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// [comment]
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// The main render function. This where we iterate over all pixels in the image, generate
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// primary rays and cast these rays into the scene. The content of the framebuffer is
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// saved to a file.
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// [/comment]
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void Renderer::Render(const Scene& scene)
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{
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    std::vector<Vector3f> framebuffer(scene.width * scene.height);
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    float scale = std::tan(deg2rad(scene.fov * 0.5f));
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    float imageAspectRatio = scene.width / (float)scene.height;
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    // Use this variable as the eye position to start your rays.
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    Vector3f eye_pos(0);
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    int m = 0;
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    for (int j = 0; j < scene.height; ++j)
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    {
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        for (int i = 0; i < scene.width; ++i)
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        {
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            // generate primary ray direction
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            float x;
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            float y;
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            // TODO: Find the x and y positions of the current pixel to get the direction
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            // vector that passes through it.
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            // Also, don't forget to multiply both of them with the variable *scale*, and
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            // x (horizontal) variable with the *imageAspectRatio*
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            x = (2 * (i + 0.5f) / (float)scene.width - 1) * imageAspectRatio * scale;
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            y = (1 - 2 * (j + 0.5f) / (float)scene.height) * scale;
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            Vector3f dir = normalize(Vector3f(x, y, -1)); // Don't forget to normalize this direction!
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            framebuffer[m++] = castRay(eye_pos, dir, scene, 0);
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        }
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        UpdateProgress(j / (float)scene.height);
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    }
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    // save framebuffer to file
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    FILE* fp = fopen("binary.ppm", "wb");
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    (void)fprintf(fp, "P6\n%d %d\n255\n", scene.width, scene.height);
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    for (auto i = 0; i < scene.height * scene.width; ++i) {
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        static unsigned char color[3];
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        color[0] = (char)(255 * clamp(0, 1, framebuffer[i].x));
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        color[1] = (char)(255 * clamp(0, 1, framebuffer[i].y));
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        color[2] = (char)(255 * clamp(0, 1, framebuffer[i].z));
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        fwrite(color, 1, 3, fp);
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    }
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    fclose(fp);
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}

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bool rayTriangleIntersect(const Vector3f &v0, const Vector3f &v1,
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                          const Vector3f &v2, const Vector3f &orig,
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                          const Vector3f &dir, float &tnear, float &u,
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                          float &v) {
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  // TODO: Implement this function that tests whether the triangle
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  // that's specified bt v0, v1 and v2 intersects with the ray (whose
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  // origin is *orig* and direction is *dir*)
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  // Also don't forget to update tnear, u and v.
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  constexpr float kEpsilon = 1e-8f;
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  const Vector3f e1 = v1 - v0;
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  const Vector3f e2 = v2 - v0;
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  const Vector3f s1 = crossProduct(dir, e2);
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  const float det = dotProduct(e1, s1);
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  // 判断射线和平面是否平行
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  if (std::fabs(det) < kEpsilon) {
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    return false;
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  }
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  const float invDet = 1.0f / det;
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  const Vector3f s = orig - v0;
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  u = dotProduct(s, s1) * invDet;
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  // 约束重心坐标u在[0, 1]范围内
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  if (u < 0.0f || u > 1.0f) {
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    return false;
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  }
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  const Vector3f s2 = crossProduct(s, e1);
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  v = dotProduct(dir, s2) * invDet;
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  // 约束重心坐标v在[0, 1]范围内，并且u + v <= 1，保证交点在三角形内部
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  if (v < 0.0f || u + v > 1.0f) {
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    return false;
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  }
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  tnear = dotProduct(e2, s2) * invDet;
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  return tnear > kEpsilon;
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}