Three.js usage with stencil buffer - three.js

Question

I can't get the following to draw the scene into the shape created as a stencil mask. Instead the code just seems to render the stencil itself as a black object.
http://signaturefloors.dev.flooradvisor.com.au/productapp/floor_align.php
My render function is:
var gl = floor_align.renderer.domElement.getContext('webgl') || floor_align.renderer.domElement.getContext('experimental-webgl');
gl.clearStencil(0);
gl.clear(gl.STENCIL_BUFFER_BIT);
gl.enable(gl.STENCIL_TEST);
gl.stencilFunc(gl.ALWAYS, 1, 1);
gl.stencilOp(gl.KEEP, gl.REPLACE, gl.REPLACE);
gl.colorMask(0, 0, 0, 0);
// Floor Mask (Create a stencil that we render the next pass into)
floor_align.renderer.render(floor_align.maskScene, floor_align.maskCamera);
gl.colorMask(1, 1, 1, 1);
gl.stencilFunc(gl.NOTEQUAL, 1, 1);
gl.stencilOp(gl.KEEP, gl.REPLACE, gl.REPLACE);
// Render a floor pass
floor_align.renderer.render(floor_align.scene, floor_align.camera);
gl.disable(gl.STENCIL_TEST);
The renderer has autoClear = false;

Answer 1

Accepted answer don't work on latest threejs. If anyone interested, here's an up-to-date version that works (using r111):
gl.enable(gl.STENCIL_TEST);
gl.stencilOp(gl.KEEP, gl.KEEP, gl.REPLACE);
//renderer.clear(); <-- works without this too
gl.stencilFunc(gl.ALWAYS, 1, 0xFF);
gl.stencilMask(0xFF);
renderer.render(maskScene, camera);
gl.stencilFunc(gl.EQUAL, 1, 0xFF);
gl.stencilMask(0x00);
renderer.render(scene, camera);
gl.stencilMask(0xFF);
gl.disable(gl.STENCIL_TEST);
Also in my case I didn't disable auto-clear and it still works.

Answer 2

Through trial and error I updated my code to this and it now works. Clearing the depth buffer seems particularly important so I guess my mask must have been hiding the more distant floor fragments.
// Render the scene
function fla_render() {
floor_align.renderer.clear();
// Background
//floor_align.renderer.render(floor_align.scene, floor_align.camera);
floor_align.renderer.clearDepth();
var gl = floor_align.renderer.domElement.getContext('webgl') || floor_align.renderer.domElement.getContext('experimental-webgl');
// Clear the stencil buffer
gl.clearStencil(0);
gl.clear(gl.STENCIL_BUFFER_BIT);
// Replacing the values at the stencil buffer to 1 on every pixel we draw
gl.stencilFunc(gl.ALWAYS, 1, 1);
gl.stencilOp(gl.KEEP, gl.REPLACE, gl.REPLACE);
// Disable color (u can also disable here the depth buffers)
gl.colorMask(false, false, false, false);
// Write to stencil
gl.enable(gl.STENCIL_TEST);
// Floor Mask (Create a stencil that we render the next pass into)
floor_align.renderer.render(floor_align.maskScene, floor_align.maskCamera);
// Telling the stencil now to draw/keep only pixels that equals 1 - which we set earlier
gl.stencilFunc(gl.EQUAL, 1, 1);
gl.stencilOp(gl.KEEP, gl.KEEP, gl.KEEP);
// Clear depth buffer (seems important)
floor_align.renderer.clearDepth();
// Enable color
gl.colorMask(true, true, true, true);
// Render a floor pass
floor_align.renderer.render(floor_align.scene, floor_align.camera);
// Disable stencil test;
gl.disable(gl.STENCIL_TEST);
}