Initial commit: Vertical Partition Streaming plugin (UE 5.7)

Bounded vertical route partition / streaming for handcrafted spiral climb maps
(Only Up / Only Climb). Not World Partition, not Level Instances as core arch.

- Z-cell segmentation + optional XY subcells, editor builder + commandlet
- NonDestructive visibility backend + streaming-level backend
- Offline HLOD proxies: MergedMesh / SimplifiedProxy (ProxyLOD)
- Universal Level Instance + Packed Level Actor + HISM support (flatten+merge)
- Vertical-aware runtime streamer (full/preload/HLOD/unload, hysteresis,
  velocity prediction, fall-risk), WP-style debug viz + vp.* console
- Safe-by-default: only static decor streams; sky/lights/gameplay stay persistent

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Source/VerticalPartition/Public/VerticalPartitionStatics.h

@@ -0,0 +1,71 @@
+// Copyright IHY. Vertical Partition Streaming plugin.
+//
+// Pure cell math shared by the editor builder and the runtime streamer. No state.
+#pragma once
+
+#include "CoreMinimal.h"
+#include "Kismet/BlueprintFunctionLibrary.h"
+#include "VerticalPartitionTypes.h"
+#include "VerticalPartitionStatics.generated.h"
+
+/** Context the desired-state policy needs beyond the raw cell index. */
+struct FVerticalStreamingContext
+{
+	int32 PlayerCellZ = 0;
+	int32 PlayerCellX = 0;
+	int32 PlayerCellY = 0;
+	float PlayerVelocityZ = 0.f;   // cm/s, +up
+	float PlayerWorldZ = 0.f;      // cm, exact (for hysteresis at boundaries)
+	float CameraPitchDeg = 0.f;    // +looking up
+	bool bUseXY = false;
+};
+
+UCLASS()
+class VERTICALPARTITION_API UVerticalPartitionStatics : public UBlueprintFunctionLibrary
+{
+	GENERATED_BODY()
+
+public:
+	/** Z index of a world Z (cm) relative to the volume floor. */
+	UFUNCTION(BlueprintPure, Category="VerticalPartition")
+	static int32 GetCellZFromWorldZ(float WorldZ, float VolumeMinZ, float CellHeight);
+
+	UFUNCTION(BlueprintPure, Category="VerticalPartition")
+	static int32 GetCellXFromWorldX(float WorldX, float VolumeMinX, float XYCellSize);
+	UFUNCTION(BlueprintPure, Category="VerticalPartition")
+	static int32 GetCellYFromWorldY(float WorldY, float VolumeMinY, float XYCellSize);
+
+	/** Cell id for a single point (actor origin). */
+	static FVerticalCellId GetCellIdFromPoint(const FVector& Point, const FBox& VolumeBounds, const FVerticalPartitionSettings& S);
+
+	/** Cell id for a bounds box. Uses the dominant-overlap cell (center of the
+	 *  clamped intersection) so a box straddling a boundary lands deterministically.
+	 *  bOutCrossesMultiple reports whether the box spans more than one cell. */
+	static FVerticalCellId GetCellIdFromBounds(const FBox& ActorBounds, const FBox& VolumeBounds, const FVerticalPartitionSettings& S, bool& bOutCrossesMultiple);
+
+	/** World-space bounds of a cell, clamped to the volume when requested. */
+	static FBox GetCellBounds(const FVerticalCellId& Cell, const FBox& VolumeBounds, const FVerticalPartitionSettings& S);
+
+	/** Number of Z cells the volume spans (>=1). */
+	static int32 GetNumZCells(const FBox& VolumeBounds, const FVerticalPartitionSettings& S);
+
+	/** THE policy. Maps a cell relative to the player to its desired representation,
+	 *  honouring full/preload/HLOD/unload bands, hysteresis, velocity prediction,
+	 *  fall-risk-below, camera direction and the above-player priority bias.
+	 *  CurrentState is the cell's live state and is what makes hysteresis sticky. */
+	static EVerticalCellDesiredState GetDesiredStateForCell(
+		const FVerticalCellId& Cell,
+		const FVerticalStreamingContext& Ctx,
+		const FVerticalPartitionSettings& S,
+		EVerticalCellState CurrentState = EVerticalCellState::Unloaded);
+
+	/** True when a cell sits in the preload band (load full data, keep it hidden). */
+	static bool ShouldPreloadFull(const FVerticalCellId& Cell, const FVerticalStreamingContext& Ctx, const FVerticalPartitionSettings& S);
+
+	/** Human-readable colour for a runtime state (debug draw / overlay). */
+	UFUNCTION(BlueprintPure, Category="VerticalPartition")
+	static FLinearColor GetStateColor(EVerticalCellState State);
+
+	UFUNCTION(BlueprintPure, Category="VerticalPartition")
+	static FString WarningTypeToString(EVerticalWarningType Type);
+};