anchor.diff:      _dt  = 0.0;
     }
   }
  +
  +var mdt = new glf.MeshDefTools();
   
   class Main {
   
  
positive.code:     var md = null;
      switch(_selectMeshUI.value) {
        case 'box24' :
          md = glf.makeMeshDef_box24Vertices(dx: 2.0, dy: 1.0, dz: 0.5, ty: 1.0);
          break;
        case 'box24-t' :
          md = glf.makeMeshDef_box24Vertices(dx: 2.0, dy: 1.0, dz: 0.5, tx: 2.0, ty: 1.0, tz: 0.5);
          break;
        case 'cube8' :
          md = glf.makeMeshDef_box8Vertices(dx: 0.5, dy: 0.5, dz: 0.5);
          break;
        case 'sphereL':
          md = glf.makeMeshDef_sphere(subdivisionsAxis : sub, subdivisionsHeight : sub);
          break;
        default:
          md = glf.makeMeshDef_box24Vertices(dx: 0.5, dy: 0.5, dz: 0.5);
      }
      if (_showWireframeUI.checked) {
        md.lines = glf.extractWireframe(md.triangles);
        md.triangles = null;
      }
      return md;
  
negative.code: 
  
    _add(renderer, ctx) {
      geometry.meshDef = mdt.makePlane(dx: 3.0, dy: 3.0);
      glf.makeNormalMatrix(geometry.transforms, geometry.normalMatrix);
      var material = new Material()
      //..transparent = true
      ..ctx = ctx
      ..cfg = (ctx) {
        ctx.gl.uniform3f(ctx.getUniformLocation(glf.SFNAME_COLORS), 0.0, 0.5, 0.5);
  