setStencilOp( stencilFail, stencilZFail, stencilZPass ) {

		if ( this.currentStencilFail !== stencilFail ||
			 this.currentStencilZFail !== stencilZFail ||
			 this.currentStencilZPass !== stencilZPass ) {

			this.gl.stencilOp( stencilFail, stencilZFail, stencilZPass );

			this.currentStencilFail = stencilFail;
			this.currentStencilZFail = stencilZFail;
			this.currentStencilZPass = stencilZPass;

		}

	}
Specifies whether the stencil test operation.

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

@param {number} stencilFail - The function to use when the stencil test fails.
@param {number} stencilZFail - The function to use when the stencil test passes, but the depth test fail.
@param {number} stencilZPass - The function to use when both the stencil test and the depth test pass,
or when the stencil test passes and there is no depth buffer or depth testing is disabled.