So, why does path tracing require quadrillions of calculations?

那么，为什么路径追踪需要数千万亿次计算呢？

There are many different ray  tracing algorithms used to render scenes, but the current industry standard in TV  shows and movies is called path tracing.

有许多不同的光线追踪算法用于渲染场景，但目前电视节目和电影的行业标准称为路径追踪。

If we solve this light transport problem between these point light sources, we get a solution that is remarkably similar to the original solution with path tracing, however, solving this new representation is much simpler.

如果我们解决这些点光源之间的光传输问题，我们就能得到一个方案，它与原来路径跟踪的方法非常相似，然而解决这个新的课题却要简单得多。

It's called path tracing because by using these  primary rays, secondary rays and shadow rays, we're finding billions of paths from the camera  through different points in the scene and to the light sources.

它被称为路径追踪，因为通过使用这些主射线、次射线和阴影射线，我们可以找到从相机穿过场景中的不同点到光源的数十亿条路径。

Furthermore,   animations typically have 24 frames a second, so a 20-minute animation requires over a  quadrillion rays, and that's why path tracing was considered computationally impossible for  TV shows and movies for decades.

此外， 动画通常每秒有 24 帧，因此 20 分钟的动画需要超过一千万亿条射线，这就是为什么几十年来电视节目和电影中的路径追踪被认为在计算上是不可能的。

Here's an  interesting scene of some glass and mirror objects that truly show the power of path tracing, and  you can see multiple mirror bounces in some of the objects and proper refraction in the glass.

这里有一些玻璃和镜子物体的有趣场景， 真正展示了路径追踪的力量，并且您可以在一些物体中看到多次镜面反射， 在玻璃中看到适当的折射。