scummvm/graphics/palette.h

/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.

 * This program 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 General Public License for more details.

 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * $URL$
 * $Id$
 *
 */

#ifndef GRAPHICS_PALETTE_H
#define GRAPHICS_PALETTE_H

#include "common/noncopyable.h"

/**
 * The PaletteManager is part of the OSystem backend API and responsible
 * for handling the (possibly emulated) "hardware" palette needed for
 * many old games (e.g. in EGA and VGA mode).
 *
 * By itself it is a pure abstract class, i.e. an "interface"; you can
 * use the OSystem::getPaletteManager() method to obtain an instance
 * that you can use to perform actual palette modifications.
 */
class PaletteManager : Common::NonCopyable {
public:
	virtual ~PaletteManager() {}

	/**
	 * Replace the specified range of the palette with new colors.
	 * The palette entries from 'start' till (start+num-1) will be replaced - so
	 * a full palette update is accomplished via start=0, num=256.
	 *
	 * The palette data is specified in interleaved RGBA format. That is, the
	 * first byte of the memory block 'colors' points at is the red component
	 * of the first new color; the second byte the green component of the first
	 * new color; the third byte the blue component, the last byte to the alpha
	 * (transparency) value. Then the second color starts, and so on. So memory
	 * looks like this: R1-G1-B1-A1-R2-G2-B2-A2-R3-...
	 *
	 * @param colors	the new palette data, in interleaved RGBA format
	 * @param start		the first palette entry to be updated
	 * @param num		the number of palette entries to be updated
	 *
	 * @note It is an error if start+num exceeds 256, behaviour is undefined
	 *       in that case (the backend may ignore it silently or assert).
	 * @note It is an error if this function gets called when the pixel format
	 *       in use (the return value of getScreenFormat) has more than one
	 *       byte per pixel.
	 * @note The alpha value is not actually used, and future revisions of this
	 *       API are probably going to remove it.
	 *
	 * @see getScreenFormat
	 */
	virtual void setPalette(const byte *colors, uint start, uint num) = 0;

	/**
	 * Grabs a specified part of the currently active palette.
	 * The format is the same as for setPalette.
	 *
	 * This should return exactly the same RGB data as was setup via previous
	 * setPalette calls.
	 *
	 * For example, for every valid value of start and num of the following
	 * code:
	 *
	 * byte origPal[num*4];
	 * // Setup origPal's data however you like
	 * g_system->setPalette(origPal, start, num);
	 * byte obtainedPal[num*4];
	 * g_system->grabPalette(obtainedPal, start, num);
	 *
	 * the following should be true:
	 *
	 * For each i < num : memcmp(&origPal[i*4], &obtainedPal[i*4], 3) == 0
	 * (i is an uint here)
	 *
	 * @see setPalette
	 * @param colors	the palette data, in interleaved RGBA format
	 * @param start		the first platte entry to be read
	 * @param num		the number of palette entries to be read
	 *
	 * @note It is an error if this function gets called when the pixel format
	 *       in use (the return value of getScreenFormat) has more than one
	 *       byte per pixel.
	 *
	 * @see getScreenFormat
	 */
	virtual void grabPalette(byte *colors, uint start, uint num) = 0;
};

#endif