Three.js / WebGL - transparent planes hiding other planes behind them

When you have two planes in Three.js / WebGL and one or both of them are transparent, sometimes the plane behind will be hidden by the transparent plane above. Why is this?

Solution 1:

Let's say that you are using some transparent *.png image. Then this would help:

new THREE.MeshBasicMaterial( { side:THREE.BackSide,map:texture, depthWrite: false, depthTest: false });

Solution 2:

Setting the depthWrite property to false solved my issue.

new THREE.MeshBasicMaterial({ 
    opacity: 0.25, 
    transparent: true, 
    side: THREE.DoubleSide, 
    depthWrite: false
});

Solution 3:

Try adding alphaTest: 0.5 to the material.

Solution 4:

This is not a bug, it's just how OpenGL (and, hence, WebGL) works. Transparent surfaces don't play well with the z-buffer, and as such must be manually sorted and rendered back-to-front. Three JS is attempting to do this for you (which is why the problem goes away when you set the X value > 0) but cannot robustly handle the case of intersecting geometry like you're showing.

I've explained the issue more in-depth in a different SO question, so you may want to reference that.