shader_type spatial;


float height_at(float x, float z, float time) {
    float height = sin(0.25*x-time*0.75);
    return height + 1.0;
}

vec3 normal_at(float x, float z, float time) {
    float u = 0.01;
    float left = height_at(x - u, z, time);
    float right = height_at(x + u, z, time);
    float back = height_at(x, z - u, time);
    float fore = height_at(x, z + u, time);
    vec3 n = normalize(vec3(left - right, 2.0, back - fore));
    return n;
}

void vertex() {
    NORMAL = normal_at(VERTEX.x, VERTEX.z, TIME);
    VERTEX.y = height_at(VERTEX.x, VERTEX.z, TIME);
}