PFNGLMATRIXORTHOEXTPROCDart typedef
        PFNGLMATRIXORTHOEXTPROCDart =
     void Function(int mode, double left, double right, double bottom, double top, double zNear, double zFar)
    
    
    
Implementation
typedef PFNGLMATRIXORTHOEXTPROCDart =
    void Function(
      int mode,
      double left,
      double right,
      double bottom,
      double top,
      double zNear,
      double zFar,
    );