WebGLTextures: Fix mips gen for 3D render targets. (#22072)

src/renderers/webgl/WebGLTextures.js

@@ -122,13 +122,13 @@ function WebGLTextures( _gl, extensions, state, properties, capabilities, utils,
 
 	}
 
-	function generateMipmap( target, texture, width, height ) {
+	function generateMipmap( target, texture, width, height, depth = 1 ) {
 
 		_gl.generateMipmap( target );
 
 		const textureProperties = properties.get( texture );
 
-		textureProperties.__maxMipLevel = Math.log2( Math.max( width, height ) );
+		textureProperties.__maxMipLevel = Math.log2( Math.max( width, height, depth ) );
 
 	}
 
@@ -1230,11 +1230,11 @@ function WebGLTextures( _gl, extensions, state, properties, capabilities, utils,
 
 			if ( textureNeedsGenerateMipmaps( texture, supportsMips ) ) {
 
-				generateMipmap( _gl.TEXTURE_2D, texture, renderTarget.width, renderTarget.height );
+				generateMipmap( glTextureType, texture, renderTarget.width, renderTarget.height, renderTarget.depth );
 
 			}
 
-			state.bindTexture( _gl.TEXTURE_2D, null );
+			state.bindTexture( glTextureType, null );
 
 		}