three.js/src/renderers/webgl/WebGLExtensions.js

/**
 * @author mrdoob / http://mrdoob.com/
 */

function WebGLExtensions( gl ) {

	var extensions = {};

	var isWebGL2 = ( typeof WebGL2RenderingContext !== 'undefined' && gl instanceof WebGL2RenderingContext );

	return {

		get: function ( name ) {

			if ( extensions[ name ] !== undefined ) {

				return extensions[ name ];

			}

			var extension;

			switch ( name ) {

				case 'WEBGL_depth_texture':

					if ( isWebGL2 ) {

						extension = gl;

					} else {

						extension = gl.getExtension( 'WEBGL_depth_texture' ) || gl.getExtension( 'MOZ_WEBGL_depth_texture' ) || gl.getExtension( 'WEBKIT_WEBGL_depth_texture' );

					}

					break;

				case 'EXT_texture_filter_anisotropic':
					extension = gl.getExtension( 'EXT_texture_filter_anisotropic' ) || gl.getExtension( 'MOZ_EXT_texture_filter_anisotropic' ) || gl.getExtension( 'WEBKIT_EXT_texture_filter_anisotropic' );
					break;

				case 'WEBGL_compressed_texture_s3tc':
					extension = gl.getExtension( 'WEBGL_compressed_texture_s3tc' ) || gl.getExtension( 'MOZ_WEBGL_compressed_texture_s3tc' ) || gl.getExtension( 'WEBKIT_WEBGL_compressed_texture_s3tc' );
					break;

				case 'WEBGL_compressed_texture_pvrtc':
					extension = gl.getExtension( 'WEBGL_compressed_texture_pvrtc' ) || gl.getExtension( 'WEBKIT_WEBGL_compressed_texture_pvrtc' );
					break;

				case 'WEBGL_compressed_texture_etc1':
					extension = gl.getExtension( 'WEBGL_compressed_texture_etc1' );
					break;

				default:

					if ( isWebGL2 && 
						[ 'ANGLE_instanced_arrays',
						  'OES_texture_float',
						  'OES_texture_half_float',
						  'OES_texture_half_float_linear',
						  'OES_element_index_uint',
						  'OES_standard_derivatives',
						  'EXT_frag_depth',
						  'EXT_shader_texture_lod',
						  'EXT_blend_minmax',
						  'WEBGL_draw_buffers' ].indexOf( name ) >= 0 ) {

						extension = gl;

					} else {

						extension = gl.getExtension( name );

					}

			}

			if ( extension === null ) {

				console.warn( 'THREE.WebGLRenderer: ' + name + ' extension not supported.' );

			}

			extensions[ name ] = extension;

			return extension;

		}

	};

}


export { WebGLExtensions };