OpenGL保存bmp图片(字节对齐与RGB分量转换)

http://blog.sina.com.cn/s/blog_60707c0f0100q9vf.html

现在的OpenGL己经具有GL_BGR_EXT的方式读取像素，默认己经是4字节对齐了，所以下面代码注释掉了处理部分，如果你的OpenGL不支持，GL_BGR_EXT,把注释部分复原即可。

 BOOL SaveBMPFromOpenGl(LPCTSTR lpFileName)
 {
   ASSERT(lpFileName != NULL);
   GLint viewport[4];
   glGetIntegerv(GL_VIEWPORT, viewport);
   CRect rect;
   GetClientRect(rect);
   int width = viewport[2];
   int height = viewport[3];
    //glPixelStorei(GL_UNPACK_ALIGNMENT, 4);
   int nAlignWidth = (width*24+31)/32;
   unsigned char* pdata = new unsigned char[nAlignWidth * height * 4];
   memset(pdata, 0, nAlignWidth * height * 4);
   glReadPixels(0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE, pdata);
   ////由RGB变BGR
   //for(int i = 0 ; i < width * height * 3 ; i += 3)
   //{
   // unsigned char tmpRGB;
   // tmpRGB     = pdata[i];
   // pdata[i]   = pdata[i+2];
   // pdata[i+2] = tmpRGB;
   //}
   ////四字节对齐
   //int nAlignWidth = (width*24+31)/32;
   //unsigned char *pDataAfterAlign = (unsigned char *) malloc(4 * nAlignWidth * height);
   //memset(pDataAfterAlign, 0, 4 * nAlignWidth * height);
   //int nZero = 4*nAlignWidth - 3*width;
   //for(int j=0; j<height; j++)
   //{
   //  for(int i=0; i<width*3; i++)
   //  {
   //     pDataAfterAlign[j*(nZero+3*width)+i] = pdata[3*width*j+i];
   //  }
   //}
   BITMAPFILEHEADER Header;
   BITMAPINFOHEADER HeaderInfo;
   Header.bfType = 0x4D42;
   Header.bfReserved1 = 0;
   Header.bfReserved2 = 0;
   Header.bfOffBits = (DWORD)(sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER)) ;
   Header.bfSize =(DWORD)(sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + nAlignWidth* height * 4);
   HeaderInfo.biSize = sizeof(BITMAPINFOHEADER);
   HeaderInfo.biWidth = width;
   HeaderInfo.biHeight = height;
   HeaderInfo.biPlanes = 1;
   HeaderInfo.biBitCount = 24;
   HeaderInfo.biCompression = 0;
   HeaderInfo.biSizeImage = 4 * nAlignWidth * height;
   HeaderInfo.biXPelsPerMeter = 0;
   HeaderInfo.biYPelsPerMeter = 0;
   HeaderInfo.biClrUsed = 0;
   HeaderInfo.biClrImportant = 0;
   FILE *pfile;
   if(!(pfile = fopen(lpFileName, "wb+")))
   {
     AfxMessageBox("保存图像失败!");
     return FALSE;
   }
   fwrite(&Header, 1, sizeof(BITMAPFILEHEADER), pfile);
   fwrite(&HeaderInfo, 1, sizeof(BITMAPINFOHEADER), pfile);
   fwrite(pdata, 1, HeaderInfo.biSizeImage, pfile);
   fclose(pfile);
   delete[] pdata;
   return TRUE;
 }

O了，主要功能就是一个函数:

void glReadPixels( GLint x, 
GLint y, 
GLsizei width, 
GLsizei height, 
GLenum format, 
GLenum type, 
GLvoid * data);