Collision Streaming

PPG generates terrain collision on a planet-wide virtual grid that is independent of the visible terrain quadtree. Every collision cell at the selected grid level has the same effective size and sampling layout. Canonical cube-face cell keys prevent multiple invokers from creating duplicate collision chunks in the same location.

Collision chunks evaluate the same generation material as visible terrain. Active collision invokers and collision-backed navigation coverage request them; chunks are removed after they leave the retained area.

Collision Invokers

Add a PPG Planet Collision Invoker component to characters, vehicles, physics objects, or other actors that require nearby collision. A PPG Navigation Invoker Component also serves as a collision invoker when its generation settings have Independent Navigation Generation disabled. When that setting is enabled, add a separate collision invoker only where physics collision is needed.

Setting	Description	Default
Target Planet	Planet to request collision from. When unset, the component periodically selects the nearest planet surface.	None
Collision Radius	Radius of the requested patch projected onto the planet surface.	10,000 cm
Height Margin	Additional activation height above the resolved local terrain maximum. Negative values are supported.	25,000 cm
Height Deactivation Hysteresis	Extra height retained after activation to prevent rapid enable/disable changes.	10,000 cm
Height Prediction Time	Extends activation using inward radial velocity so fast-descending objects request collision earlier.	1 s
Automatic Planet Search Interval	Interval between nearest-planet searches when Target Planet is unset.	0.5 s

The collision grid recalculates after an invoker moves a fraction of a cell rather than traversing all six cube faces every frame. Invokers above the local terrain maximum plus Height Margin do not request chunks. If local height data is unavailable, the planet-wide height range is used as a fallback.

Assign Target Planet when a level contains multiple nearby planets and automatic selection would be ambiguous.

Planet Spawner Settings

Setting	Description
Generate Collisions	Enables invoker-driven terrain collision generation.
Wait For Initial Collision Before Generation Finished	Delays On Planet Generation Finished until the collision cells requested on the first runtime generation tick are ready.
Match Collision Chunks To Max Recursion Level	Uses the same cell boundaries as visible terrain at Max Recursion Level.
Collision Chunk Size	Requested cell edge size in centimeters when matching is disabled. The value is rounded to the nearest valid power-of-two cube-face subdivision.
Collision Chunk Quality	Collision mesh quads per edge. 0 uses visible Chunk Quality; matching to maximum recursion caps the requested value at visible chunk quality.
Generate Foliage Collision	Generates physics bodies for collision-enabled foliage entries inside collision chunks.
Use Local Collision Height Cutoff	Uses cached collision-cell and nearby visible-terrain height bounds for altitude activation.
Max Cached Collision Cell Heights	Limits retained exact cell-height entries. 0 disables the persistent cache.
Async Init Body	Uses Unreal's asynchronous physics-state pre-registration for foliage collision components where supported.
Max Collision Chunk Generation Starts Per Frame	Limits collision jobs started per frame. Collision shares the global GPU and mesh-build limits.
Debug Draw Collision Chunks	Renders active collision chunks as ordinary Lit meshes.

Matching collision cells to maximum-recursion terrain boundaries is the safest default for consistent sampling alignment. A custom cell size can reduce the number of chunks or tighten streaming coverage, but it is still quantized to the planet's cube-face grid.

Runtime Generation and Loading

Terrain sampling is dispatched to the GPU and read back asynchronously. Collision mesh construction and Chaos triangle-mesh cooking run on background threads. Final Unreal object setup and component registration run on the game thread.

When Wait For Initial Collision Before Generation Finished is enabled, the spawner snapshots the collision cells requested on the first runtime generation tick and retains them until they reach the final READY state. This state includes foliage collision registration when foliage collision is enabled. An empty initial request does not delay the event.

Get Planet Generation Status includes these initial collision cells in completed and total chunk counts. Collision continues to stream around invokers after initial planet loading finishes.

Editor Collision

Generate Editor Collisions generates collision around the active editor viewport camera and placed collision invokers. It is enabled by default. Editor Camera Collision Radius and Editor Camera Height Margin control the camera request.

Hidden collision chunks participate in editor placement traces, so dragged actors and surface snapping can use the generated terrain without rendering the chunks. Enable Debug Draw Collision Chunks when the collision mesh needs to be inspected directly.

Foliage Collision

Foliage collision requires all of the following:

• Generate Collisions on the Planet Spawner
• Generate Foliage Collision on the Planet Spawner
• Enable Collision on the foliage entry
• a positive resolved Collision Range on the foliage entry

Collision foliage uses the base mesh variants rather than distance-based PPG foliage LOD substitutions. It evaluates the same height, slope, vertex-color density mask, alignment, scale, depth-offset, and clustering rules as rendered foliage without distance-LOD thinning. Physics instances are grouped by static mesh into non-rendering instanced components.

Collision Range is measured along the planet surface from an invoker. Range relevance is evaluated per collision cell, so an intersecting cell can contain collision foliage across its complete area. Smaller collision cells provide tighter range boundaries at the cost of more chunks.

When Collision Range remains negative on a serialized asset, PPG derives a centimeter range from its deprecated recursion-distance value. Set an explicit centimeter value when tuning current assets.

Diagnostics and Performance

Show Generation Debug reports:

• active collision chunks
• currently needed collision chunks
• pending needed chunks

Active can temporarily exceed needed because retained cells prevent rapid churn and finished removals can lag behind a changed request. Collision generation starts are limited separately, then share Max Chunk Generation Starts Per Frame, Max Concurrent GPU Generations, and Max Concurrent Mesh Builds with visible terrain.

For lower runtime cost:

• keep invoker radii only as large as gameplay requires
• use explicit Target Planet references when automatic searches are unnecessary
• keep local height cutoffs enabled
• limit foliage Collision Range independently for each entry
• disable foliage collision for decorative meshes
• keep collision debug rendering disabled outside diagnostics