PostProcessStageComposite

// Example 1: separable blur filter
// The input to blurXDirection is the texture rendered to by the scene or the output of the previous stage.
// The input to blurYDirection is the texture rendered to by blurXDirection.
scene.postProcessStages.add(new PostProcessStageComposite({
    stages : [blurXDirection, blurYDirection]
}));

// Example 2: referencing the output of another post-process stage
scene.postProcessStages.add(new PostProcessStageComposite({
    inputPreviousStageTexture : false,
    stages : [
        // The same as Example 1.
        new PostProcessStageComposite({
            inputPreviousStageTexture : true
            stages : [blurXDirection, blurYDirection],
            name : 'blur'
        }),
        // The input texture for this stage is the same input texture to blurXDirection since inputPreviousStageTexture is false
        new PostProcessStage({
            fragmentShader : compositeShader,
            uniforms : {
                blurTexture : 'blur' // The output of the composite with name 'blur' (the texture that blurYDirection rendered to).
            }
        })
    ]
});

// Example 3: create a uniform alias
const uniforms = {};
defineProperties(uniforms, {
    filterSize : {
        get : function() {
            return blurXDirection.uniforms.filterSize;
        },
        set : function(value) {
            blurXDirection.uniforms.filterSize = blurYDirection.uniforms.filterSize = value;
        }
    }
});
scene.postProcessStages.add(new PostProcessStageComposite({
    stages : [blurXDirection, blurYDirection],
    uniforms : uniforms
}));