Fade to transparency from a point (center).

export function modAppendFade(shader, background) {
  // assumes: https://github.com/mrdoob/three.js/blob/dev/src/renderers/shaders/ShaderLib/meshbasic.glsl.js
  shader.vertexShader = shader.vertexShader.replace(
    /* glsl */`void main() {`,
    /* glsl */`
      varying vec4 v_position;
      void main() {
        v_position = modelMatrix * vec4(position.xyz, 1.0);
    `
  )
  shader.fragmentShader = /* glsl */`
    varying vec4 v_position;
    ${shader.fragmentShader}
  `.replace(
    /* glsl */`#include <dithering_fragment>`,
    /* glsl */`
        #include <dithering_fragment>

        vec3 center = vec3(0.0, 0.0, 0.0);
        vec4 background = vec4(${background || '0.93, 0.93, 0.93, 1.0'});
        float diameter = 800.0;
        float falloff = 0.006;

        float vDistance = distance(v_position.xyz, center);
        float factor = clamp((vDistance - diameter) * falloff, 0.0, 1.0);
        gl_FragColor = mix(gl_FragColor, background, factor);
      `
  )
}

node.material.onBeforeCompile = shader => modAppendFade(shader)
node.material.transparent = true
node.material.needsUpdate = true