setDepthFunc( depthFunc ) {

		if ( this.currentDepthFunc !== depthFunc ) {

			const { gl } = this;

			switch ( depthFunc ) {

				case NeverDepth:

					gl.depthFunc( gl.NEVER );
					break;

				case AlwaysDepth:

					gl.depthFunc( gl.ALWAYS );
					break;

				case LessDepth:

					gl.depthFunc( gl.LESS );
					break;

				case LessEqualDepth:

					gl.depthFunc( gl.LEQUAL );
					break;

				case EqualDepth:

					gl.depthFunc( gl.EQUAL );
					break;

				case GreaterEqualDepth:

					gl.depthFunc( gl.GEQUAL );
					break;

				case GreaterDepth:

					gl.depthFunc( gl.GREATER );
					break;

				case NotEqualDepth:

					gl.depthFunc( gl.NOTEQUAL );
					break;

				default:

					gl.depthFunc( gl.LEQUAL );

			}

			this.currentDepthFunc = depthFunc;

		}

	}
Specifies the depth compare function.

This method caches the state so `gl.depthFunc()` is only
called when necessary.

@param {number} depthFunc - The depth compare function.