Disable color blending between specific objects in Three.js

Question

I'm developing a visualization tool for 2D objects in Three.js.

Like the example shown, I want to take a set of 2D shapes rendered with an orthographic camera and, because each bigger shape "contains" the smaller ones, I've been using the z coordinate to render them in such a way that the bigger objects are rendered behind smaller ones.

That works. However, I want to disable the color blending as if I wasn't drawing full objects everytime but instead drawing its increments/decrements like the example above. Additionally, I want each to blend with the existing contents, like the background or the map shown in the example bellow.

The question is essencially: Is it possible to disable color blending between a set of objects, while allowing color blending between those objects and others (like the background, for example)?

Answer 1

Render them front to back by setting their renderOrder. The depth buffer will then prevent the ones behind drawing where the ones in front have already drawn

#c {
  background-image: url(https://i.imgur.com/zYyAndd.jpg);
  background-size: cover;
}

<canvas id="c"></canvas>
<script type="module">
import * as THREE from 'https://threejsfundamentals.org/threejs/resources/threejs/r113/build/three.module.js';

function main() {
  const canvas = document.querySelector('#c');
  const renderer = new THREE.WebGLRenderer({canvas, alpha:true});

  const fov = 75;
  const aspect = 2;  // the canvas default
  const near = 0.1;
  const far = 5;
  const camera = new THREE.PerspectiveCamera(fov, aspect, near, far);
  camera.position.z = 2;

  const scene = new THREE.Scene();

  const geometry = new THREE.CircleBufferGeometry( .5, 32 );

  for (let i = 0; i < 5; ++i) {
    const material = new THREE.MeshBasicMaterial({
      transparent: true,
      opacity: 0.5,
    });
    material.color.setHSL(i / 5, 1, 0.5);
    const mesh = new THREE.Mesh(geometry, material);
    scene.add(mesh);
    mesh.position.z = i * -0.1;
    const s = 1 + i * 0.5;
    mesh.renderOrder = i;
    mesh.scale.set(s, s, s);
  }

  renderer.render(scene, camera);
}

main();
</script>