constructor( scene, camera, clearColor, clearAlpha ) {

			super();
			this.scene = scene;
			this.camera = camera;
			this.sampleLevel = 4; // specified as n, where the number of samples is 2^n, so sampleLevel = 4, is 2^4 samples, 16.

			this.unbiased = true; // as we need to clear the buffer in this pass, clearColor must be set to something, defaults to black.

			this.clearColor = clearColor !== undefined ? clearColor : 0x000000;
			this.clearAlpha = clearAlpha !== undefined ? clearAlpha : 0;
			this._oldClearColor = new THREE.Color();
			if ( THREE.CopyShader === undefined ) console.error( 'THREE.SSAARenderPass relies on THREE.CopyShader' );
			const copyShader = THREE.CopyShader;
			this.copyUniforms = THREE.UniformsUtils.clone( copyShader.uniforms );
			this.copyMaterial = new THREE.ShaderMaterial( {
				uniforms: this.copyUniforms,
				vertexShader: copyShader.vertexShader,
				fragmentShader: copyShader.fragmentShader,
				premultipliedAlpha: true,
				transparent: true,
				blending: THREE.AdditiveBlending,
				depthTest: false,
				depthWrite: false
			} );
			this.fsQuad = new THREE.FullScreenQuad( this.copyMaterial );

		}
Supersample Anti-Aliasing Render THREE.Pass

This manual approach to SSAA re-renders the scene ones for each sample with camera jitter and accumulates the results.

References: https://en.wikipedia.org/wiki/Supersampling