Setting Material.blending to "CustomBlending" no longer works blends as expected

Describe the bug

As of r137 using “CustomBlending” does not work as expected.

To Reproduce

Create a material that uses “CustomBlending” and a partial opacity. In r136 it is rendered as partially transparent while in r137 it is not.

Code

const material = new THREE.MeshBasicMaterial( {
  blending: CustomBlending,
  opacity: 0.5
} );

Live example

• https://jsfiddle.net/c9v0jdrL/

Expected behavior

When using custom blending it renders as partially transparent as it did in r136.

Screenshots

From the js fiddle above. Left is a regular transparent cube. Right is using CustomBlending.

r136	r137

Platform:

• Device: Desktop
• OS: MacOS
• Browser: Chrome
• Three.js version: r137.5

[mrdoob]

Basically, apparently many systems do not create a webgl context with alpha: false so the browser has to emulate it.

My main laptop (Intel MacBook Pro 2016) is one of the worst cases apparently, so I’ve been dealing with subpar performance and noisy fans for years… Now it feels like a brand new laptop 😬

[WestLangley]

Hmmm… I would have expected the default values for CustomBlending match the values that produce NormalBlending. At least doing so would have been a reasonable default.

It did previously…

Well, if that were the case, then you would have had no reason to use the default CustomBlending because it would have been the same as NormalBlending. Right?