three.js/src/textures/CubeTexture.js

import { Texture } from './Texture.js';
import { CubeReflectionMapping, RGBFormat } from '../constants.js';

class CubeTexture extends Texture {

	constructor( images, mapping, wrapS, wrapT, magFilter, minFilter, format, type, anisotropy, encoding ) {

		images = images !== undefined ? images : [];
		mapping = mapping !== undefined ? mapping : CubeReflectionMapping;
		format = format !== undefined ? format : RGBFormat;

		super( images, mapping, wrapS, wrapT, magFilter, minFilter, format, type, anisotropy, encoding );

		// Why CubeTexture._needsFlipEnvMap is necessary:
		//
		// By convention -- likely based on the RenderMan spec from the 1990's -- cube maps are specified by WebGL (and three.js)
		// in a coordinate system in which positive-x is to the right when looking up the positive-z axis -- in other words,
		// in a left-handed coordinate system. By continuing this convention, preexisting cube maps continued to render correctly.

		// three.js uses a right-handed coordinate system. So environment maps used in three.js appear to have px and nx swapped
		// and the flag _needsFlipEnvMap controls this conversion. The flip is not required (and thus _needsFlipEnvMap is set to false)
		// when using WebGLCubeRenderTarget.texture as a cube texture.

		this._needsFlipEnvMap = true;

		this.flipY = false;

	}

	get images() {

		return this.image;

	}

	set images( value ) {

		this.image = value;

	}

}

CubeTexture.prototype.isCubeTexture = true;

export { CubeTexture };