Three.js usage with stencil buffer

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.

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Answer 1

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);

}

Answer 2

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.