//Renderer.cpp
Render()// 这里你需要为每个像素生成一条对应的光线，
        //然后调用函数 castRay() 来得到颜色，
        //最后将颜色存储在帧缓冲区的相应像素中。
//Triangle.hpp
rayTriangleIntersect()// v0, v1, v2 是三角形的三个顶点，
                      //orig 是光线的起点，dir 是光线单位化的方向向量。
                      //tnear, u, v 是你需要使用我们课上推导的
                      //Moller-Trumbore 算法来更新的参数。

void Renderer::Render(const Scene &scene) {
  std::vector<Vector3f> framebuffer(scene.width * scene.height);

  float scale = std::tan(deg2rad(scene.fov * 0.5f));
  float imageAspectRatio = scene.width / (float)scene.height;

  // Use this variable as the eye position to start your rays.
  Vector3f eye_pos(0);
  int m = 0;
  for (int j = 0; j < scene.height; ++j) {
    for (int i = 0; i < scene.width; ++i) {
      // generate primary ray direction
      float x;
      float y;
      // Find the x and y positions of the current pixel to get the
      // direction vector that passes through it. Also, don't forget to
      // multiply both of them with the variable *scale*, and x
      // (horizontal) variable with the *imageAspectRatio*

      x = (2 * (i + 0.5) / (float)scene.width - 1) * scale * imageAspectRatio;
      y = (1 - 2 * (j + 0.5) / (float)scene.height) * scale;

      Vector3f dir =
          Vector3f(x, y, -1); // Don't forget to normalize this direction!
      dir = normalize(dir);
      framebuffer[m++] = castRay(eye_pos, dir, scene, 0);
    }
    UpdateProgress(j / (float)scene.height);
  }

  // save framebuffer to file
  FILE *fp = fopen("binary.ppm", "wb");
  (void)fprintf(fp, "P6\n%d %d\n255\n", scene.width, scene.height);
  for (auto i = 0; i < scene.height * scene.width; ++i) {
    static unsigned char color[3];
    color[0] = (char)(255 * clamp(0, 1, framebuffer[i].x));
    color[1] = (char)(255 * clamp(0, 1, framebuffer[i].y));
    color[2] = (char)(255 * clamp(0, 1, framebuffer[i].z));
    fwrite(color, 1, 3, fp);
  }
  fclose(fp);
}

bool rayTriangleIntersect(const Vector3f &v0, const Vector3f &v1,
                          const Vector3f &v2, const Vector3f &orig,
                          const Vector3f &dir, float &tnear, float &u,
                          float &v) {
  // Implement this function that tests whether the triangle
  // that's specified bt v0, v1 and v2 intersects with the ray (whose
  // origin is *orig* and direction is *dir*)
  // Also don't forget to update tnear, u and v.

  // Moller-Trumbore
  Vector3f e1 = v1 - v0;
  Vector3f e2 = v2 - v0;
  Vector3f s = orig - v0;
  Vector3f s1 = crossProduct(dir, e2);
  Vector3f s2 = crossProduct(s, e1);
  float t = dotProduct(s2, e2) / dotProduct(s1, e1);
  float b1 = dotProduct(s1, s) / dotProduct(s1, e1);
  float b2 = dotProduct(s2, dir) / dotProduct(s1, e1);
  if (t > 0.0 && b1 > 0.0 && b2 > 0.0 && (1 - b1 - b2) > 0.0) {
    tnear = t;
    u = b1;
    v = b2;
    return true;
  }
  return false;
}