基础光线追踪(3) - 光线

编写光线并测试。

Ray

Ray.h

#ifndef _BASIC_RAY_TRACING_RAY_H_
#define _BASIC_RAY_TRACING_RAY_H_
#include "../Chapter2/Vector.h"

struct Ray {
    Ray() = default;
    Ray(const Point3f &o, const Vector3f &dir) : o(o), dir(dir) { this->dir.normalize(); }

    const Point3f &getOrigin() const { return o; }

    const Vector3f &getDir() const { return dir; }

    Point3f get(float t) const { return o + dir * t; }

    Point3f o;
    Vector3f dir;
};
#endif

测试

测试对于光线的着色，我们采用右手坐标系，假设摄像机在 $(0, 0, 0)$ 的位置，画布左下角为 $(-2, -1, -1)$，长和宽均为 $2$。

对于光线我们直接按照 $y$ 线性混合蓝色和白色来测试。

#include "../3rdParty/svpng/svpng.inc"
#include "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] = (int)255 * color.r;
    d[1] = (int)255 * color.g;
    d[2] = (int)255 * color.b;
    d[3] = (int)255 * alpha;
}

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

Color3f paint(const Ray &r) {
    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() {
    FILE *f = fopen("ch3.png", "wb");
    byte d[4 * WIDTH * HEIGHT];
    Point3f lowerLeftCorner(-2.0f, -1.0f, -1.0f);
    Vector3f horizonal(4.0f, 0.0f, 0.0f);
    Vector3f vertical(0.0f, 2.0f, 0.0f);
    Point3f origin(0.0f, 0.0f, 0.0f);

    for (int y = HEIGHT - 1; y >= 0; y--) {
        for (int x = 0; x < WIDTH; x++) {
            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);
}