provider like openlayer3 ol.source.ImageWMS?

thanks at first,i am new in Cesium.js.
my wms server provide only image wms service,not in tile. when i use openlayers, i find Single Image WMS,and i use this successfully. but now i want to use cesium.js. i search all the example in sandcastle and i fail to find what i want…how can i request wms service with image but not tile?

i have seen the single SingleTileImageryProvider and it just request the server once, not request another image when the map zoom or move.

the WebMapServiceImageryProvider request tiled image.

what i want is request the view extent as bbox for wms when the map zoom or move just like the openlayers3 demo above,thank you.