加载MD2文件播放角色动画

MD2文件由两个主要部分组成：文件头和数据。

文件头部分：包含模型描述，多边形数，顶点数和动画细节等。
数据部分：组成模型的多边形网格的数据，包括所有的多边形，顶点和纹理数据。

在MD2文件中，所有的多边形都为三角形，且没有其他的实体。
顶点数据定义的不是单帧而是多帧动画。事实上，每个MD2文件包含198帧动画，编号为0－197。

MD2文件头数据结构定义：

// This is the header structure for a Quake II .MD2 file by id Software
typedef struct MD2_HEADER_TYPE
{
    int identifier;          // identifies the file type, should be "IDP2"
    int version;             // version number, should be 8.
    int skin_width;        // width of texture map used for skinning
    int skin_height;       // height of texture map used for skinning
    int framesize;          // number of bytes in a single frame of animation

    int num_skins;        // total number of skins,
                                  // listed by ASCII filename and are available for loading if files are found in full path.

    int num_verts;        // number of vertices in each model frame,
                                // the number of vertices in each frame is always the same.

    int num_textcoords; // total number of texture coordinates in entire file,
                                   // may be larger than the number of vertices.

    int num_polys;        // number of polygons per model, or per frame of animation if you will.

    int num_openGLcmds; // number of openGL commands which can help with rendering optimization,
                          // however, we won't be using them.

    int num_frames;     // total number of animation frames

    // memory byte offsets to actual data for each item

    int offset_skins;       // offset in bytes from beginning of file to the skin array that holds the file name
                                   // for each skin, each file name record is 64 bytes.

    int offset_textcoords;  // offset in bytes from the beginning of file to the texture coordinate array
    int offset_polys;          // offset in bytes from the beginning of file to the polygon mesh
    int offset_frames;     // offset in bytes from the beginning of file to the vertex data for each frame
    int offset_openGLcmds;  // offset in bytes from the beginning of file to the openGL commands
    int offset_end;         // offset in bytes from the beginning of file to end of file
} MD2_HEADER, *MD2_HEADER_PTR;