====== 009 DDSテクスチャの読み込み ======

===== 概要 =====
DXT1，3、5に対応しています。テクスチャはミップマップを含む様にして下さい。

==== ソースコード ====

<code c>
typedef struct
{
	uint32    uSize;
	uint32    uFlags;
	uint32    uFourCC;
	uint32    uRgbBitCount;
	uint32    uRbitMask;
	uint32    uGbitMask;
	uint32    uBbitMask;
	uint32    uAbitMask;
} DDSPixelFormat;

typedef struct
{
	uint8			uMagic[4];
	uint32			uSize;
	uint32			uFlags;
	uint32			uHeight;
	uint32			uWidth;
	uint32			uPitchOrLinearSize;
	uint32			uDepth;
	uint32			uMipMapCount;
	uint32			uReserved1[11];
	DDSPixelFormat		Ddspf;
	uint32			uCaps1;
	uint32			uCaps2;
	uint32			uReserved2[3];
} DDSHeader;

class DDSUtil
{
public:
	static bool IsDDS( const uint8* _pData )
	{
		const DDSHeader* pHeader = reinterpret_cast<const DDSHeader*>( _pData );
		if( (uint32)pHeader->uMagic != (uint32)DDS_MAGIC )
		{
			return false;
		}
		
		return true;
	}

	static bool Load( const uint8* _pData, GLuint* _textureID, sint32* _width, sint32* _height )
	{
		const uint8* pImage = _pData + sizeof( DDSHeader );
		const DDSHeader* pHeader = reinterpret_cast<const DDSHeader*>( _pData );
		
		GLuint textureName;
		glGenTextures( 1, &textureName );
		glBindTexture( GL_TEXTURE_2D, textureName );
		
		uint32 uWidth = pHeader->uWidth;
		uint32 uHeight = pHeader->uHeight;
		uint32 uFormat;
		
		switch( pHeader->Ddspf.uFourCC )
		{
		case DDS_DXT1:
			{
				uFormat = GL_COMPRESSED_RGBA_S3TC_DXT1_EXT;
			}
			break;
			
		case DDS_DXT3:
			{
				uFormat = GL_COMPRESSED_RGBA_S3TC_DXT3_EXT;
			}
			break;
			
		case DDS_DXT5:
			{
				uFormat = GL_COMPRESSED_RGBA_S3TC_DXT5_EXT;
			}
			break;
		};
		
		sint32 blockSize;
		sint32 offset = 0;
		sint32 uSize = 0;
		// DXT1
		if( uFormat == GL_COMPRESSED_RGBA_S3TC_DXT1_EXT )
		{
			blockSize = 8;
		}
		// DXT3 or DXT5
		else
		{
			blockSize = 16;
		}
		
		for( uint32 i = 0; i < pHeader->uMipMapCount; i++ )
		{
			uSize = ( ( uWidth + 3 ) / 4 ) * ( ( uHeight + 3 ) / 4 ) * blockSize;
			
			glCompressedTexImage2D( GL_TEXTURE_2D, i,
			uFormat, uWidth, uHeight, 0, uSize, pImage + offset );
			
			if( uWidth >> 1 )
			{
				uWidth = (uWidth >> 1);
			}
			else
			{
				uWidth = 1;
			}
			if( uHeight >> 1 )
			{
				uHeight = (uHeight >> 1);
			}
			else
			{
				uHeight = 1;
			}
			offset += uSize;
		}
		
		*_width = pHeader->uWidth;
		*_height = pHeader->uHeight;
		*_textureID = textureName;
		
		return true;
	}
};

</code>