p_footer {
	/* "0100", again */
	uint8_t magic[4];

	/* and some undocumented stuff */
	uint8_t undocumented[0xE4];
};

# pragma pack()
#endif /* LIBG1M_FORMAT_STD_PICTURE_H */