three.js/examples/js/postprocessing/ClearPass.js

THREE.ClearPass = function ( clearColor, clearAlpha ) {

	THREE.Pass.call( this );

	this.needsSwap = false;

	this.clearColor = ( clearColor !== undefined ) ? clearColor : 0x000000;
	this.clearAlpha = ( clearAlpha !== undefined ) ? clearAlpha : 0;
	this._oldClearColor = new THREE.Color();

};

THREE.ClearPass.prototype = Object.assign( Object.create( THREE.Pass.prototype ), {

	constructor: THREE.ClearPass,

	render: function ( renderer, writeBuffer, readBuffer /*, deltaTime, maskActive */ ) {

		var oldClearAlpha;

		if ( this.clearColor ) {

			renderer.getClearColor( this._oldClearColor );
			oldClearAlpha = renderer.getClearAlpha();

			renderer.setClearColor( this.clearColor, this.clearAlpha );

		}

		renderer.setRenderTarget( this.renderToScreen ? null : readBuffer );
		renderer.clear();

		if ( this.clearColor ) {

			renderer.setClearColor( this._oldClearColor, oldClearAlpha );

		}

	}

} );