#version 330 core

uniform sampler2D tex;
uniform float mesh_alpha;
uniform vec3 sun_direction;
uniform vec3 sky_color;

in vec3 surface_normal;
in vec2 frag_tex_coord;
in float frag_ambient_occlusion;
in float depth;

out vec4 color;

void main() {
    float brightness = dot(normalize(surface_normal), normalize(-sun_direction));
    vec3 diffuse = vec3(max(brightness, 0.3));

    vec4 texture_color = texture(tex, frag_tex_coord);
    if (texture_color.a < 0.5) {
        discard;
    }
    float ao = 1 - frag_ambient_occlusion / 2;

    vec3 opaque_color = diffuse * texture_color.xyz * ao;
    opaque_color = mix(sky_color, opaque_color, 1 - depth);

    color = vec4(opaque_color, mesh_alpha);
}