Pad each icon with one pixel on the bottom and right sides. On top of this, extra padding is added to round the widths and heights to multiples of four. This then fixes the positions of the bottom and right vertices to correctly center the icon's box around the center of the icon, not the center of the padded icon. js: 32ca4007699d1d21ab25bb38588b151510194030 fixes https://github.com/mapbox/mapbox-gl-js/issues/947