[UE4]Shadows

keywords：UE4, Shadow Optimization, Scene Optimization, 阴影, 场景, 优化

Shadow Optimization

Enable Dynamic Shadow Distance

Testing Case: 500 Actors are rendering in screen, Camera height is 4000, DirectionalLight’s property Dynamic Shadow Distance StationaryLight (Default value is 0, which means disabled) should be larger than the straight-line distance from Camera to Actor (Beacause the distance need to cover all Actors, so the distance would be better be larger ), otherwise frame rate would drop down from 200 fps to 100 fps.

How to Cast Shadow by Camera Distance

Tow factors

RayTraced Distance Field Soft Shadows
Scalability of Shadow

RayTraced Distance Field Soft Shadows

Project Settings -> Engine -> Rendering -> Lighting -> enable Generate Mesh Distance Fields (Need to restart Editor)
Modify DirectionalLight’s properties: DistanceField Shadow Distance and RayTraced DistanceField Shadows

Effect

Relationship between DistanceField Shadow Distance & Dynamic Shadow Distance

Stationary
Moveable

Reference:RayTraced Distance Field Soft Shadows
https://docs.unrealengine.com/en-us/Engine/Rendering/LightingAndShadows/RayTracedDistanceFieldShadowing

Scalability of Shadow

Cinematic
Medium
Low

Scalability Reference
https://docs.unrealengine.com/en-US/engine/performance/scalability/scalabilityreference

Cast shadow by level of detail (LOD)

Console command:

//LOD level to force for the shadow map generation only, -1 is off.
r.ForceLODShadow

It works only for non-dynamic lights.

ShadowMap Memory Size

Testing case:
Place 1024 cubes in an empty level, casting shadow by stationary DirectionalLight, and check the memory cost of shadow map. (console cmd:stat rhi)

Shadows quality: Low

Shadows quality: Cinematic

Conclusion:
The higher the shadow quality, the larger the light map resolution, and the larger the memory cost of shadow map .

How to cast character shadow on mobile device

1st way: Movable Directional Light

How to Enable Dynamic Shadows & Correct Reflection Maps on Mobile
https://forums.unrealengine.com/development-discussion/android-development/41661-tip-how-to-enable-dynamic-shadows-correct-reflection-maps-on-mobile

Lighting for Mobile Platforms
https://docs.unrealengine.com/latest/INT/Platforms/Mobile/Lighting/

4.7 release mobile shadows
https://answers.unrealengine.com/questions/180482/47-release-mobile-shadows.html

2nd way: Stationary Directional Light

Enable Cast Modulated Shadows:

Casting Shadow (Common questions)

How to Cast Shadow for SkeletalMesh

Constructor:

UPrimitiveComponent->CastShadow = true;

Run-time:

UPrimitiveComponent->SetCastShadow(true);

UPrimitiveComponent->CastShadow = true; would not work out of Constructor.

How to cast shadow when Actor hidden in game

USkeletalMeshComponent->SetHiddenInGame(true);
USkeletalMeshComponent->bCastHiddenShadow = true;

How to prevent mesh from receiving shadows

Set material’s Shading Model to Unlit, then set you base color to go to the emissive(so its not totally black).But Matellic and Specular would lost.

Reference
https://answers.unrealengine.com/questions/258748/how-to-disable-receiving-shadows-on-a-particular-m.html