ULineBatchComponent

General usage in the engine

UWorld has 3 line batcher components:

• LineBatcher: “Line Batchers. All lines to be drawn in the world.”
• PersistentLineBatcher: “Persistent Line Batchers. They don’t get flushed every frame”
• ForegroundLineBatcher: “Foreground Line Batchers. This can’t be Persistent.”

There is also a single LineBatcher made in the FPreviewScene.

In DrawDebugHelpers GetDebugLineBatcher is used to get what instance to use. ForegroundLineBatcher is picked if the depth is strictly equal to 1. PersistentLineBatcher is picked if the draw is marked as persistent or the draw time is higher than 0. Otherwise for single frame draws LineBatcher is used.

They are all from the same type, and set up the same.

LineBatcher

• Has bCalculateAccurateBounds set to false.
• Is used by Niagara, HUD, Viewport, WorldPartition, SkeletalMeshComponent

PersistentLineBatcher

• Has bCalculateAccurateBounds set to false
• Is used by DrawPrimitiveDebugger

ForegroundLineBatcher

• Has bCalculateAccurateBounds set to false
• Is used by Viewport, CameraDebugRenderer

Config

• bCalculateAccurateBounds: “Whether to calculate a tight accurate bounds (encompassing all points), or use a giant bounds that is fast to compute.”. This is true by default and is used in ULineBatchComponent::CalcBounds.

Process

On tick the component updates the lifetime of the batched elements and removed expired elements. If at least 1 element was removed MarkRenderStateDirty is called.

Render

• In each DrawXXX function UActorComponent::MarkRenderStateDirty is called.
• FLineBatcherSceneProxy is the proxy scene type of the line batcher component.
• All batches points, lines and meshes has a uint32 BatchID that is set to 0 (INVALID_ID) by default. Use ULineBatchComponent::ClearBatch to clear it.
• FLineBatcherSceneProxy::GetDynamicMeshElements is what draws the points and lines on the PrimitiveDrawInterface.