Make 3D model transparent by setting alpha values, change blending mode at runtime.

[MukeshBlippar]

Hi, I'm using your library and it's wonderful. I have requirement to set Fade in / out animation on 3D models. And also to change the opacity of any model at run time to make it transparent. So far from all the issues in sceneform and filament, I learnt that it's only possible if the blending mode of model is set 'Transparent' or 'Fade'. But the default blending mode is 'Opaque' which is not allowing to set the alpha values. And Filament API also doesn't allow to change the blending mode at run time.
I managed to set opacity for the model by creating my own custom material and applying the on renderable. But this over rides the existing material. So the question is how can we achieve to set the alpha value in existing material. Any plan to add this feature in future? Here is my code which is working to create material with alpha value.

 Material materialFilament;
 MaterialBuilder.init();
        MaterialBuilder materialBuilder = new MaterialBuilder()
                .platform(MaterialBuilder.Platform.MOBILE)
                .name("External Glb Material")
                .require(MaterialBuilder.VertexAttribute.UV0)
                .shading(MaterialBuilder.Shading.UNLIT)
                .doubleSided(false)
                .optimization(MaterialBuilder.Optimization.NONE);

        MaterialPackage materialPackage = materialBuilder
                .blending(MaterialBuilder.BlendingMode.TRANSPARENT)
                .material("void material(inout MaterialInputs material) {\n" +
                        "    prepareMaterial(material);\n" +
                        "    material.baseColor.a = 0.30;\n" +
                        "    material.baseColor.rgb *= material.baseColor.a;\n" +
                        "}\n")
                .build(filamentEngine);

        if (materialPackage.isValid()) {
            ByteBuffer buffer = materialPackage.getBuffer();
            materialFilament = new com.google.android.filament.Material.Builder()
                    .payload(buffer, buffer.remaining())
                    .build(filamentEngine);
        }
        MaterialBuilder.shutdown();

[ThomasGorisse]

Hi.
In your case, I would strongly advice having your model directly comming from a gltf (You can easily create your shapes using Blender and export as glTF).
Once your model is loaded, you will just have to change it material parameters without having to apply a new one from scratch:

node.modelInstance?.materialInstance?.setParameter(
          "baseColorFactor",
          // Red
          0.09f,
          // Green
          0.44f,
          // Blue
          0.95f,
          // Alpha
          0.75f
      )

[MukeshBlippar]

Hi @ThomasGorisse Thanks for your quick reply. Above solution is only working if the blending mode of the model is already set 'transparent/alpha blend'. Is there any way to change the blending mode using scene form/filament on runtime inside the app. Our models have opaque blending by default.

[ThomasGorisse]

You should ask it on the Filament repository

[MukeshBlippar]

Yes, I will ask there also. I was just wondering if there is some plan to add such feature at scene from api level. That's why I added in discussion here. Would be great if fadein/out animation you can add.

[ThomasGorisse]

And change your model Blend Mode to Alpha Blend if you want it to handle transparency.