const viewer = new Cesium.Viewer('cesiumContainer')

const shader = `
in vec2 v_st;
void main()
   {
       float iTime = czm_frameNumber/100.;
       vec2 p = 2.0 * v_st - 1.;
       // vec2 p = (2.0 * gl_FragCoord.xy-czm_viewport.zw)/czm_viewport.w;

       float tau = 3.1415926535*2.0;
       float a = atan(p.x,p.y);
       float r = length(p)*0.75;
       vec2 uv = vec2(a/tau,r);

       //get the color
       float xCol = (uv.x - (iTime / 3.0)) * 3.0;
       xCol = mod(xCol, 3.0);
       vec3 horColour = vec3(0.25, 0.25, 0.25);

       if (xCol < 1.0) {

           horColour.r += 1.0 - xCol;
           horColour.g += xCol;
       }
       else if (xCol < 2.0) {

           xCol -= 1.0;
           horColour.g += 1.0 - xCol;
           horColour.b += xCol;
       }
       else {

           xCol -= 2.0;
           horColour.b += 1.0 - xCol;
           horColour.r += xCol;
       }

       // draw color beam
       uv = (2.0 * uv) - 1.0;
       float beamWidth = (0.7+0.5*cos(uv.x*10.0*tau*0.15*clamp(floor(5.0 + 10.0*cos(iTime)), 0.0, 10.0))) * abs(1.0 / (30.0 * uv.y));
       vec3 horBeam = vec3(beamWidth);
       //out_FragColor = vec4((( horBeam) * horColour), 1.0);
       vec3 color = (horBeam) * horColour;
       out_FragColor = vec4(color,color.r+color.g+color.b);
       
   }`
let xMin = 115,
  yMin = 39,
  xMax = 117,
  yMax = 41
let rect = new Cesium.Rectangle(
  Cesium.Math.toRadians(xMin),
  Cesium.Math.toRadians(yMin),
  Cesium.Math.toRadians(xMax),
  Cesium.Math.toRadians(yMax)
)

const rectangle = new Cesium.RectangleGeometry({
  rectangle: rect,
  height: 10000.0,
})
const geometry = Cesium.RectangleGeometry.createGeometry(rectangle)

let appearance = new Cesium.MaterialAppearance({
  material: new Cesium.Material({
    fabric: {
      type: 'Color',
      uniforms: {
        color: Cesium.Color.RED,
      },
    },
  }),
  fragmentShaderSource: shader,
})

const primitive = new Cesium.Primitive({
  appearance: appearance,
  geometryInstances: new Cesium.GeometryInstance({
    geometry: geometry,
  }),
  asynchronous: false,
})

viewer.scene.primitives.add(primitive)

// primitive.appearance = appearance;