(https://cesium.com/learn/cesiumjs/ref-doc/PostProcessStage.html?classFilter=PostProcessStage)
uniforms:An object whose properties will be used to set the shaders uniforms. The properties can be constant values or a function. A constant value can also be a URI, data URI, or HTML element to use as a texture.
can you show me how to declare a texture in uniform and how to get in fragment