PMREMGenerator: Fixed using compressed cubemaps. (#22699)

src/extras/PMREMGenerator.js

@@ -1,4 +1,6 @@
 import {
+	CubeReflectionMapping,
+	CubeRefractionMapping,
 	CubeUVReflectionMapping,
 	GammaEncoding,
 	LinearEncoding,
@@ -364,7 +366,9 @@ class PMREMGenerator {
 
 		const renderer = this._renderer;
 
-		if ( texture.isCubeTexture ) {
+		const isCubeTexture = ( texture.mapping === CubeReflectionMapping || texture.mapping === CubeRefractionMapping );
+
+		if ( isCubeTexture ) {
 
 			if ( this._cubemapShader == null ) {
 
@@ -382,14 +386,14 @@ class PMREMGenerator {
 
 		}
 
-		const material = texture.isCubeTexture ? this._cubemapShader : this._equirectShader;
+		const material = isCubeTexture ? this._cubemapShader : this._equirectShader;
 		const mesh = new Mesh( _lodPlanes[ 0 ], material );
 
 		const uniforms = material.uniforms;
 
 		uniforms[ 'envMap' ].value = texture;
 
-		if ( ! texture.isCubeTexture ) {
+		if ( ! isCubeTexture ) {
 
 			uniforms[ 'texelSize' ].value.set( 1.0 / texture.image.width, 1.0 / texture.image.height );