Why custom material by glsl is not display

CesiumJS
1

What is the difference between polyline and polylinevolume，In terms of image texture settings？
I want to custom material by glsl，but why the image is not displayed？
for example


 `czm_material czm_getMaterial(czm_materialInput materialInput)
	{
		 czm_material material = czm_getDefaultMaterial(materialInput);
		 vec2 st = materialInput.st;
		 vec4 colorImage = texture2D(image, vec2(fract(st.s*repeat.x - time),fract(st.t*repeat.y)* czm_pi));
		 material.alpha = colorImage.a * color.a;
		 material.diffuse = color.rgb;
		 return material;
	 }`;