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/*
* Copyright (C) 2026 Richard
*
* 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/>.
*/
#include "color.h"
#include "ray.h"
#include "vec3.h"
#include <iostream>
bool hit_sphere(const point3& center, double radius, const ray& r){
vec3 oc = center - r.origin();
auto a = dot( r.direction(), r.direction() );
auto b = -2.0 * dot( r.direction(), oc );
auto c = dot( oc, oc ) - radius * radius;
auto discriminant = b * b - 4 * a * c;
return ( discriminant >= 0 );
}
color ray_color( const ray& r )
{
if ( hit_sphere( point3( 0, 0, -1 ), 0.5, r ) )
return color( 1, 0, 0 );
vec3 unit_direction = unit_vector( r.direction() );
auto a = 0.5 * ( unit_direction.y() + 1.0 );
return ( 1.0 - a ) * color( 1.0, 1.0, 1.0 ) + a * color( 0.5, 0.7, 1.0 );
}
int main()
{
// Image
auto aspect_ratio = 16.0 / 9.0;
const int image_width = 400;
// Calculate the image height, and ensure that it's at least 1.
int image_height = static_cast<int>( image_width / aspect_ratio );
image_height = ( image_height < 1 ) ? 1 : image_height;
// Camera
auto focal_length = 1.0;
auto viewport_height = 2.0;
auto viewport_width = viewport_height * ( double( image_width ) / image_height );
auto camera_center = point3( 0, 0, 0 );
// Calculate the vectors across the horizontal and down the vertical viewport edges.
auto viewport_u = vec3( viewport_width, 0, 0 );
auto viewport_v = vec3( 0, -viewport_height, 0 );
// Calculate the horizontal and vertical delta vectors from pixel to pixel.
auto pixel_delta_u = viewport_u / image_width;
auto pixel_delta_v = viewport_v / image_height;
// Calculate the location of the upper left pixel.
auto viewport_upper_left = camera_center - vec3( 0, 0, focal_length ) - viewport_u / 2 - viewport_v / 2;
auto pixel00_loc = viewport_upper_left + 0.5 * ( pixel_delta_u + pixel_delta_v );
// Render
std::cout << "P3\n" << image_width << " " << image_height << "\n255\n";
for ( int j = 0; j < image_height; j++ ) {
std::clog << "\rScanlines remaining: " << ( image_height - j ) << ' ' << std::flush;
for ( int i = 0; i < image_width; i++ ) {
auto pixel_center = pixel00_loc + ( i * pixel_delta_u ) + ( j * pixel_delta_v );
auto ray_direction = pixel_center - camera_center;
ray r( camera_center, ray_direction );
const color pixel_color = ray_color( r );
write_color( std::cout, pixel_color );
}
}
std::clog << "\rDone. \n";
return 0;
}
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