WebGLBackground: Replaced polygonOffset with gl_Position.z overwrite. See #12172.

src/renderers/shaders/ShaderLib/cube_vert.glsl

@@ -9,4 +9,6 @@ void main() {
 	#include <begin_vertex>
 	#include <project_vertex>
 
+	gl_Position.z = gl_Position.w;
+
 }

src/renderers/webgl/WebGLBackground.js

@@ -54,7 +54,6 @@ function WebGLBackground( renderer, state, geometries, premultipliedAlpha ) {
 						side: BackSide,
 						depthTest: true,
 						depthWrite: false,
-						polygonOffset: true,
 						fog: false
 					} )
 				);
@@ -64,13 +63,8 @@ function WebGLBackground( renderer, state, geometries, premultipliedAlpha ) {
 
 				boxMesh.onBeforeRender = function ( renderer, scene, camera ) {
 
-					var scale = camera.far;
-
-					this.matrixWorld.makeScale( scale, scale, scale );
 					this.matrixWorld.copyPosition( camera.matrixWorld );
 
-					this.material.polygonOffsetUnits = scale * 10;
-
 				};
 
 				geometries.update( boxMesh.geometry );