call updatePerspective when variantString changes (oldSegmentCanvas) and when component mounts (newSegmentCanvas); set default no op for updatePerspective
call updatePerspective when variantString changes (oldSegmentCanvas) and when component mounts (newSegmentCanvas); set default no op for updatePerspective

codeforamerica/streetmix,codeforamerica/streetmix,codeforamerica/streetmix