anchor.diff:    var tmpl = rayMarchingFrag0;
     var stepmax = 256;
     var epsilon_de = 0.005;
  +  var debugPrintFragShader = false;
   
     final _os = new List<ObjectInfo>();
     var _needShaderUpdate = true;
  
positive.code:   String de;
    /// code of the signed distance of the object (shape)
    String sd;
    /// shade fragment to insert into the shade
    String sh;
    /// code of the material of the object
  
negative.code:       ctx.gl.uniform3fv(ctx.getUniformLocation(glf.SFNAME_FOCUSPOSITION), camera.focusPosition.storage);
        _os.forEach((x){if (x.at != null) { x.at(ctx); }});
      });
      _needShaderUpdate = false;
    }
  
  