The Ray Tracer Challenge: Cannot get rid of acne When implement Shadows in Chapter 8.

Hi, I’m working on the Chapter 8 of the book.
After I add add the point_offset, I’m still able to see acne:

Screen Shot 2022-03-28 at 1.08.33 AM1200×807 158 KB

In the image above, I remove all balls to make things easier. I notice that for some of the hit point falls into the walls. Therefore it will have very small t (but greater than the epsilon) for the intersection.

I make all tests pass except “The Color with an intersection behind the ray”. Could some one explain that why this case can pass with the shadow? I think the light should be blocked by the outer ball.

May I get some suggestion to debug my code?

Here is my github repo: GitHub - Henrai/TheRayTracingChallenge