ios_project/proj.ios_mac/cocos2d-x/cocos/base/etc2.cpp

/****************************************************************************
 Copyright (c) 2010-2012 cocos2d-x.org
 Copyright (c) 2013-2016 Chukong Technologies Inc.
 Copyright (c) 2017-2018 Xiamen Yaji Software Co., Ltd.
 
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 of this software and associated documentation files (the "Software"), to deal
 in the Software without restriction, including without limitation the rights
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 furnished to do so, subject to the following conditions:
 
 The above copyright notice and this permission notice shall be included in
 all copies or substantial portions of the Software.
 
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 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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#include "base/etc2.h"
#include <stdint.h>
#include <string.h>

static const char kMagic[] = { 'P', 'K', 'M', ' ', '2', '0' };

static const etc2_uint32 ETC2_PKM_FORMAT_OFFSET = 6;
static const etc2_uint32 ETC2_PKM_ENCODED_WIDTH_OFFSET = 8;
static const etc2_uint32 ETC2_PKM_ENCODED_HEIGHT_OFFSET = 10;
static const etc2_uint32 ETC2_PKM_WIDTH_OFFSET = 12;
static const etc2_uint32 ETC2_PKM_HEIGHT_OFFSET = 14;

static void writeBEUint16(etc2_byte* pOut, etc2_uint32 data) {
    pOut[0] = (etc2_byte) (data >> 8);
    pOut[1] = (etc2_byte) data;
}

static etc2_uint32 readBEUint16(const etc2_byte* pIn) {
    return (pIn[0] << 8) | pIn[1];
}

// Check if a PKM header is correctly formatted.

etc2_bool etc2_pkm_is_valid(const etc2_byte* pHeader) {
    if (memcmp(pHeader, kMagic, sizeof(kMagic))) {
        return false;
    }
    etc2_uint32 format = readBEUint16(pHeader + ETC2_PKM_FORMAT_OFFSET);
    etc2_uint32 encodedWidth = readBEUint16(pHeader + ETC2_PKM_ENCODED_WIDTH_OFFSET);
    etc2_uint32 encodedHeight = readBEUint16(pHeader + ETC2_PKM_ENCODED_HEIGHT_OFFSET);
    etc2_uint32 width = readBEUint16(pHeader + ETC2_PKM_WIDTH_OFFSET);
    etc2_uint32 height = readBEUint16(pHeader + ETC2_PKM_HEIGHT_OFFSET);
    return (format == ETC2_RGB_NO_MIPMAPS || format == ETC2_RGBA_NO_MIPMAPS) &&
            encodedWidth >= width && encodedWidth - width < 4 &&
            encodedHeight >= height && encodedHeight - height < 4;
}

// Read the image width from a PKM header

etc2_uint32 etc2_pkm_get_width(const etc2_byte* pHeader) {
    return readBEUint16(pHeader + ETC2_PKM_WIDTH_OFFSET);
}

// Read the image height from a PKM header

etc2_uint32 etc2_pkm_get_height(const etc2_byte* pHeader){
    return readBEUint16(pHeader + ETC2_PKM_HEIGHT_OFFSET);
}

etc2_uint32 etc2_pkm_get_format(const uint8_t* pHeader) {
    return readBEUint16(pHeader + ETC2_PKM_FORMAT_OFFSET);
}