Hit test in threejs for skinnedMesh using RTT

hitTest.js

/*
 *
 * Render current frame and check pixel 
 * transparency beneath mouse position.
 * Threejs required.
 *
 */

var gl = renderer.context;
var rtTexture = new THREE.WebGLRenderTarget(WIDTH, HEIGHT, {minFilter: THREE.LinearFilter, magFilter: THREE.NearestFilter, format: THREE.RGBAFormat});
var pixel = new Uint8Array(4);
var framebuffer;

var onMouseDown = function(e) {
    
    // Render to texture
    renderer.render(scene, camera, rtTexture, true);

    // Bind frame buffer to inspect
    framebuffer = rtTexture.__webglFramebuffer;
    gl.bindFramebuffer(gl.FRAMEBUFFER, framebuffer);

    // Inspect pixel at mouse coords, pass results to pixel variable
    gl.viewport(e.clientX, HEIGHT - e.clientY, 1, 1);
    gl.readPixels(e.clientX, HEIGHT - e.clientY, 1, 1, gl.RGBA, gl.UNSIGNED_BYTE, pixel);

    // Unbind frame buffer
    gl.bindFramebuffer(gl.FRAMEBUFFER, null);

    console.log(pixel); // rgba values
    console.log(!!pixel[3]); // True if not transparent
};