public void setPolyOffset(float factor, float units) {
        applyPolyOffset = true;
        if (factor == 0 && units == 0) {
            offsetEnabled = false;
        } else {
            offsetEnabled = true;
            offsetFactor = factor;
            offsetUnits = units;
        }
        cachedHashCode = -1;
    }
Offsets the on-screen z-order of the material's polygons, to combat visual artefacts like
stitching, bleeding and z-fighting for overlapping polygons.
Factor and units are summed to produce the depth offset.
This offset is applied in screen space,
typically with positive Z pointing into the screen.
Typical values are (1.0f, 1.0f) or (-1.0f, -1.0f)

@see <a href="http://www.opengl.org/resources/faq/technical/polygonoffset.htm">http://www.opengl.org/resources/faq/technical/polygonoffset.htm</a>
@param factor scales the maximum Z slope, with respect to X or Y of the polygon
@param units scales the minimum resolvable depth buffer value
jme3-core/src/main/java/com/jme3/material/RenderState.java