Как установить прозрачность альфа-канала p5.js в шейдере?

let shdr;

function setup() {
  createCanvas(windowWidth, windowHeight, WEBGL);
  shdr = createShader(vert, frag);
  noStroke();
}

function draw() {  
  background(255);
  
  orbitControl(2, 1, 0.1);
  
  shader(shdr);
  shdr.setUniform("uColor", [1, 0, 0]);
  push();
  translate(-100, 0, 0)
  cylinder(30, 50);
  pop();
  
  shdr.setUniform("uColor", [0, 0, 1]);
  push()
  translate(100, 0, 0)
  cylinder(30, 50);
  pop()
}

const vert = `
// Transformation matrices
uniform mat4 uModelViewMatrix;
uniform mat4 uProjectionMatrix;

attribute vec3 aPosition;
// P5 provides us with texture coordinates for most shapes
attribute vec2 aTexCoord;

// This is a varying variable, which in shader terms means that it will be passed from the vertex shader to the fragment shader
varying vec2 vTexCoord;

void main() {
  // Copy the texcoord attributes into the varying variable
  vTexCoord = aTexCoord;
  
        
  vec4 viewModelPosition = uModelViewMatrix * vec4(aPosition, 1.0);
  gl_Position = uProjectionMatrix * viewModelPosition;
}
`;

const frag = `
precision mediump float;

uniform vec3 uColor;


void main()
{
  gl_FragColor = vec4(uColor, 0.33);
}
`;

html, body {
  margin: 0;
  padding: 0;
  overflow: hidden;
}

<script src = "https://cdnjs.cloudflare.com/ajax/libs/p5.js/1.9.0/p5.js"></script>