struct Light {
    vec4 pos[MAX_LIGHTS]; // w == 0 -> directional light
    vec3 color[MAX_LIGHTS];
    float constantAttenuation[MAX_LIGHTS], linearAttenuation[MAX_LIGHTS], quadraticAttenuation[MAX_LIGHTS];
    float spotCutoff[MAX_LIGHTS], spotExponent[MAX_LIGHTS];
    vec3 spotDir[MAX_LIGHTS];
};

uniform Light lights;