// Copyright (C) 2022 RozK
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

#version 320 es
precision highp float;

in vec4 v_position; // view space
in vec4 v_normal; // view space
in vec4 v_terrain_normal; // view space (x, y, z, weight)
in vec4 v_texcoord; // texture space (s, t, pixel_level, material_level)

#define v_weight v_terrain_normal.w

uniform vec3 u_light_direction; // view space (-direction_x, -direction_y, -direction_z)
uniform vec3 u_light_color; // (color.r * power, color.g * power, color.b * power)

layout(binding=0) uniform highp sampler2DArray u_texture_sampler;

layout(location = 0) out vec4 o_color;

void main(void) {
    vec4 pixel = texture(u_texture_sampler, v_texcoord.stp);
    vec4 material = texture(u_texture_sampler, v_texcoord.stq);
    #define m_metallic material.x
    #define m_specular material.y
    #define m_roughness material.z
    vec3 normal = normalize(v_normal.xyz);
    vec3 eye_dir = -normalize(v_position.xyz);
    float d = dot(normal, u_light_direction);
    float halfd = 0.5 + d * 0.5;
    float td = dot(normalize(v_terrain_normal.xyz), u_light_direction);
    float diffuse = halfd * mix(halfd, 0.5 + td * 0.5, v_weight) * (1.0 - m_metallic);
    float s = max(0.0, dot(normal, normalize(u_light_direction + eye_dir)));
    float shininess = 1.0 + pow(1.0 - m_roughness, 2.0) * 999.0;
    float stepd = step(0.0, d);
    float specular = pow(s, shininess) * mix(stepd, stepd * max(0.0, td), v_weight);
    vec3 color = pixel.rgb * u_light_color;
    o_color = vec4(
        vec3(
            color * diffuse +
            color * (specular * m_metallic) +
            u_light_color * (specular * m_specular)),
        pixel.a);
}