Opengl纹理映射和图像重排

int LoadTexture(char *filename,int alpha) 
{
    using namespace std;
    int i, j=0; //Index variables
    static int num_texture;
    ifstream l_file(filename);
    unsigned char *l_texture; //The pointer to the memory zone in which we will load the texture

    // windows.h gives us these types to work with the Bitmap files
    BITMAPFILEHEADER fileheader; 
    BITMAPINFOHEADER infoheader;
    RGBTRIPLE rgb;

    num_texture++; // The counter of the current texture is increased

    if(!l_file) return (-1); // Open the file for reading

    l_file.read(reinterpret_cast<char *>(&fileheader), sizeof(fileheader)); // Read the fileheader

    //fseek(l_file, sizeof(fileheader), SEEK_SET); // Jump the fileheader
    l_file.read(reinterpret_cast<char *>(&infoheader), sizeof(infoheader)); // and read the infoheader

    // Now we need to allocate the memory for our image (width * height * color deep)
    l_texture = new byte [infoheader.biWidth * infoheader.biHeight * 4];
    // And fill it with zeros
    memset(l_texture, 0, infoheader.biWidth * infoheader.biHeight * 4);

    // At this point we can read every pixel of the image
    for (i=0; i < infoheader.biWidth*infoheader.biHeight; i++)
    {            
          // We load an RGB value from the file
          l_file.read(reinterpret_cast<char *>(&rgb), sizeof(rgb)); 

          // And store it
          l_texture[j+0] = rgb.rgbtRed; // Red component
          l_texture[j+1] = rgb.rgbtGreen; // Green component
          l_texture[j+2] = rgb.rgbtBlue; // Blue component
          l_texture[j+3] = alpha; // Alpha value
          j += 4; // Go to the next position
     }

     l_file.close(); // Closes the file stream

     glBindTexture(GL_TEXTURE_2D, num_texture); // Bind the ID texture specified by the 2nd parameter

     // The next commands sets the texture parameters
     glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT); // If the u,v coordinates overflow the range 0,1 the image is repeated
     glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
     glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR); // The magnification function (\"linear\" produces better results)
     glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR); //The minifying function

     // Finally we define the 2d texture
     glTexImage2D(GL_TEXTURE_2D, 0, 4, infoheader.biWidth, infoheader.biHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, l_texture);

     // And create 2d mipmaps for the minifying function
     gluBuild2DMipmaps(GL_TEXTURE_2D, 4, infoheader.biWidth, infoheader.biHeight, GL_RGBA, GL_UNSIGNED_BYTE, l_texture);

     delete [] l_texture; // Free the memory we used to load the texture

     return num_texture; // Returns the current texture OpenGL ID
}

void drawStreetStraight(Vector2d & point1,Vector2d & point2,Vector2d & point3,Vector2d & point4,double length)
{
    glEnable(GL_TEXTURE_2D);
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECR); 
    glBindTexture(GL_TEXTURE_2D,streetTexture);
    glBegin(GL_QUADS);
    glTexCoord2f(0,0);
    glVertex3d(point1.x,0,point1.y);
    glTexCoord2f(1,0);
    glVertex3d(point2.x,0,point2.y);
    glTexCoord2f(1,length/2.0);
    glVertex3d(point3.x,0,point3.y);
    glTexCoord2f(0,length/2.0);
    glVertex3d(point4.x,0,point4.y);
    glEnd();
    glDisable(GL_TEXTURE_2D);
}