Update the resolution of image in shader

Hi guys, i’m trying to use custom materails to polyline .it’s work fine. (ex: pic1);

But when i zoom in map, i found that image won’t update the resolution.(ex: pic2);

here is the main code of shader:

“czm_material czm_getMaterial(czm_materialInput materialInput)” +
“{” +
“czm_material material = czm_getDefaultMaterial(materialInput);” +
“vec2 st = materialInput.st;” +
“vec4 colorImage = texture2D(image, vec2(fract(30.0*st.s), fract(st.t)));” +
“material.alpha = colorImage.a;” +
“material.diffuse = colorImage.rgb;” +
“return material;” +

What could i do to solve this problem?