jtBaseApp/node_modules/cesium/Source/Shaders/Materials/NormalMapMaterial.glsl

uniform sampler2D image;
uniform float strength;
uniform vec2 repeat;

czm_material czm_getMaterial(czm_materialInput materialInput)
{
    czm_material material = czm_getDefaultMaterial(materialInput);
    
    vec4 textureValue = texture2D(image, fract(repeat * materialInput.st));
    vec3 normalTangentSpace = textureValue.channels;
    normalTangentSpace.xy = normalTangentSpace.xy * 2.0 - 1.0;
    normalTangentSpace.z = clamp(1.0 - strength, 0.1, 1.0);
    normalTangentSpace = normalize(normalTangentSpace);
    vec3 normalEC = materialInput.tangentToEyeMatrix * normalTangentSpace;
    
    material.normal = normalEC;
    
    return material;
}