three.js/examples/js/postprocessing/SSAARenderPass.js

( function () {

	/**
*
* 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
*
*/

	var SSAARenderPass = function ( scene, camera, clearColor, clearAlpha ) {

		THREE.Pass.call( this );
		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' );
		var 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.Pass.FullScreenQuad( this.copyMaterial );

	};

	SSAARenderPass.prototype = Object.assign( Object.create( THREE.Pass.prototype ), {
		constructor: SSAARenderPass,
		dispose: function () {

			if ( this.sampleRenderTarget ) {

				this.sampleRenderTarget.dispose();
				this.sampleRenderTarget = null;

			}

		},
		setSize: function ( width, height ) {

			if ( this.sampleRenderTarget ) this.sampleRenderTarget.setSize( width, height );

		},
		render: function ( renderer, writeBuffer, readBuffer ) {

			if ( ! this.sampleRenderTarget ) {

				this.sampleRenderTarget = new THREE.WebGLRenderTarget( readBuffer.width, readBuffer.height, {
					minFilter: THREE.LinearFilter,
					magFilter: THREE.LinearFilter,
					format: THREE.RGBAFormat
				} );
				this.sampleRenderTarget.texture.name = 'SSAARenderPass.sample';

			}

			var jitterOffsets = SSAARenderPass.JitterVectors[ Math.max( 0, Math.min( this.sampleLevel, 5 ) ) ];
			var autoClear = renderer.autoClear;
			renderer.autoClear = false;
			renderer.getClearColor( this._oldClearColor );
			var oldClearAlpha = renderer.getClearAlpha();
			var baseSampleWeight = 1.0 / jitterOffsets.length;
			var roundingRange = 1 / 32;
			this.copyUniforms[ 'tDiffuse' ].value = this.sampleRenderTarget.texture;
			var width = readBuffer.width,
				height = readBuffer.height; // render the scene multiple times, each slightly jitter offset from the last and accumulate the results.

			for ( var i = 0; i < jitterOffsets.length; i ++ ) {

				var jitterOffset = jitterOffsets[ i ];

				if ( this.camera.setViewOffset ) {

					this.camera.setViewOffset( width, height, jitterOffset[ 0 ] * 0.0625, jitterOffset[ 1 ] * 0.0625, // 0.0625 = 1 / 16
						width, height );

				}

				var sampleWeight = baseSampleWeight;

				if ( this.unbiased ) {

					// the theory is that equal weights for each sample lead to an accumulation of rounding errors.
					// The following equation varies the sampleWeight per sample so that it is uniformly distributed
					// across a range of values whose rounding errors cancel each other out.
					var uniformCenteredDistribution = - 0.5 + ( i + 0.5 ) / jitterOffsets.length;
					sampleWeight += roundingRange * uniformCenteredDistribution;

				}

				this.copyUniforms[ 'opacity' ].value = sampleWeight;
				renderer.setClearColor( this.clearColor, this.clearAlpha );
				renderer.setRenderTarget( this.sampleRenderTarget );
				renderer.clear();
				renderer.render( this.scene, this.camera );
				renderer.setRenderTarget( this.renderToScreen ? null : writeBuffer );

				if ( i === 0 ) {

					renderer.setClearColor( 0x000000, 0.0 );
					renderer.clear();

				}

				this.fsQuad.render( renderer );

			}

			if ( this.camera.clearViewOffset ) this.camera.clearViewOffset();
			renderer.autoClear = autoClear;
			renderer.setClearColor( this._oldClearColor, oldClearAlpha );

		}
	} ); // These jitter vectors are specified in integers because it is easier.
	// I am assuming a [-8,8) integer grid, but it needs to be mapped onto [-0.5,0.5)
	// before being used, thus these integers need to be scaled by 1/16.
	//
	// Sample patterns reference: https://msdn.microsoft.com/en-us/library/windows/desktop/ff476218%28v=vs.85%29.aspx?f=255&MSPPError=-2147217396

	SSAARenderPass.JitterVectors = [[[ 0, 0 ]], [[ 4, 4 ], [ - 4, - 4 ]], [[ - 2, - 6 ], [ 6, - 2 ], [ - 6, 2 ], [ 2, 6 ]], [[ 1, - 3 ], [ - 1, 3 ], [ 5, 1 ], [ - 3, - 5 ], [ - 5, 5 ], [ - 7, - 1 ], [ 3, 7 ], [ 7, - 7 ]], [[ 1, 1 ], [ - 1, - 3 ], [ - 3, 2 ], [ 4, - 1 ], [ - 5, - 2 ], [ 2, 5 ], [ 5, 3 ], [ 3, - 5 ], [ - 2, 6 ], [ 0, - 7 ], [ - 4, - 6 ], [ - 6, 4 ], [ - 8, 0 ], [ 7, - 4 ], [ 6, 7 ], [ - 7, - 8 ]], [[ - 4, - 7 ], [ - 7, - 5 ], [ - 3, - 5 ], [ - 5, - 4 ], [ - 1, - 4 ], [ - 2, - 2 ], [ - 6, - 1 ], [ - 4, 0 ], [ - 7, 1 ], [ - 1, 2 ], [ - 6, 3 ], [ - 3, 3 ], [ - 7, 6 ], [ - 3, 6 ], [ - 5, 7 ], [ - 1, 7 ], [ 5, - 7 ], [ 1, - 6 ], [ 6, - 5 ], [ 4, - 4 ], [ 2, - 3 ], [ 7, - 2 ], [ 1, - 1 ], [ 4, - 1 ], [ 2, 1 ], [ 6, 2 ], [ 0, 4 ], [ 4, 4 ], [ 2, 5 ], [ 7, 5 ], [ 5, 6 ], [ 3, 7 ]]];

	THREE.SSAARenderPass = SSAARenderPass;

} )();