ray tracing in one weekend - 3

8 Antialiasing

如何采样？

采样以像素为中心的正方形区域，该区域延伸到四个相邻像素中的每个像素的一半。

使用随机数

#include <cstdlib>

inline double random_double() {
    // Returns a random real in [0,1).
    return rand() / (RAND_MAX + 1.0);
}

inline double random_double(double min, double max) {
    // Returns a random real in [min,max).
    return min + (max-min)*random_double();
}

修改一下 color.h

#include "interval.h"
#include "vec3.h"

using color = vec3;

void write_color(std::ostream& out, const color& pixel_color) {
    auto r = pixel_color.x();
    auto g = pixel_color.y();
    auto b = pixel_color.z();

    // Translate the [0,1] component values to the byte range [0,255].
    static const interval intensity(0.000, 0.999);
    int rbyte = int(256 * intensity.clamp(r));
    int gbyte = int(256 * intensity.clamp(g));
    int bbyte = int(256 * intensity.clamp(b));

    // Write out the pixel color components.
    out << rbyte << ' ' << gbyte << ' ' << bbyte << '\n';
}

修改 camera

class camera {
  public:
    double aspect_ratio      = 1.0;  // Ratio of image width over height
    int    image_width       = 100;  // Rendered image width in pixel count
    int    samples_per_pixel = 10;   // Count of random samples for each pixel

    void render(const hittable& world) {
        initialize();

        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++) {
                color pixel_color(0,0,0);
                for (int sample = 0; sample < samples_per_pixel; sample++) {
                    ray r = get_ray(i, j);
                    pixel_color += ray_color(r, world);
                }
                write_color(std::cout, pixel_samples_scale * pixel_color);
            }
        }

        std::clog << "\rDone.                 \n";
    }
    ...
  private:
    int    image_height;         // Rendered image height
    double pixel_samples_scale;  // Color scale factor for a sum of pixel samples
    point3 center;               // Camera center
    point3 pixel00_loc;          // Location of pixel 0, 0
    vec3   pixel_delta_u;        // Offset to pixel to the right
    vec3   pixel_delta_v;        // Offset to pixel below

    void initialize() {
        image_height = int(image_width / aspect_ratio);
        image_height = (image_height < 1) ? 1 : image_height;

        pixel_samples_scale = 1.0 / samples_per_pixel;

        center = point3(0, 0, 0);
        ...
    }

    ray get_ray(int i, int j) const {
        // Construct a camera ray originating from the origin and directed at randomly sampled
        // point around the pixel location i, j.

        auto offset = sample_square();
        auto pixel_sample = pixel00_loc
                          + ((i + offset.x()) * pixel_delta_u)
                          + ((j + offset.y()) * pixel_delta_v);

        auto ray_origin = center;
        auto ray_direction = pixel_sample - ray_origin;

        return ray(ray_origin, ray_direction);
    }

    vec3 sample_square() const {
        // Returns the vector to a random point in the [-.5,-.5]-[+.5,+.5] unit square.
        return vec3(random_double() - 0.5, random_double() - 0.5, 0);
    }

    color ray_color(const ray& r, const hittable& world) const {
        ...
    }
};

#endif