/*
 * Tuxánci 2 - A first person shooter
 * Copyright (C) 2007-2011  Tuxánci Development Team
 * Copyright (C) 2025-2026  Connor Thomson
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

struct FSInput {
    float3 normal          : TEXCOORD0;
    float3 world_position  : TEXCOORD1;
    float3 camera_position : TEXCOORD2;
};

struct FSOutput {
    float4 out_color : SV_Target0;
};

static const float ambient_strength  = 0.22;
static const float diffuse_strength  = 0.78;
static const float specular_strength = 0.6;
static const float shininess         = 32.0;

FSOutput main(FSInput input) {
    float3 light_direction = normalize(float3(-0.45, 0.75, 0.55));
    float3 normal = normalize(input.normal);
    float3 view_direction = normalize(input.camera_position - input.world_position);
    float3 reflect_direction = reflect(-light_direction, normal);

    float diffuse = max(dot(normal, light_direction), 0.0);
    float specular = diffuse > 0.0 ? pow(max(dot(view_direction, reflect_direction), 0.0), shininess) : 0.0;

    float shade = saturate(ambient_strength + diffuse * diffuse_strength + specular * specular_strength);
    FSOutput output;
    output.out_color = float4(shade, shade, shade, 1.0);
    return output;
}