6e97d27e49533c371d55008ff56383ca7e06dd16
4 Commits
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a8526ad55e
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Give an actor a say in how it answers a collision
A seventh behaviour hook, collidefunc, defaulting to akgl_actor_collide_block. Contacts are delivered one actor at a time with the normal already pointing the way that actor has to move, which removes the "which one is a1" ambiguity that made the old physics `collide` slot unimplementable -- and means a game overriding one actor's response never has to reason about the other's. The default moves the actor out along the normal by the penetration depth and removes the component of its motion that was going into the surface. Three things about that are easy to write wrongly, and each has a test that names the symptom rather than the assertion: - **It writes `e` and `t`, never `v`.** akgl_physics_simulate recomputes velocity as `e + t` at the top of every step, so a write to `v` is discarded before anything reads it. Worse than useless: an actor holding a direction into a wall would keep accumulating thrust while standing still and leave at speed the instant the wall ended. Breaking this leaves the fall running at 300 px/s through the floor. - **It removes the component, not the axis.** Zeroing the whole thrust vector costs the actor its motion *along* the surface as well, which is a character scraping a ceiling stopping dead and a character landing on a floor losing its run. Sliding along a wall is the difference between a wall and glue. - **A separating contact is left alone.** An actor already moving out of a surface that gets its velocity zeroed is an actor stuck to a wall it is walking away from, and it reads to a player as the collision grabbing them. `e` and `t` are treated separately rather than as their sum, so an actor pressing into a floor loses its downward gravity without losing the sideways run it is also doing. A sensor is reported and never pushed -- walking through a coin is not being blocked by it. The default deliberately does not pre-load the environmental term with a step of gravity. A resolver running *before* the step has to, or the step it is correcting for re-adds gravity and commits a quarter pixel of penetration, which is invisible and still fatal because every horizontal move then reads as blocked. This library resolves after the move, so the case does not arise; the sidescroller example carries that workaround because it had no choice. Also asserted: the other six hooks survive. A seventh that displaced one of them would be a silent regression somewhere unrelated. Co-Authored-By: Claude Code <noreply@anthropic.com> Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> |
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a3cb6ca79a
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Answer whether two shapes overlap, and how to undo it
akgl_collision_test takes two proxies and fills in a contact: a unit normal, a depth, and a point. Three paths, cheapest first. The proxies' bounds reject most pairs in four comparisons and no arithmetic, which is free because the bounds were computed when the proxy was synced. A box against a box is answered in closed form. That is not only cheaper than the general solver, it is *exact*, and the difference shows up where it matters most: an actor resting on a floor wants a normal of precisely (0, -1, 0), and an iterative solver converges to something like (0.0001, -0.99999, 0), which accumulates into a slow sideways creep. A tile game is almost entirely boxes, so this is the path that runs. Everything else goes to ccdMPRPenetration. MPR rather than GJK+EPA because MPR allocates nothing at all, converges in fewer iterations, and its one weakness -- a coarser contact *point* -- is on a field the blocking resolver never reads. EPA stays compiled and available behind the arena for a caller who one day wants an accurate manifold. The header says the point is approximate so nobody builds a damage falloff on it. The normal points out of the second shape and toward the first, so a caller moving `a` along it by `depth` separates the pair. libccd hands back the opposite convention; converting once here saves every resolver from remembering the sign, and getting it backwards would compile, would pass any "do these collide" test, and would drag actors into walls. There is a test that asserts the direction, and inverting the conversion turns it red. AKGL_COLLISION_TEST_PLANAR flattens the normal into the xy plane. The extrusion the setters apply already makes z the most expensive axis, so this is a net for a caller who set a depth by hand -- and the failure it catches is silent: the narrowphase reports a contact, the resolver pushes the actor into the screen, and the actor does not move on screen while remaining inside the floor. It also rescues the degenerate case, two shapes at exactly the same centre, where there is no planar direction at all and a zero-length normal would be a wall that stops nothing. Level authors stack things constantly. Three things the tests found rather than assumed: - The guard has two copies, one per path, and the box one is where it earns its place. Removing both is caught; removing only the iterative one is not, because the iterative solver is seeded from the line between the two centres and so converges to a planar answer on its own for a planar offset. That is measured and written down in the test rather than papered over with a fixture contrived to force it. - A concentric pair has no preferred sign on the degenerate axis, so the test asserts the magnitude of the normal rather than its direction. The first version asserted -1 and failed against an equally correct +1. - The box fast path and the iterative solver are two implementations of one answer, so they are driven over the same arrangements and required to agree on the decision and the axis. A shortcut nothing cross-checks is a shortcut waiting to diverge. Co-Authored-By: Claude Code <noreply@anthropic.com> Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> |
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d0b057f47a
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Pool collision proxies, and tie one to the life of its actor
A proxy is what the broad phase will index: an actor's shape, where it is, and the bounds that follow from those. It is a sixth heap layer, two per actor -- one for the actor itself and headroom for static geometry a game registers that is not tile-aligned. Solid *tiles* deliberately get none: the broad phase will read those out of the tilemap's own array, because one proxy per tile is tens of megabytes to index data that is already a grid. The pool follows the existing convention rather than improving on it. akgl_heap_next_collision_proxy finds a free slot and does not claim it; akgl_collision_proxy_initialize claims it. That is TODO.md item 8's asymmetry, and it is kept on purpose: an acquire abandoned before initialization leaks nothing, because the slot still reads as free, and a sixth pool with its own rule would be worse than one defect with five instances. Fixing item 8 means fixing all five together with every call site audited, and that is its own change. The proxy holds a *copy* of the shape rather than a pointer. An actor's own logic may rewrite its shape mid-step -- a character crouching, a projectile arming -- and a broad phase whose bounds came from a shape that has since changed is a bug that only appears when two things happen in the same frame. akgl_heap_release_actor now releases the actor's proxy. Without it the proxy holds a borrowed `owner` into a slot that has just been zeroed, so the broad phase keeps a registration whose owner reads as a free actor, and the next contact against it is a collision with nothing. Verified by removing the release and watching test_proxy_dies_with_its_actor go red. The tests pin the convention as well as the behaviour: that two acquires with no initialize between them return the same slot is asserted, not merely tolerated, so that changing the convention has to change a test that says why it exists. Co-Authored-By: Claude Code <noreply@anthropic.com> Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> |
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9056ff06d6
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Add collision shapes, on the character and overridable per actor
A shape is a convex volume positioned relative to an actor's origin. It lives on akgl_Character, so every goblin sharing a character shares one shape definition the way they already share speeds and the state-to-sprite map, and an actor may override it with akgl_Actor::shape_override. The flag is not redundant with an empty shape. "This actor deliberately has no collider" and "this actor has not been given one yet" are different states, and without somewhere to record the difference akgl_actor_set_character cannot tell whether it is allowed to overwrite what it finds. include/akgl/collision.h is a leaf: it names actors and tilemaps as incomplete struct pointers rather than including their headers, because both of those need akgl_CollisionShape by value and a cycle forms otherwise. The `headers` suite compiles it as the first include of a translation unit, so that property is enforced rather than merely intended -- which is why the tilemap types got struct tags two commits ago. The masks are asymmetric and the defaults are the load-bearing part: layermask ACTOR, collidemask STATIC. An actor given a shape and nothing else collides with map geometry and with no other actor. "Everything with a hitbox shoves everything else" would be a surprising default for a town full of scenery and a painful one to discover after the fact; opting in to actor-versus-actor is one bit, opting out of it would have been a hunt through every NPC a game spawns. Every shape gets a z depth, because the narrowphase behind this is three dimensional and answers with the *minimum* separating translation. A thin extrusion makes z the cheapest axis, and an actor pushed along z goes nowhere a player can see while remaining inside the floor -- a collision system reporting success while doing nothing. The ratio of 2 is the smallest for which the z overlap of any two shapes the setters build provably exceeds any planar penetration they can reach. The test for that asserts the inequality across a spread of sizes rather than asserting the constant is 2, so a change to the constant fails here rather than in a game. Two things about that test are worth recording, because the first version had both: - It could not fail. TEST_ASSERT expands to FAIL_BREAK, which reports by `break`ing, and the assertion was inside a nested `for` -- so the break left the loop rather than the ATTEMPT block and the failure evaporated. This is the hazard AGENTS.md documents for CATCH; it applies to the whole family. Verified by setting the ratio to 0.5 and watching the suite still pass, then fixing it and watching it report the 512x512 case by name. - tests/collision_arena.c had the same bug in a loop added in the previous commit, and it is fixed here too. Co-Authored-By: Claude Code <noreply@anthropic.com> Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> |
