Is there any way to implement a 2D image layer above the 3D scene in just one Canvas?
Although Cesium doesn’t have direct support for this, it’s possible – but it is unnecessary in most cases. The easiest thing would be to just overlay normal html elements over the viewer renders.
We are trying to use billboard whose size is same with canvas to realize this effect.
Tristan, there’s no need to use a billboard or any Cesium-specific construct for this, you can just overlay an image on top of Cesium via HTML. Here’s an example: http://analyticalgraphicsinc.github.io/cesium-google-earth-examples/examples/screenFrame.html
There is good effect by this way, but we want render all element on just canvas so that we can parse content background to generate video...