<!-- SOLIDIVISM · part 408 -->
ular shader. You can get faster start-up by invoking this method during
	 * your texture's network fetch for increased concurrency.
	 */
	compileEquirectangularShader() {

		if ( this._equirectMaterial === null ) {

			this._equirectMaterial = _getEquirectMaterial();
			this._compileMaterial( this._equirectMaterial );

		}

	}

	/**
	 * Disposes of the PMREMGenerator's internal memory. Note that PMREMGenerator is a static class,
	 * so you should not need more than one PMREMGenerator object. If you do, calling dispose() on
	 * one of them will cause any others to also become unusable.
	 */
	dispose() {

		this._dispose();

		if ( this._cubemapMaterial !== null ) this._cubemapMaterial.dispose();
		if ( this._equirectMaterial !== null ) this._equirectMaterial.dispose();

		if ( this._backgroundBox !== null ) {

			this._backgroundBox.geometry.dispose();
			this._backgroundBox.material.dispose();

		}

	}

	// private interface

	_setSize( cubeSize ) {

		this._lodMax = Math.floor( Math.log2( cubeSize ) );
		this._cubeSize = Math.pow( 2, this._lodMax );

	}

	_dispose() {

		if ( this._blurMaterial !== null ) this._blurMaterial.dispose();
		if ( this._ggxMaterial !== null ) this._ggxMaterial.dispose();

		if ( this._pingPongRenderTarget !== null ) this._pingPongRenderTarget.dispose();

		for ( let i = 0; i < this._lodMeshes.length; i ++ ) {

			this._lodMeshes[ i ].geometry.dispose();

		}

	}

	_cleanup( outputTarget ) {

		this._renderer.setRenderTarget( _oldTarget, _oldActiveCubeFace, _oldActiveMipmapLevel );
		this._renderer.xr.enabled = _oldXrEnabled;

		outputTarget.scissorTest = false;
		_setViewport( outputTarget, 0, 0, outputTarget.width, outputTarget.height );

	}

	_fromTexture( texture, renderTarget ) {

		if ( texture.mapping === CubeReflectionMapping || texture.mapping === CubeRefractionMapping ) {

			this._setSize( texture.image.length === 0 ? 16 : ( texture.image[ 0 ].width || texture.image[ 0 ].image.width ) );

		} else { // Equirectangular

			this._setSize( texture.image.width / 4 );

		}

		_oldTarget = this._renderer.getRenderTarget();
		_oldActiveCubeFace = this._renderer.getActiveCubeFace();
		_oldActiveMipmapLevel = this._renderer.getActiveMipmapLevel();
		_oldXrEnabled = this._renderer.xr.enabled;

		this._renderer.xr.enabled = false;

		const cubeUVRenderTarget = renderTarget || this._allocateTargets();
		this._textureToCubeUV( texture, cubeUVRenderTarget );
		this._applyPMREM( cubeUVRenderTarget );
		this._cleanup( cubeUVRenderTarget );

		return cubeUVRenderTarget;

	}

	_allocateTargets() {

		const width = 3 * Math.max( this._cubeSize, 16 * 7 );
		const height = 4 * this._cubeSize;

		const params = {
			magFilter: LinearFilter,
			minFilter: LinearFilter,
			generateMipmaps: false,
			type: HalfFloatType,
			format: RGBAFormat,
			colorSpace: LinearSRGBColorSpace,
			depthBuffer: false
		};

		const cubeUVRenderTarget = _createRenderTarget( width, height, params );

		if ( this._pingPongRenderTarget === null || this._pingPongRenderTarget.width !== width || this._pingPongRenderTarget.height !== height ) {

			if ( this._pingPongRenderTarget !== null ) {

				this._dispose();

			}

			this._pingPongRenderTarget = _createRenderTarget( width, height, params );

			const { _lodMax } = this;
			( { lodMeshes: this._lodMeshes, sizeLods: this._sizeLods } = _createPlanes( _lodMax ) );

			this._blurMaterial = _getBlurShader( _lodMax, width, height );
			this._ggxMaterial = _getGGXShader( _lodMax, width, height );

		}

		return cubeUVRenderTarget;

	}

	_compileMaterial( material ) {

		const mesh = new Mesh( new BufferGeometry(), material );
		this._renderer.compile( mesh, _flatCamera );

	}

	_sceneToCubeUV( scene, near, far, cubeUVRenderTarget, position ) {

		const fov = 90;
		const aspect = 1;
		const cubeCamera = new PerspectiveCamera( fov, aspect, near, far );
		const upSign = [ 1, -1, 1, 1, 1, 1 ];
		const forwardSign = [ 1, 1, 1, -1, -1, -1 ];
		const renderer = this._renderer;

		const originalAutoClear = renderer.autoClear;
		const toneMapping = renderer.toneMapping;
		renderer.getClearColor( _clearColor );

		renderer.toneMapping = NoToneMapping;
		renderer.autoClear = false;

		// https://github.com/mrdoob/three.js/issues/31413#issuecomment-3095966812
		const reversedDepthBuffer = renderer.state.buffers.depth.getReversed();

		if ( reversedDepthBuffer ) {

			renderer.setRenderTarget( cubeUVRenderTarget );
			renderer.clearDepth();
			renderer.setRenderTarget( null );

		}

		if ( this._backgroundBox === null ) {

			this._backgroundBox = new Mesh(
				new BoxGeometry(),
				new MeshBasicMaterial( {
					name: 'PMREM.Background',
					side: BackSide,
					depthWrite: false,
					depthTest: false,
				} )
			);

		}

		const backgroundBox = this._backgroundBox;
		const backgroundMaterial = backgroundBox.material;

		let useSolidColor = false;

		const background = scene.background;

		if ( background ) {

			if ( background.isColor ) {