OpenGL按照窗口宽高比进行图片放大缩小

把图像尽量拉满：

void ext(int & w, int &h, int winW, int WinH)
{
     double  wRatio = winW * 1.0f / w;
     double  hRatio = WinH * 1.0f / h;
    if (wRatio < hRatio) {
        w = winW;
        h = (int) (wRatio * h);
    } else {
        h= WinH;
        w = (int) (hRatio * w);
    }
}