Regl color and alpha blending of primitives

Question

I am trying to figure out how to achieve color and alpha blending between primitives using Regl.

I know Regl command's have a blend property and I've tried replicating the following webgl settings that do the trick:

gl.enable(gl.BLEND);
gl.blendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA);

using the following blend settings in Regl:

blend: {
  enable: true,
  func: { src: 'src alpha', dst:'one minus src alpha' }
},

But the blending only seem to work in regard to the background color but not between the points. (See the example below.)

Example: http://jsfiddle.net/8gyf7pek/13/

const canvas1 = document.querySelector('#c1');
const canvas2 = document.querySelector('#c2');

//////////////////////////////////////////////
// PURE WEBGL
//////////////////////////////////////////////

const gl = canvas1.getContext('webgl');
gl.enable(gl.BLEND);
gl.blendFunc(gl.SRC_ALPHA, gl.ONE_MINUS_SRC_ALPHA);
const vertexShaderSource = `
  attribute vec2 position;
  attribute vec4 color;
  varying vec4 v_color;

  void main() {
    gl_PointSize = 50.0;
    gl_Position = vec4(position, 0, 1);
    v_color = color;
  }
`;

const fragmentShaderSource = `
  precision mediump float;
  varying vec4 v_color;
  void main() {
    gl_FragColor = v_color;
  }
`;

const vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource);
const fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource);
const program = createProgram(gl, vertexShader, fragmentShader);
gl.useProgram(program);

const positionAttributeLocation = gl.getAttribLocation(program, 'position');
const colorAttributeLocation = gl.getAttribLocation(program, 'color');
const positionBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
gl.enableVertexAttribArray(positionAttributeLocation);
gl.vertexAttribPointer(positionAttributeLocation, 2, gl.FLOAT, false, 0, 0);

const colorBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, colorBuffer);
gl.enableVertexAttribArray(colorAttributeLocation);
gl.vertexAttribPointer(colorAttributeLocation, 4, gl.FLOAT, false, 0, 0);

gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
  -0.05, -0.05, -0.05, 0.05, 0.05, 0.05, 0.05, -0.05,
]), gl.STATIC_DRAW);
gl.bindBuffer(gl.ARRAY_BUFFER, colorBuffer);
const red = [1, 0, 0, 0.5];
const blue = [0, 0, 1, 0.5];
gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([
  ...red, ...red,
  ...blue, ...blue,
]), gl.STATIC_DRAW);

gl.drawArrays(gl.POINTS, 0, 4);

function createShader(gl, type, shaderSource) {
  const shader = gl.createShader(type);
  gl.shaderSource(shader, shaderSource);
  gl.compileShader(shader);
  const success = gl.getShaderParameter(shader, gl.COMPILE_STATUS);
  if(!success) {
    console.warn(gl.getShaderInfoLog(shader));
    gl.deleteShader(shader);
  }
  return shader;
}

function createProgram(gl, vertexShader, fragmentShader) {
  const program = gl.createProgram();
  gl.attachShader(program, vertexShader);
  gl.attachShader(program, fragmentShader);
  gl.linkProgram(program);
  const success = gl.getProgramParameter(program, gl.LINK_STATUS);
  if(!success) {
    console.log(gl.getProgramInfoLog(program));
    gl.deleteProgram(program);
  }
  return program;
}

//////////////////////////////////////////////
// REGL
//////////////////////////////////////////////

const regl = createREGL(canvas2);

regl.clear({ color: [0, 0, 0, 0], depth: 1 });

regl({
  frag: `
  precision mediump float;
  varying vec4 fragColor;
  void main () {
    gl_FragColor = fragColor;
  }`,

  vert: `
  precision mediump float;
  attribute vec2 position;
  attribute vec4 color;
  varying vec4 fragColor;
  uniform float pointWidth;
  void main () {
    fragColor = color;
 gl_PointSize = pointWidth;
    gl_Position = vec4(position, 0, 1);
  }`,

  attributes: {
    position: [
      [-0.05, -0.05],
      [-0.05, 0.05],
      [0.05, -0.05],
      [0.05, 0.05],
    ],
    color: [
      [1, 0, 0, 0.5],
      [1, 0, 0, 0.5],
      [0, 0, 1, 0.5],
      [0, 0, 1, 0.5]
    ],
  },

  uniforms: {
    pointWidth: 50,
  },
  
  blend: {
   enable: true,
    func: { src: 'src alpha', dst:'one minus src alpha' }
  },

  count: 4,
  
  primitive: 'points',
})();

#bg {
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  color: #808080;
  background: black;
}
#c1, #c2 {
  width: 240px;
  height: 240px;
  border: 1px solid white;
}
em {
  display: block;
}

<div id="bg">
  <canvas id="c1"></canvas>
  <canvas id="c2"></canvas>
  <em>Left is pure WebGL. Right is Regl.</em>
</div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/regl/1.3.7/regl.min.js"></script>

Am I doing something wrong? How could I achieve the same kind of blending that the pure webgl code produces? Thanks!

Answer 1

Thanks to this great answer I figured it out:

In a nutshell, the blend function needs to be adjusted and the depth test needs to be disabled. (But I still don't know why the blend function, that worked in the vanilla WebGL example, didn't work in Regl)

1. Use the following blend mode

   blend: {
     enable: true,
     func: {
       srcRGB: 'src alpha',
       srcAlpha: 'src alpha',
       dstRGB: 'one minus src alpha',
       dstAlpha: 'one minus src alpha',
     },
   },
   

2. Disable depth test

   depth: { enable: false },
   

Here's the fixed example from my question: http://jsfiddle.net/8gyf7pek/22/