glVertex3f缩放问题

OpenGL的新手，请放心。我的任务是在我的学校项目中使用GLFont来渲染文本，我在下面粘贴了它的渲染方法。我已经使用glOrtho将原点设置为窗口的左上角，但这会导致GLFont倒置呈现字符的问题。我需要做的是按-1缩放y，但我不知道如何更改下面的渲染器。有什么想法吗？

void GLFont::RenderText (const char* String, float x, float y, float z, float size)
{
    //Return if we don't have a valid glFont
    if (!ok)
    {
        throw GLFontError::InvalidFont();
    }
    //Get length of string
    int Length = strlen(String);
    //Begin rendering quads
    glBegin(GL_TRIANGLE_STRIP);
    //Loop through characters
    for (int i = 0; i < Length; i++)
    {
        //Get pointer to glFont character
        GLFONTCHAR *Char = &Font.Char[(int)String[i] - Font.IntStart];
        float dx = Char->dx*size;
        float dy = Char->dy*size;
        //Specify vertices and texture coordinates
        glTexCoord2f(Char->tx1, Char->ty2);
        glVertex3f(x, y - dy, z);
        glTexCoord2f(Char->tx1, Char->ty1);
        glVertex3f(x, y, z);
        glTexCoord2f(Char->tx2, Char->ty2);
        glVertex3f(x + dx, y - dy, z);
        glTexCoord2f(Char->tx2, Char->ty1);
        glVertex3f(x + dx, y, z);
        //Move to next character
        x += dx;
    }
    //Stop rendering quads
    glEnd();
}