35a58670d0b0278e3454a2cadbc0e60ee4b0d23f
3 Commits
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cf930f68bb
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Add a second partitioner, so the vtable is a seam and not a decoration
A binary space partition on libakstdlib's tree links and lists, registered in the factory as "bsp". It runs the same assertions the grid does, because tests/partition.c is a table over partitioners and adding a row is all it takes to be held to the contract. **Use the grid.** This is here to prove the vtable works and to have something to measure the grid against, and the file says so at the top. It rebuilds whenever the proxy set changes, which is the shape PERFORMANCE.md records Phaser using and capping out around five thousand bodies. It would earn its place in a world with wildly non-uniform object sizes, or one larger than the grid's fixed cell array covers. The difference is visible in the code rather than buried in a benchmark: the grid's `move` compares four integers and returns when a proxy has not left its cells, and this one marks the whole partition stale. The incremental-move assertion in the suite is therefore grid-only, and says why. aksl_tree_iterate is not used, and the file carries the three reasons so the next reader does not rediscover them: it is a complete traversal whose only control signal stops the entire walk, so there is no way to prune a subtree -- which is the only operation a spatial query is made of; it carries no per-node context, and a pruning descent needs each node's bounds and plane; and its breadth-first modes allocate, while only the depth-first ones are malloc-free and those are the ones without pruning. aksl_tree_insert is unusable for a different reason again: it is a comparator-ordered BST, and a spatial insert has to compare a leaf against a plane, which aksl_TreeCompareFunc cannot express. What is used is the link structure and the lists, neither of which allocates, which is why they fit here at all. The descent is an explicit stack rather than recursion, so the depth bound is an array bound the compiler can see -- this library already has one documented way to blow the C stack and does not need a second. Split planes are the median of the item centres on the longer axis, not the spatial midpoint: actors in a tile game cluster on the floor, and a midpoint split gives one empty child and one full one for several levels running. A split that separates nothing degrades the node to a leaf rather than recursing forever on the same set. Co-Authored-By: Claude Code <noreply@anthropic.com> Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> |
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e632abf720
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Let a map say which layers are solid, and answer questions about them
A tile layer with a `collidable` boolean custom property is collision geometry. Before this a game had to hard-code a layer index -- both examples do, because akgl_TilemapLayer does not retain the name Tiled wrote -- and that index changes the moment somebody reorders layers in the editor. Solid tiles are **not** given proxies. At the maximum map size that is a quarter of a million per layer, tens of megabytes of index to describe data that is already a dense grid sitting in the tilemap. The world keeps a borrowed pointer and reads layers[i].data[] over whatever cell range a query covers: nine array reads for a 32-pixel actor on 16-pixel tiles, nothing to build at level load, and nothing to maintain per frame. Static geometry that is not tile-aligned is still an ordinary proxy with AKGL_COLLISION_FLAG_STATIC; both mechanisms exist and tiles use the free one because there are a hundred thousand of them. Four public queries come with it, all of which answer without resolving: solid_at, box_blocked, query_box and settle. They are what a game reaches for when it wants to know rather than to be pushed -- a ledge probe ahead of a walking enemy, a check that a doorway is clear -- and the sidescroller cannot drop its hand-rolled collision without them. akgl_collision_settle is the one worth naming. Resolution stops a shape entering geometry and has nothing to say about one that began inside it: what it does instead is refuse every move, so an actor spawned in a wall is simply stuck. Level authors produce that constantly, so settling walks a shape up a tile at a time and refuses loudly rather than searching forever. Two defects found by writing the tests: - The fixture put an akgl_Tilemap on the stack and segfaulted before the first assertion. It is about 26 MB -- the layer and tileset arrays are sized for the worst case the format allows -- and tilemap.h says so. It is static now, with a comment saying why, because the next person to write a map fixture will reach for a local first as well. - The far-edge nudge used AKGL_COLLISION_EPSILON, which is 1e-6. That is a sensible tolerance on a unit vector and a meaningless one on a map coordinate: `float` carries about seven significant digits, so at a coordinate of 144 the smallest representable step is around 1.5e-5 and `144.0f - 1e-6f` is exactly 144.0f. The nudge did nothing, a box resting flush on the floor read as inside it, and every move it tried looked blocked -- an actor standing on the ground unable to walk. Two different quantities were sharing one constant; the tile one is now its own, at a thousandth of a pixel, which is what the sidescroller example independently arrived at. Both breaks verified: removing the nudge and ignoring the `collidable` bit each turn the suite red with the symptom named. Co-Authored-By: Claude Code <noreply@anthropic.com> Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> |
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68e042bd47
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Add a pluggable broad phase, and the incremental uniform grid behind it
akgl_Partitioner is a record of function pointers and an initializer, the same shape as the render and physics backends. `move` is its own slot rather than remove-then-insert, and that is the whole design: a uniform grid's move is a comparison and a return when the proxy has not left the cells it was in, which is the steady state for a walking actor and the permanent state for a static one. Spelling it as remove-and-insert would turn the incremental grid into the rebuild-every-frame tree that PERFORMANCE.md already measured and rejected. The grid is a dense 128x128 array of cell heads over the world, cells keyed on tile size, with two intrusive chains per entry -- one through the cell so a query can walk it, one through the proxy so removal unlinks a whole span without searching. Everything is an int16_t index rather than a pointer, so the structure is relocatable and clearing it is a memset. A proxy covering more cells than AKGL_COLLISION_GRID_MAX_SPAN spills onto one chain every query walks, which is what makes the cell pool's ceiling provable rather than hopeful. tests/partition.c compares every query against a linear scan over the same proxies and asserts containment in one direction, not equality. That asymmetry is the contract: over-reporting costs a narrowphase call, under-reporting is a wall an actor walks through. The suite is a table over partitioners so the same assertions run against every implementation, which is what the second one landing later will be held to. Three deliberate breaks, and two of them were not caught the first time: - Removing the min-cell rule so a shared-cell pair reports repeatedly: caught. - Dropping the unlink in `move`: **not caught**, initially. Stale entries do not produce wrong query answers, because the bounds re-check filters them out -- they leak the cell pool until the grid stops working, on a timescale no unit test reaches by accident. Counting live pool entries across 200 moves is the only thing that sees it, and now does: 505 entries against an expected 5. - Swapping floorf for a truncating cast: **not caught, and correctly so.** Everything below zero is clamped to cell 0 either way, so today the two are indistinguishable. The comment claiming truncation is a defect was overstating it and now says what is actually true: the clamp is the only thing hiding it, and a negative world origin or a relaxed clamp would make it real with no test standing in front of it. Co-Authored-By: Claude Code <noreply@anthropic.com> Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> |
