private void SetModelTransparency(double transparency)
        {
            foreach (var modelItem in DrawingControl.Viewport.Children.OfType<ModelVisual3D>())
            {
                SetTransparency(modelItem.Content, transparency);
            }
        }

        private void SetTransparency(Model3D model, double transparency)
        {
            if (model is GeometryModel3D geometryModel)
            {
                var newMaterialGroup = new MaterialGroup();
                ApplyTransparencyToMaterial(geometryModel.Material, transparency, newMaterialGroup);
                geometryModel.Material = newMaterialGroup;
            }
            else if (model is Model3DGroup modelGroup)
            {
                foreach (var child in modelGroup.Children)
                {
                    SetTransparency(child, transparency);
                }
            }
        }

        private void ApplyTransparencyToMaterial(Material material, double transparency, MaterialGroup newMaterialGroup)
        {
            if (material is MaterialGroup materialGroup)
            {
                foreach (var subMaterial in materialGroup.Children)
                {
                    ApplyTransparencyToMaterial(subMaterial, transparency, newMaterialGroup);
                }
            }
            else if (material is DiffuseMaterial diffuseMaterial)
            {
                var color = ((SolidColorBrush)diffuseMaterial.Brush).Color;
                color.A = (byte)(transparency * 255);
                /*diffuseMaterial.Brush = new SolidColorBrush(color)
                {
                    Opacity = transparency
                };*/
                var newDiffuseMaterial = new DiffuseMaterial(new SolidColorBrush(color));
                newMaterialGroup.Children.Add(newDiffuseMaterial);
            }
            else
            {
                newMaterialGroup.Children.Add(material.Clone());
            }
        }

I use XbimWindowsUI library to render the IFC file. The above code transparents the x,y grid lines but not transparenting the models. I tried with DrawingControl.Opacity = e.NewValue(); but it’s also not working. Is there a way to work around?