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Super Mario Galaxy’s defining mechanic — walking on the outside of spherical planets, inside bowls, and along wires — is driven by a gravity subsystem that can blend contributions from any number of overlapping PlanetGravity instances at once. Every frame, PlanetGravityManager::calcTotalGravityVector iterates all registered sources, discards ones that do not cover the querying position, and accumulates a final gravity vector returned to the actor. Because each source carries a priority value, the manager can also report which source dominated, letting actors adjust their orientation, shadow projection, and magnet behaviour accordingly.
The abstract base class for all gravity sources. Stores shared fields such as mRange, mPriority, mGravityType, and mIsInverse. Subclasses override calcOwnGravityVector to describe the field geometry.
ParallelGravity — directional / planar gravity
Produces a uniform directional field aligned to a configurable plane normal. Covers three range shapes: sphere, box, or cylinder. This is what large flat platforms and level-gravity areas use.
class ParallelGravity : public PlanetGravity {public: enum RANGE_TYPE { RangeType_Sphere = 0, RangeType_Box = 1, RangeType_Cylinder = 2 }; enum DISTANCE_CALC_TYPE { DistanceCalcType_Default = -1, DistanceCalcType_X = 0, DistanceCalcType_Y = 1, DistanceCalcType_Z = 2 }; virtual void updateMtx(const TPos3f& rMtx); virtual bool calcOwnGravityVector(TVec3f* pDest, f32* pScalar, const TVec3f& rPosition) const; TVec3f mPlaneUpVec; // local up direction TVec3f mWorldPlaneUpVec; // world-space up direction RANGE_TYPE mRangeType; DISTANCE_CALC_TYPE mDistanceCalcType;};
PointGravity — single-point attraction
Pulls actors toward a single world-space point. Used for small celestial bodies and any scenario where gravity should converge on one location.
Defines a segment between two points. Actors are pulled toward the nearest point on the segment axis, producing a cylindrical gravity field with optional hemispherical caps at each end.
Attracts actors toward the surface of a circular disc. The disc has a configurable radius, a normal direction, and an optional edge-gravity band for actors beyond the rim.
class DiskGravity : public PlanetGravity {public: virtual void updateMtx(const TPos3f& rMtx); virtual bool calcOwnGravityVector(TVec3f* pDest, f32* pScalar, const TVec3f& rPosition) const; TVec3f mLocalNormal; // disc face normal (local) TVec3f mWorldNormal; // disc face normal (world) f32 mLocalRadius; f32 mWorldRadius; f32 mValidDegree; // angular coverage of the field bool mEnableBothSide; // attract from both faces bool mEnableEdgeGravity;};
DiskTorusGravity — torus / ring gravity
Like DiskGravity, but hollowed out into a torus. Actors are attracted toward the nearest point on the ring centerline rather than toward a flat surface centre.
class DiskTorusGravity : public PlanetGravity {public: virtual void updateMtx(const TPos3f& rMtx); virtual bool calcOwnGravityVector(TVec3f* pDest, f32* pScalar, const TVec3f& rPosition) const; TVec3f mLocalPosition; TVec3f mLocalDirection; f32 mRadius; // distance from torus centre to ring centerline f32 mDiskRadius; // cross-section radius s32 mEdgeType; bool mEnableBothSide;};
ConeGravity — cone-shaped field
Pulls actors toward the nearest point on the surface of a cone. The x column of the stored matrix encodes the radius vector, and the y column encodes the axis from base to apex.
class ConeGravity : public PlanetGravity {public: virtual void updateMtx(const TPos3f& rMtx); virtual bool calcOwnGravityVector(TVec3f* pDest, f32* pScalar, const TVec3f& rPosition) const; TPos3f mLocalMtx; // encodes radius (x), axis (y), base position TPos3f mWorldMtx; f32 mWorldRadius; bool mEnableBottom; // include the circular base face f32 mTopCutRate; // truncate the apex by this fraction};
WireGravity — polyline / cable gravity
Attracts actors toward the nearest point along an arbitrary polyline defined by a list of vertices. Used for wire, rope, and cable objects.
PlanetGravityManager is the singleton that owns all active gravity sources for a stage. It is a NameObj and therefore participates in the normal init/movement lifecycle.
class PlanetGravityManager : public NameObj {public: PlanetGravityManager(const char* pName); // Primary query: accumulate gravity from all sources covering rPosition. // gravityType is a bitmask (GRAVITY_TYPE_NORMAL, SHADOW, MAGNET, …). // requester is the calling object pointer; sources whose host == requester // are excluded so objects are not attracted to themselves. bool calcTotalGravityVector(TVec3f* pGravity, GravityInfo* pInfo, const TVec3f& rPosition, u32 gravityType, u32 requester) const; // Register a new PlanetGravity, sorted by priority. void registerGravity(PlanetGravity* pGravity);private: PlanetGravity* mGravities[128]; // registered sources s32 mNumGravities;};
mGravities is a fixed-size array capped at 128 sources. Registering more than 128 gravity objects in one stage is unsupported.
GravityInfo is the result struct filled in by calcTotalGravityVector. Actors store one of these and read it every frame.
class GravityInfo {public: GravityInfo(); void init(); TVec3f mGravityVector; // normalised accumulated direction s32 mLargestPriority; // priority of the dominant source PlanetGravity* mGravityInstance; // pointer to the dominant source};
