ludic/packages/ludic.physics

ludic.physics

Rigid bodies, still shapes that can be removed, queries and buoyancy, over Jolt Physics (MIT) built here from a pinned tag (phase 16). Uses ludic.base and nothing else.

import "ludic.physics"

The rules it keeps

• A package with a native library (phase 15): native/build.sh fetches Jolt v5.6.0, checks its SHA-256, and builds it with the shim native/shim/jph_shim.cpp into lib/<target>/ (libludicjolt.dylib, ludicjolt.dll). The shim keeps the rules in packages/README.md: no callback into Ludic, contacts recorded during the step and drained after it, Jolt's job threads inside C.
• Deterministic across machines: JPH_CROSS_PLATFORM_DETERMINISTIC and no floating point contraction, so the Mac and the PC agree in co-op and a run repeats to the bit (a test holds it).
• Fixed steps: phys_tick runs as many 1/60 s steps as the frame's time holds, at most four - frame rate never changes the rules, and a stall is not replayed.
• It saves nothing. A thing at rest is saved by the Thing's owner; the world is rebuilt on load and on a map swap (phys_close, phys_open).
• A shape and the world are handles it keeps; a game names a shape and a body by an int.
• Removal is real: phys_remove takes a body out of the world - no parking it far away.

The API

phys_open(st, max_bodies, threads) -> bool, phys_close(st), phys_is_open(st)	a world, and everything in it let go
phys_box, phys_sphere, phys_capsule, phys_cylinder, phys_dome(r, h), phys_offset(shape, x, y, z, yaw)	shapes, each an int (-1 refused); a dome is a boulder standing on its origin
phys_heightfield(st, h, n, ox, oz, cell), phys_mesh(st, v, nv, tri, nt)	the ground (PHYS_HOLE is none) and a dock or cabin
phys_ground_add, phys_static_add, phys_kinematic_add, phys_body_add(..., mass)	bodies: the ground, still things, what the game moves (the player), what falls and floats
phys_settle(st)	after adding many still things, before the first query
phys_remove(st, id), phys_count(st)	gone for good
phys_pose(st, id) -> PhysPose, phys_yaw_of(p)	position, rotation, velocity
phys_place, phys_impulse, phys_set_velocity, phys_set_kinematic_target, phys_awake	moving a body
phys_ray(st, o, d, mask) -> PhysHit	the first thing along a ray
phys_top_at(st, x, z, r, from_y, depth, mask) -> float	what a foot would land on (CharacterGround.top_at), PHYS_NONE if nothing
phys_push(st, x, z, r, y0, y1, mask) -> PhysPush	the move that stands an upright body clear (CharacterGround.push)
phys_overlap(st, x, y, z, r, mask) -> []int	the bodies a ball touches
phys_float(st, id, buoyancy, linear_drag, angular_drag), phys_sink, phys_floating	a body buoyed each step against PhysWater and carried by its current
phys_facts(st)	PhysFact: PHYS_HIT (two bodies met at ph_hard m/s or more), PHYS_SPLASH (a floating body reached water)
phys_tick, phys_advance(st, dt) -> steps, phys_step, phys_system()	the system, in PH_SIMULATE
phys_config(st, step, sub, hard), phys_gravity(st, y)	the numbers

A query's mask is PHYS_M_GROUND, PHYS_M_STATIC, PHYS_M_MOVING, or PHYS_M_SOLID / PHYS_M_ALL - the body's own questions leave the ground out, because hk_ground stays the pure ground query.

The port

PhysWater { height(x, z), current_x(x, z), current_z(x, z) } - the surface under a point (PHYS_NONE where there is no water) and the current there. Unbound, there is no water. The game binds it to the same function its water is drawn with, so a boat never floats on a different wave from the one on screen.

Tests

ludic test packages/ludic.physics runs the real library: a box onto a heightfield and a ray to it, still things removed, a boulder's top, a push out of a post, a crate floating level and drifting, hard and soft landings, a kinematic shove, fixed steps, and a pile run twice to the bit.