setStencilFunc( stencilFunc, stencilRef, stencilMask ) {

		if ( this.currentStencilFunc !== stencilFunc ||
			 this.currentStencilRef !== stencilRef ||
			 this.currentStencilFuncMask !== stencilMask ) {

			this.gl.stencilFunc( stencilFunc, stencilRef, stencilMask );

			this.currentStencilFunc = stencilFunc;
			this.currentStencilRef = stencilRef;
			this.currentStencilFuncMask = stencilMask;

		}

	}
Specifies whether the stencil test functions.

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

@param {number} stencilFunc - The stencil compare function.
@param {number} stencilRef - The reference value for the stencil test.
@param {number} stencilMask - A bit-wise mask that is used to AND the reference value and the stored stencil value when the test is done.