dispose() {

		this._dispose();

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

	}
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.