DDS文件格式解析

DDS是DirectDrawSurface的缩写，它是DirectX纹理压缩（DirectX TextureCompression，简称DXTC）的产物。

DXTC减少了纹理内存消耗的50%甚至更多，有3种DXTC的格式可供使用，分别是DXT1，DXT3和DXT5。

DXT1 压缩比例：1:8

压缩比最高，它只有1BitAlpha，Alpha通道信息几乎完全丧失。一般将不带Alpha通道的图片压缩成这种格式。如WorldWind用的卫星图片

DXT3 压缩比例：1:4

使用了4BitAlpha，可以有16个Alpha值，可很好地用于alpha通道锐利、对比强烈的半透和镂空材质。

DXT5 压缩比例：1:4

使用了线形插值的4BitAlpha，特别适合Alpha通道柔和的材质，比如高光掩码材质。

 

dds格式分为2个部分：
1、dds头
2、dxt压缩数据

 

dds的头文件信息如下：

typedef struct _DDCOLORKEY
{
    uint32      dwColorSpaceLowvalue;   // lowboundary of color space that is to
                                        //be treated as Color Key, inclusive
    uint32      dwColorSpaceHighvalue;  // highboundary of color space that is
                                        //to be treated as Color Key, inclusive
} DDCOLORKEY;

typedef struct _DDSCAPS2
{
    uint32      dwCaps;        // capabilities of surface wanted
    uint32      dwCaps2;
    uint32      dwCaps3;
    union
    {
        uint32      dwCaps4;
        uint32      dwVolumeDepth;
    }DUMMYUNIONNAMEN(1);
} DDSCAPS2;

typedef struct _DDPIXELFORMAT
{
    uint32      dwSize;                // size of structure
    uint32      dwFlags;                //pixel format flags
    uint32      dwFourCC;              // (FOURCC code)
    union
    {
        uint32  dwRGBBitCount;          //how many bits per pixel
        uint32  dwYUVBitCount;          //how many bits per pixel
        uint32  dwZBufferBitDepth;      //how many total bits/pixel in z buffer (including any stencilbits)
        uint32  dwAlphaBitDepth;        //how many bits for alpha channels
        uint32  dwLuminanceBitCount;    //how many bits per pixel
        uint32  dwBumpBitCount;        // how many bits per "buxel", total
        uint32  dwPrivateFormatBitCount;// Bits per pixel of private driverformats. Only valid in texture
                                        //format list and if DDPF_D3DFORMAT is set
    }DUMMYUNIONNAMEN(1);
    union
    {