function depth2occlusion(depthCol, newCol, threshold) {
    return new DepthToOcclusionExpr(depthCol, newCol, expr_1.wrapInValue(threshold));
}
converts a `1 / distance` depth texture to an occlusion texture, with all
occluded geometry being rendered as black
@param depthCol the color representing the inverse depth (defaults to
sampling from channel 0)
@param newCol the color to replace unoccluded areas by (defaults to white
and is mutable by default)
@param threshold values below this are not occluded (set to something low,
like 0.1 or lower; defaults to 0.01 and is mutable by default)