convert( p, colorSpace = NoColorSpace ) {

		const { gl, extensions } = this;

		let extension;

		const transfer = ColorManagement.getTransfer( colorSpace );

		if ( p === UnsignedByteType ) return gl.UNSIGNED_BYTE;
		if ( p === UnsignedShort4444Type ) return gl.UNSIGNED_SHORT_4_4_4_4;
		if ( p === UnsignedShort5551Type ) return gl.UNSIGNED_SHORT_5_5_5_1;
		if ( p === UnsignedInt5999Type ) return gl.UNSIGNED_INT_5_9_9_9_REV;

		if ( p === ByteType ) return gl.BYTE;
		if ( p === ShortType ) return gl.SHORT;
		if ( p === UnsignedShortType ) return gl.UNSIGNED_SHORT;
		if ( p === IntType ) return gl.INT;
		if ( p === UnsignedIntType ) return gl.UNSIGNED_INT;
		if ( p === FloatType ) return gl.FLOAT;

		if ( p === HalfFloatType ) {

			return gl.HALF_FLOAT;

		}

		if ( p === AlphaFormat ) return gl.ALPHA;
		if ( p === RGBFormat ) return gl.RGB;
		if ( p === RGBAFormat ) return gl.RGBA;
		if ( p === DepthFormat ) return gl.DEPTH_COMPONENT;
		if ( p === DepthStencilFormat ) return gl.DEPTH_STENCIL;

		// WebGL2 formats.

		if ( p === RedFormat ) return gl.RED;
		if ( p === RedIntegerFormat ) return gl.RED_INTEGER;
		if ( p === RGFormat ) return gl.RG;
		if ( p === RGIntegerFormat ) return gl.RG_INTEGER;
		if ( p === RGBAIntegerFormat ) return gl.RGBA_INTEGER;

		// S3TC

		if ( p === RGB_S3TC_DXT1_Format || p === RGBA_S3TC_DXT1_Format || p === RGBA_S3TC_DXT3_Format || p === RGBA_S3TC_DXT5_Format ) {

			if ( transfer === SRGBTransfer ) {

				extension = extensions.get( 'WEBGL_compressed_texture_s3tc_srgb' );

				if ( extension !== null ) {

					if ( p === RGB_S3TC_DXT1_Format ) return extension.COMPRESSED_SRGB_S3TC_DXT1_EXT;
					if ( p === RGBA_S3TC_DXT1_Format ) return extension.COMPRESSED_SRGB_ALPHA_S3TC_DXT1_EXT;
					if ( p === RGBA_S3TC_DXT3_Format ) return extension.COMPRESSED_SRGB_ALPHA_S3TC_DXT3_EXT;
					if ( p === RGBA_S3TC_DXT5_Format ) return extension.COMPRESSED_SRGB_ALPHA_S3TC_DXT5_EXT;

				} else {

					return null;

				}

			} else {

				extension = extensions.get( 'WEBGL_compressed_texture_s3tc' );

				if ( extension !== null ) {

					if ( p === RGB_S3TC_DXT1_Format ) return extension.COMPRESSED_RGB_S3TC_DXT1_EXT;
					if ( p === RGBA_S3TC_DXT1_Format ) return extension.COMPRESSED_RGBA_S3TC_DXT1_EXT;
					if ( p === RGBA_S3TC_DXT3_Format ) return extension.COMPRESSED_RGBA_S3TC_DXT3_EXT;
					if ( p === RGBA_S3TC_DXT5_Format ) return extension.COMPRESSED_RGBA_S3TC_DXT5_EXT;

				} else {

					return null;

				}

			}

		}

		// PVRTC

		if ( p === RGB_PVRTC_4BPPV1_Format || p === RGB_PVRTC_2BPPV1_Format || p === RGBA_PVRTC_4BPPV1_Format || p === RGBA_PVRTC_2BPPV1_Format ) {

			extension = extensions.get( 'WEBGL_compressed_texture_pvrtc' );

			if ( extension !== null ) {

				if ( p === RGB_PVRTC_4BPPV1_Format ) return extension.COMPRESSED_RGB_PVRTC_4BPPV1_IMG;
				if ( p === RGB_PVRTC_2BPPV1_Format ) return extension.COMPRESSED_RGB_PVRTC_2BPPV1_IMG;
				if ( p === RGBA_PVRTC_4BPPV1_Format ) return extension.COMPRESSED_RGBA_PVRTC_4BPPV1_IMG;
				if ( p === RGBA_PVRTC_2BPPV1_Format ) return extension.COMPRESSED_RGBA_PVRTC_2BPPV1_IMG;

			} else {

				return null;

			}

		}

		// ETC

		if ( p === RGB_ETC1_Format || p === RGB_ETC2_Format || p === RGBA_ETC2_EAC_Format ) {

			extension = extensions.get( 'WEBGL_compressed_texture_etc' );

			if ( extension !== null ) {

				if ( p === RGB_ETC1_Format || p === RGB_ETC2_Format ) return ( transfer === SRGBTransfer ) ? extension.COMPRESSED_SRGB8_ETC2 : extension.COMPRESSED_RGB8_ETC2;
				if ( p === RGBA_ETC2_EAC_Format ) return ( transfer === SRGBTransfer ) ? extension.COMPRESSED_SRGB8_ALPHA8_ETC2_EAC : extension.COMPRESSED_RGBA8_ETC2_EAC;

			} else {

				return null;

			}

		}

		// ASTC

		if ( p === RGBA_ASTC_4x4_Format || p === RGBA_ASTC_5x4_Format || p === RGBA_ASTC_5x5_Format ||
			p === RGBA_ASTC_6x5_Format || p === RGBA_ASTC_6x6_Format || p === RGBA_ASTC_8x5_Format ||
			p === RGBA_ASTC_8x6_Format || p === RGBA_ASTC_8x8_Format || p === RGBA_ASTC_10x5_Format ||
			p === RGBA_ASTC_10x6_Format || p === RGBA_ASTC_10x8_Format || p === RGBA_ASTC_10x10_Format ||
			p === RGBA_ASTC_12x10_Format || p === RGBA_ASTC_12x12_Format ) {

			extension = extensions.get( 'WEBGL_compressed_texture_astc' );

			if ( extension !== null ) {

				if ( p === RGBA_ASTC_4x4_Format ) return ( transfer === SRGBTransfer ) ? extension.COMPRESSED_SRGB8_ALPHA8_ASTC_4x4_KHR : extension.COMPRESSED_RGBA_ASTC_4x4_KHR;
				if ( p === RGBA_ASTC_5x4_Format ) return ( transfer === SRGBTransfer ) ? extension.COMPRESSED_SRGB8_ALPHA8_ASTC_5x4_KHR : extension.COMPRESSED_RGBA_ASTC_5x4_KHR;
				if ( p === RGBA_ASTC_5x5_Format ) return ( transfer === SRGBTransfer ) ? extension.COMPRESSED_SRGB8_ALPHA8_ASTC_5x5_KHR : extension.COMPRESSED_RGBA_ASTC_5x5_KHR;
				if ( p === RGBA_ASTC_6x5_Format ) return ( transfer === SRGBTransfer ) ? extension.COMPRESSED_SRGB8_ALPHA8_ASTC_6x5_KHR : extension.COMPRESSED_RGBA_ASTC_6x5_KHR;
				if ( p === RGBA_ASTC_6x6_Format ) return ( transfer === SRGBTransfer ) ? extension.COMPRESSED_SRGB8_ALPHA8_ASTC_6x6_KHR : extension.COMPRESSED_RGBA_ASTC_6x6_KHR;
				if ( p === RGBA_ASTC_8x5_Format ) return ( transfer === SRGBTransfer ) ? extension.COMPRESSED_SRGB8_ALPHA8_ASTC_8x5_KHR : extension.COMPRESSED_RGBA_ASTC_8x5_KHR;
				if ( p === RGBA_ASTC_8x6_Format ) return ( transfer === SRGBTransfer ) ? extension.COMPRESSED_SRGB8_ALPHA8_ASTC_8x6_KHR : extension.COMPRESSED_RGBA_ASTC_8x6_KHR;
				if ( p === RGBA_ASTC_8x8_Format ) return ( transfer === SRGBTransfer ) ? extension.COMPRESSED_SRGB8_ALPHA8_ASTC_8x8_KHR : extension.COMPRESSED_RGBA_ASTC_8x8_KHR;
				if ( p === RGBA_ASTC_10x5_Format ) return ( transfer === SRGBTransfer ) ? extension.COMPRESSED_SRGB8_ALPHA8_ASTC_10x5_KHR : extension.COMPRESSED_RGBA_ASTC_10x5_KHR;
				if ( p === RGBA_ASTC_10x6_Format ) return ( transfer === SRGBTransfer ) ? extension.COMPRESSED_SRGB8_ALPHA8_ASTC_10x6_KHR : extension.COMPRESSED_RGBA_ASTC_10x6_KHR;
				if ( p === RGBA_ASTC_10x8_Format ) return ( transfer === SRGBTransfer ) ? extension.COMPRESSED_SRGB8_ALPHA8_ASTC_10x8_KHR : extension.COMPRESSED_RGBA_ASTC_10x8_KHR;
				if ( p === RGBA_ASTC_10x10_Format ) return ( transfer === SRGBTransfer ) ? extension.COMPRESSED_SRGB8_ALPHA8_ASTC_10x10_KHR : extension.COMPRESSED_RGBA_ASTC_10x10_KHR;
				if ( p === RGBA_ASTC_12x10_Format ) return ( transfer === SRGBTransfer ) ? extension.COMPRESSED_SRGB8_ALPHA8_ASTC_12x10_KHR : extension.COMPRESSED_RGBA_ASTC_12x10_KHR;
				if ( p === RGBA_ASTC_12x12_Format ) return ( transfer === SRGBTransfer ) ? extension.COMPRESSED_SRGB8_ALPHA8_ASTC_12x12_KHR : extension.COMPRESSED_RGBA_ASTC_12x12_KHR;

			} else {

				return null;

			}

		}

		// BPTC

		if ( p === RGBA_BPTC_Format ) {

			extension = extensions.get( 'EXT_texture_compression_bptc' );

			if ( extension !== null ) {

				if ( p === RGBA_BPTC_Format ) return ( transfer === SRGBTransfer ) ? extension.COMPRESSED_SRGB_ALPHA_BPTC_UNORM_EXT : extension.COMPRESSED_RGBA_BPTC_UNORM_EXT;

			} else {

				return null;

			}

		}

		// RGTC

		if ( p === RED_RGTC1_Format || p === SIGNED_RED_RGTC1_Format || p === RED_GREEN_RGTC2_Format || p === SIGNED_RED_GREEN_RGTC2_Format ) {

			extension = extensions.get( 'EXT_texture_compression_rgtc' );

			if ( extension !== null ) {

				if ( p === RGBA_BPTC_Format ) return extension.COMPRESSED_RED_RGTC1_EXT;
				if ( p === SIGNED_RED_RGTC1_Format ) return extension.COMPRESSED_SIGNED_RED_RGTC1_EXT;
				if ( p === RED_GREEN_RGTC2_Format ) return extension.COMPRESSED_RED_GREEN_RGTC2_EXT;
				if ( p === SIGNED_RED_GREEN_RGTC2_Format ) return extension.COMPRESSED_SIGNED_RED_GREEN_RGTC2_EXT;

			} else {

				return null;

			}

		}

		//

		if ( p === UnsignedInt248Type ) {

			return gl.UNSIGNED_INT_24_8;

		}

		// if "p" can't be resolved, assume the user defines a WebGL constant as a string (fallback/workaround for packed RGB formats)

		return ( gl[ p ] !== undefined ) ? gl[ p ] : null;

	}
Converts the given three.js constant into a WebGL constant.
The method currently supports the conversion of texture formats
and types.

@param {number} p - The three.js constant.
@param {string} [colorSpace=NoColorSpace] - The color space.
@return {?number} The corresponding WebGL constant.