基础光线追踪(4) - 球

bool isCollide(const Ray &r, const Point3f &o, float radius) {
    Vector3f p = r.getOrigin() - o;
    float a = dot(p, r.getDir());
    return p.length2() - a * a < radius * radius;
}

#include "../3rdParty/svpng/svpng.inc"
#include "../Chapter3/Ray.h"

#include <cstdio>

const int WIDTH = 640;
const int HEIGHT = 480;

using byte = unsigned char;

void paint(byte *d, int x, int y, Color3f color, float alpha) {
    d += 4 * (y * WIDTH + x);
    d[0] = 255 * color.r;
    d[1] = 255 * color.g;
    d[2] = 255 * color.b;
    d[3] = 255 * alpha;
}

Color3f mix(const Color3f &a, const Color3f &b, float t) { return a * (1.0f - t) + b * t; }

bool isCollide(const Ray &r, const Point3f &o, float radius) {
    Vector3f p = r.getOrigin() - o;
    float a = dot(p, r.getDir());
    return p.length2() - a * a < radius * radius;
}

Color3f paint(const Ray &r) {
    if (isCollide(r, {0.0f, 0.0f, -1.0f}, 0.5f)) return {1.0f, 0.0f, 0.0f};
    Vector3f dir = r.getDir();
    float t = 0.5f * (dir.y + 1.0f);
    return mix({1.0f, 1.0f, 1.0f}, {0.5f, 0.7f, 1.0f}, t);
}

int main() {
    byte d[4 * WIDTH * HEIGHT];
    FILE *f = fopen("ch4.png", "wb");
    Point3f lowerLeftCorner(-2.0f, -1.5f, -1.0f);
    Vector3f horizonal(4.0f, 0.0f, 0.0f);
    Vector3f vertical(0.0f, 3.0f, 0.0f);
    Point3f origin(0.0f, 0.0f, 0.0f);

    for (int x = 0; x < WIDTH; x++) {
        for (int y = 0; y < HEIGHT; y++) {
            float u = (float)x / WIDTH;
            float v = (float)y / HEIGHT;
            Ray r(origin, lowerLeftCorner + u * horizonal + v * vertical);
            paint(d, x, y, paint(r), 1.0f);
        }
    }
    svpng(f, WIDTH, HEIGHT, d, 1);
    fclose(f);
}