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UE3 Home > Unreal Development Kit Gems > Rendering Occluded Actors
UE3 Home > Materials & Textures > Rendering Occluded Actors

Rendering Occluded Actors

Last tested against UDK Mar, 2011
PC compatible

Rendering Occluded Actors

Overview

In third person games, sometimes it can visually appealing to block the player's view with something interesting. However, this can lead to problems when the player actually needs to be able to view through the blocking pixels. This gem demonstrates a simple, performance friendly method to render occluded actors.

Material

This method uses depth checking to alter the opacity of the foreground rendered mesh. To clarify here is the list of steps that the rendering pipeline does.

Render the actor's mesh as per normal
Render an occluded version of the actor's mesh on top; for each pixel
1. Check the new pixel depth against the existing pixel depth
2. If the difference in depth is above a value, then continue to render the occluded pixel
3. Otherwise do not render the pixel

Material properties

In order to have access to the Scene Depth node in the material, the material must be Translucent. Set the material to Unlit to help with performance.

Example

This is an example of how to add the occlusion effect to a pawn. This can of course be used for other actors such as Static mesh actors. The only condition is that the occluded mesh must match the normally visible mesh in terms of location, rotation and scale.

OccludedPawn.uc

class OccludedPawn extends UTPawn;

var(Pawn) const SkeletalMeshComponent OccludedMesh;

simulated function SetMeshVisibility(bool bVisible)
{
  Super.SetMeshVisibility(bVisible);

  if (OccludedMesh != None)
  {
    OccludedMesh.SetOwnerNoSee(!bVisible);
  }
}

simulated function SetCharacterMeshInfo(SkeletalMesh SkelMesh, MaterialInterface HeadMaterial, MaterialInterface BodyMaterial)
{
  Super.SetCharacterMeshInfo(SkelMesh, HeadMaterial, BodyMaterial);

  if (OccludedMesh != None)
  {
    OccludedMesh.SetSkeletalMesh(SkelMesh);
  }
}

defaultproperties
{
  Begin Object Class=SkeletalMeshComponent Name=OPawnSkeletalMeshComponent
    Materials(0)=Material'OccludedPawnContent.OccludedMaterial'
    Materials(1)=Material'OccludedPawnContent.OccludedMaterial'
    DepthPriorityGroup=SDPG_Foreground // Render the occluded skeletal mesh in the foreground layer
    ShadowParent=WPawnSkeletalMeshComponent
    ParentAnimComponent=WPawnSkeletalMeshComponent
    bCacheAnimSequenceNodes=false
    AlwaysLoadOnClient=true
    AlwaysLoadOnServer=true
    bOwnerNoSee=true
    CastShadow=false // Casting shadows is not required
    BlockRigidBody=true
    bUpdateSkelWhenNotRendered=false
    bIgnoreControllersWhenNotRendered=true
    bUpdateKinematicBonesFromAnimation=true
    bCastDynamicShadow=false // Casting shadows is not required
    RBChannel=RBCC_Untitled3
    RBCollideWithChannels=(Untitled3=true)
    LightEnvironment=MyLightEnvironment
    bOverrideAttachmentOwnerVisibility=true
    bAcceptsDynamicDecals=false
    bHasPhysicsAssetInstance=true
    TickGroup=TG_PreAsyncWork
    MinDistFactorForKinematicUpdate=0.2f
    bChartDistanceFactor=true
    RBDominanceGroup=20
    MotionBlurScale=0.f
    bUseOnePassLightingOnTranslucency=true
    bPerBoneMotionBlur=true
  End Object
  OccludedMesh=OPawnSkeletalMeshComponent
  Components.Add(OPawnSkeletalMeshComponent)

  CamOffset=(X=16.0,Y=64.0,Z=-52.0)
}

This game info subclass is only required to spawn in the OccludedPawn class that was created above.

OccludedGameInfo.uc

class OccludedGameInfo extends UTDeathmatch;

defaultproperties
{
  DefaultPawnClass=class'OccludedPawn'
}

Limitations

A limitation of this method is the way it checks for occlusion. By simply comparing the depth differences and not checking what rendered the pixel, this method can often perform a lot of occlusions incorrectly.

The best way to over come this limitation is to alter the level geometry to ensure that there is a large depth difference potential.

Downloads

Download the source and content used in this gem. (OccludedPawn.zip)