PMREMGenerator: Fix `fromScene()` back-side materials (#30063)

* Fix `fromScene()` back-side materials

* Update PMREMGenerator.js

* Update PMREMGenerator.js

src/nodes/pmrem/PMREMNode.js

@@ -297,6 +297,8 @@ class PMREMNode extends TempNode {
 
 		}
 
+		uvNode = vec3( uvNode.x, uvNode.y.negate(), uvNode.z );
+
 		//
 
 		let levelNode = this.levelNode;

src/renderers/common/extras/PMREMGenerator.js

@@ -78,7 +78,7 @@ const _faceLib = [
 ];
 
 const direction = getDirection( uv(), attribute( 'faceIndex' ) ).normalize();
-const outputDirection = vec3( direction.x, direction.y.negate(), direction.z );
+const outputDirection = vec3( direction.x, direction.y, direction.z );
 
 /**
  * This class generates a Prefiltered, Mipmapped Radiance Environment Map
@@ -406,8 +406,8 @@ class PMREMGenerator {
 		cubeCamera.far = far;
 
 		// px, py, pz, nx, ny, nz
-		const upSign = [ - 1, 1, - 1, - 1, - 1, - 1 ];
-		const forwardSign = [ 1, 1, 1, - 1, - 1, - 1 ];
+		const upSign = [ 1, 1, 1, 1, - 1, 1 ];
+		const forwardSign = [ 1, - 1, 1, - 1, 1, - 1 ];
 
 		const renderer = this._renderer;