Phong fragment shader with material

#version 300 core

layout(location = 0) in vec3 frag_position;
layout(location = 1) in vec3 frag_normal;
layout(location = 2) in vec2 frag_uv;

layout(location = 0) out vec4 frag_color;

struct Light {
    vec3 position;
    vec3 color;
};

struct Material {
    vec3 ambient;
    vec3 diffuse;
    vec3 specular;
    float shininess;
};

uniform sampler2D u_texture;
uniform Light     u_light;
uniform Material  u_material;
uniform vec3      u_view_position; // ONLY IF WE DON'T USE MODEL_VIEW!

void main() {
    vec3 normal = normalize(frag_normal);
    vec3 texel = texture(u_texture, frag_uv).rgb;

    // AMBIENT COMPONENT
    vec3 ambient = u_material.ambient * u_light.color; // you could use texel as well

    // DIFFUSE COMPONENT
    vec3 to_light = normalize(u_light.position - frag_position);
    float diffuse_impact = max(dot(to_light, normal), 0.0);
    vec3 diffuse = u_material.diffuse * diffuse_impact;

    // SPECULAR COMPONENT
    vec3 reflected = normalize(reflect(-to_light, normal));
    vec3 to_eye = normalize(u_view_position - frag_position); // ONLY IF WE DON'T USE MODEL_VIEW!
    // vec3 to_eye = normalize(-frag_position); // If we use MODEL_VIEW
    float specular_impact = max(dot(reflected, to_eye), 0.0);
    float specular_reformed = pow(specular_impact, u_material.shininess);

    // GETTING RESULT FRAGMENT COLOR:
    frag_color = vec4((ambient + diffuse + specular) * texel, 1.0);
}