Unity shadow shadow pancaking

Shadow Pendant （Shadow pancaking）

To reduce shadow and dark spots （Shadow acne）Unity Adopted a method called Shadow flat falling （Shadow pancaking） Technology , The idea is to reduce the range of lighting space used when rendering shadow maps along the lighting direction , This can improve the accuracy of shadow mapping , Reduce shadows and dark spots （Shadow acne）

As shown in the figure below , It mainly takes the intersection between the light direction and the visual cone
Light blue circles indicate objects that produce shadow casting
The dark blue rectangle represents the original light space
The green line indicates the optimized near plane , Eliminate all invisible shadow casting objects that are not visible cones

It looks like , Equal to that we truncate the shadow casting objects within the optimized light near the clipping plane （ At the top Shader in ）, It should be noted that although the performance is generally ok , However, problems arise when you encounter some particularly large triangular surfaces that span this near clipping plane .

As shown in the figure above , Only one vertex of the blue triangle is outside the near clipping plane , And cut off , So there's a problem , Will change the shape of the triangle , Produce false shadows .

We can adjust Unity In the quality settings Shadow Near Plane Offset To solve this problem , Let the near clipping plane of light space move back , However, if this value is set high, it will cause shadow dark spots （Shadow acne）, Because it also increases the space of the light direction corresponding to the shadow map . Or we can solve this problem by subdividing the large triangular surface .

Reference resources

https://docs.unity3d.com/2019.4/Documentation/Manual/ShadowPerformance.html