ingle fixed-point or floating-point value that
                    specifies whether one- or two-sided lighting calculations
                    are done for polygons. It has no effect on the lighting
                    calculations for points or lines. If
                    <em class="parameter"><code>params</code></em>
                    is 0, one-sided lighting is specified, and both front- and
                    back-facing polygons are assigned the same computed color.
                    Otherwise