ALCCClippingVolume: 3DGS Clipping Volume

Clipping volume Actor that clips away part of an LCC scene with a box or sphere volume.

#include "Tools/LCCClippingVolume.h"

For the usage steps, a demonstration, and the property panel description, see Scene Editing - Clipping Volumes. This page only lists the interfaces.

Properties

For the meaning of the values see EClipType and EClipVolumeType.

None of the three properties has a Setter, and an assignment at runtime requires a call to Refresh to take effect. The same applies to a transform change at runtime.

Methods

SetUpdateComponent

UFUNCTION(BlueprintCallable, Category = "XGrids")
void SetUpdateComponent(ULCCComponentBase* Component);

Binds the LCC Component to update.

Refresh() needs this binding to take effect, since internally it marks the bound Component as needing its render state rebuilt. Without a binding, Refresh() triggers no render update.

Adding a volume with AddClippingVolume usually establishes the association already; when a change to a clipping volume created dynamically at runtime has no effect, check whether this method was called first.

Refresh

UFUNCTION(BlueprintCallable, Category = "XGrids")
void Refresh();

Triggers one update of the clipping result manually; internally it marks the bound LCC Component as needing its render state rebuilt.

A call is required after changing a clipping volume at runtime for the change to take effect, including:

• Property changes: bEnabled, Mode, VolumeType. These properties have no Setter, and a direct assignment does not notify the rendering side.
• Transform changes: SetActorLocation, SetActorRotation, SetActorScale3D.

Automatic updates only happen in the editor: property changes in the Details panel go through PostEditChangeProperty, and dragging the gizmo goes through functions such as EditorApplyTranslation. Those paths are all under WITH_EDITOR and do not exist at runtime.

It requires SetUpdateComponent to have been called, or the association to have been established through AddClippingVolume. No render update is triggered while no Component is bound.

When changing several clipping volumes at once, call Refresh() on each one after its properties are changed.

Runtime Creation

#include "Tools/LCCClippingVolume.h"
#include "LCCComponentBase.h"

ALCCClippingVolume* AMyTool::CreateBoxClip(
    ULCCComponentBase* Component, const FVector& Location, const FVector& Extent)
{
    ALCCClippingVolume* Volume = GetWorld()->SpawnActor<ALCCClippingVolume>(
        ALCCClippingVolume::StaticClass(), Location, FRotator::ZeroRotator);
    if (!Volume)
    {
        return nullptr;
    }

    Volume->VolumeType = EClipVolumeType::Box;
    Volume->Mode = EClipType::Inside;
    Volume->bEnabled = true;

    // the size of an AVolume is controlled through scaling
    Volume->SetActorScale3D(Extent / 100.0f);

    Volume->SetUpdateComponent(Component);
    Component->AddClippingVolume(Volume);

    return Volume;
}

To toggle the clipping effect temporarily, do not add and remove array elements; changing bEnabled is lighter. Remember to call Refresh() after the change:

for (ALCCClippingVolume* Volume : MyVolumes)
{
    if (Volume)
    {
        Volume->bEnabled = bEnable;
        Volume->Refresh();
    }
}

Moving a clipping volume at runtime for an animation also requires a refresh every time:

// sweep the clipping volume across the scene
FVector Loc = ClipVolume->GetActorLocation();
Loc.X += 200.0f * DeltaTime;
ClipVolume->SetActorLocation(Loc);
ClipVolume->Refresh();          // runtime transform changes do not update automatically

For the Blueprint nodes see Scene Editing - Blueprint Methods.

Notes

• Clipping only affects rendering, not collision. A clipped-away area can still be hit by a ray and still blocks a character.
• Several clipping volumes acting at once are evaluated independently and their effects stack. Mixing Inside and Outside easily produces unexpected results.
• The number of clipping volumes in effect at once is limited, to 50 without a license; the extras do not take part in rendering and a warning is logged. Clipping volumes and section planes share this quota. For licensing see Editions and Licensing.
• Destroying a clipping volume only triggers one render update and does not remove the element from the ClippingVolumes array of the Component, leaving a stale pointer in the array (skipped automatically during rendering). To keep the array clean, call RemoveClippingVolume before destroying.

See Also

• Scene Editing: full usage description
• ALCCSectionPlane: sectioning with a plane
• ULCCComponentBase: AddClippingVolume and RemoveClippingVolume