Why custom material by glsl is not display

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;