Set transparent for specific element - autodesk-forge

Question

I want set transparent for specific element, i follow this code:
var instanceTree = this.viewer.model.getInstanceTree();
var fragList = this.viewer.model.getFragmentList();
this.listElement.forEach(element => {
instanceTree.enumNodeFragments(element, (fragId) => {
console.log(element.material)
var material = fragList.getMaterial(fragId)
if (material) {
material.opacity = value;
material.transparent = true;
material.needsUpdate = true;
}
});
});
this.viewer.impl.invalidate(true, true, true);
but it overide for all elements have that material. How can i set for selected element?
Appreciate any comments.
UPDATE 1:
i found go around way is clone main material than register it with different name:
var newMaterial = material.clone();
const materials = this.viewer.impl.matman();
materials.addMaterial('mymaterial',newMaterial,true);
fragList.setMaterial(fragId,newMaterial);
newMaterial.opacity = value;
newMaterial.transparent = true;
newMaterial.needsUpdate = true;
but effect is not what i want, it has different color and when set transparent i can only see a couple object behind it

Answer 1

You can create your own, custom THREE.js material and assign it to the fragment using fragList.setMaterial(fragId, material).
For more information on using custom materials or shaders, see https://forge.autodesk.com/blog/custom-shader-materials-forge-viewer.
EDIT:
Regarding the visual anomalies (for example, when you only see some of the objects behind something semi-transparent), this is a known problem, unfortunately with no clear solution. When the Forge Model Derivative service creates an SVF file to be viewed in Forge Viewer, the individual scene elements are stored in a data structure optimized for fast traversal, depending on whether they are semi-transparent or fully opaque. This data structure is fixed, and so unfortunately, when you take an object that was originally fully opaque, and you make it semi-transparent, it will most likely be rendered in a wrong order...