Multiple transparent textures on the same mesh face in Three.js

Use ShaderMaterial and set both textures as uniforms, and then blend them within shader.

I made this example: http://abstract-algorithm.com/three_sh/ and that really should be enough.

So, you make ShaderMaterial:

var vertShader = document.getElementById('vertex_shh').innerHTML;
var fragShader = document.getElementById('fragment_shh').innerHTML;

var attributes = {}; // custom attributes

var uniforms = {    // custom uniforms (your textures)

  tOne: { type: "t", value: THREE.ImageUtils.loadTexture( "cover.png" ) },
  tSec: { type: "t", value: THREE.ImageUtils.loadTexture( "grass.jpg" ) }

};

var material_shh = new THREE.ShaderMaterial({

  uniforms: uniforms,
  attributes: attributes,
  vertexShader: vertShader,
  fragmentShader: fragShader

});

And create mesh with that material:

var me = new THREE.Mesh( new THREE.CubeGeometry(80,80,80), material_shh );

You can put simplest vertex shader:

varying vec2 vUv;

void main()
{
    vUv = uv;
    vec4 mvPosition = modelViewMatrix * vec4( position, 1.0 );
    gl_Position = projectionMatrix * mvPosition;
}

And fragment shader that will actually do the blending:

#ifdef GL_ES
precision highp float;
#endif

uniform sampler2D tOne;
uniform sampler2D tSec;

varying vec2 vUv;

void main(void)
{
    vec3 c;
    vec4 Ca = texture2D(tOne, vUv);
    vec4 Cb = texture2D(tSec, vUv);
    c = Ca.rgb * Ca.a + Cb.rgb * Cb.a * (1.0 - Ca.a);  // blending equation
    gl_FragColor= vec4(c, 1.0);
}

If you need to blend even more textures, you use same equation for blending just multiple times.

So here’s the result: