Complex shape character outline

Question

Say I have this character and I want allow user to select it, so when it s selected I want to show an outline around it.

the character is an object3D with some meshes. I tried to clone and set a backside material, but it did NOT work, the problem was each cube in the shape was render with backside separately so the outline was wrong.

do I need to create another mesh for the outline, is there an easier way?

Answer 1

What @spassvolgel wrote is correct;

What I suspect needs to be done is something like this: 1. First the background needs to be rendered 2. Then, on a separate transparent layer, the character model with a flat color, slightly bigger than the original, 3. On another transparent layer the character with its normal material / texture 4. Finally, the character layer needs to go on top of the outline layer and them combined need to be placed in the bg

You just create multiple scenes and combine them with sequential render passes:

renderer.autoClear = false;
. . . 

renderer.render(scene, camera); // the entire scene
renderer.clearDepth();
renderer.render(scene2, camera); // just the selected item, larger, in a flat color
renderer.render(scene3, camera); // the selected item again

three.js.r.129