weird shadow geometry

[huand]

Hi, below is a cast shadow

The geometry is triangles with edges as cylinders. My question is why can we see the absence of shadows near the edge? Do i do something wrong, is there a trick I can do to avoid this, or nothing at all? thx!

[huand]

here is another view with better shadow res of the same issue:

[huand]

it looks like the cylinder edge is floating above (but its not). It looks like the center intersection of the edge shadow is not at the physical intersection of the edges

[huand]

even without edges, it looks like the faces are not connected, see below:

[asny]

The shadow map technique is quite performant and works well in most cases, that's why it's so common to use, but it has its limitations for sure. To understand its limitations, you need to understand the technique, see for example this explanation.

In essence, I think your problem is causes by the object that cast shadow and the object that receives shadow are closer than the threshold that we use to determine if there should be a shadow. Also, we need that threshold to be well above 0 to avoid numerical issues. Maybe if you generate a shadow map around a smaller target or at a different angle, it will not show?

[huand]

thx for the article, it seems like a peter panning artifact

[asny]

I think you're exactly right 🙂 I guess we could expose an option to render the shadow map with front face culling, but I'm not sure it will help you since it will only work for solid objects?

[huand]

Yes this solution would not do it for me (but maybe useful for others?) Anyway I was just curious about this, but don't really need optical physical accuracy on the shadow, i just use it as a bonus to give a general sense of perspective to the observer, and it fills this need ( the image example I gave are only for some specific angles with the light). But it's good to know where it comes from and understand it!