OpenGL -- DDS 加载

使用:
loadDDS(“uvmap.DDS”);

---

实现:

#define FOURCC_DXT1 0x31545844 // Equivalent to "DXT1" in ASCII
#define FOURCC_DXT3 0x33545844 // Equivalent to "DXT3" in ASCII
#define FOURCC_DXT5 0x35545844 // Equivalent to "DXT5" in ASCII

GLuint loadDDS(const char * imagepath)
{
    unsigned char header[124];

    FILE *fp; 

    /* try to open the file */ 
    fp = fopen(imagepath, "rb"); 
    if (fp == NULL)
    {
        printf("%s could not be opened. Are you in the right directory ? Don't forget to read the FAQ !\n", imagepath); getchar(); 
        return 0;
    }

    /* verify the type of file */ 
    char filecode[4]; 
    fread(filecode, 1, 4, fp); 
    if (strncmp(filecode, "DDS ", 4) != 0) 
    {
        fclose(fp); 
        return 0; 
    }

    /* get the surface desc */ 
    fread(&header, 124, 1, fp); 

    unsigned int height      = *(unsigned int*)&(header[8 ]);
    unsigned int width       = *(unsigned int*)&(header[12]);
    unsigned int linearSize  = *(unsigned int*)&(header[16]);
    unsigned int mipMapCount = *(unsigned int*)&(header[24]);
    unsigned int fourCC      = *(unsigned int*)&(header[80]);

    unsigned char * buffer;
    unsigned int bufsize;
    /* how big is it going to be including all mipmaps? */ 
    bufsize = mipMapCount > 1 ? linearSize * 2 : linearSize; 
    buffer = (unsigned char*)malloc(bufsize * sizeof(unsigned char)); 
    fread(buffer, 1, bufsize, fp); 
    /* close the file pointer */ 
    fclose(fp);

    unsigned int components  = (fourCC == FOURCC_DXT1) ? 3 : 4; 
    unsigned int format;
    switch(fourCC) 
    { 
    case FOURCC_DXT1: 
        format = GL_COMPRESSED_RGBA_S3TC_DXT1_EXT; 
        break; 
    case FOURCC_DXT3: 
        format = GL_COMPRESSED_RGBA_S3TC_DXT3_EXT; 
        break; 
    case FOURCC_DXT5: 
        format = GL_COMPRESSED_RGBA_S3TC_DXT5_EXT; 
        break; 
    default: 
        free(buffer); 
        return 0; 
    }

    // Create one OpenGL texture
    GLuint textureID;
    glGenTextures(1, &textureID);

    // "Bind" the newly created texture : all future texture functions will modify this texture
    glBindTexture(GL_TEXTURE_2D, textureID);
    glPixelStorei(GL_UNPACK_ALIGNMENT,1);   

    unsigned int blockSize = (format == GL_COMPRESSED_RGBA_S3TC_DXT1_EXT) ? 8 : 16; 
    unsigned int offset = 0;

    /* load the mipmaps */ 
    for (unsigned int level = 0; level < mipMapCount && (width || height); ++level) 
    { 
        unsigned int size = ((width+3)/4)*((height+3)/4)*blockSize; 
        glCompressedTexImage2D(GL_TEXTURE_2D, level, format, width, height,  
            0, size, buffer + offset); 

        offset += size; 
        width  /= 2; 
        height /= 2; 

        // Deal with Non-Power-Of-Two textures. This code is not included in the webpage to reduce clutter.
        if(width < 1) width = 1;
        if(height < 1) height = 1;
    } 

    free(buffer); 
    return textureID;
}