libakgl/include/akgl/heap.h

/**
 * @file heap.h
 * @brief The object pools. This library does not call `malloc`, it claims slots.
 *
 * Every runtime object -- actors, sprites, spritesheets, characters, strings --
 * comes out of a fixed, statically allocated array declared here. A "heap layer"
 * is one such array plus its `next`/`release` pair. Allocation is a linear scan
 * for a slot whose `refcount` is 0; release decrements, and the slot is zeroed
 * and unregistered when the count reaches 0.
 *
 * The consequence to design around is that exhaustion is a *normal* error, not
 * an out-of-memory catastrophe: AKGL_ERR_HEAP means the pool is full, and the
 * fix is usually a missing release rather than a bigger pool. Every ceiling
 * below is overridable at compile time, so a game that needs 256 actors defines
 * `AKGL_MAX_HEAP_ACTOR` before including this -- but the arrays are sized at
 * compile time, so the library and everything linking it must agree.
 *
 * If you need a new kind of runtime object, add a layer here. Do not reach for
 * the allocator.
 *
 * @warning The acquire functions are asymmetric: akgl_heap_next_string takes the
 *          reference for you, and the other four do not -- their caller is
 *          expected to take it, which in practice the `*_initialize` function
 *          does. Until one is taken the slot is still free and the next
 *          allocation hands out the same pointer. TODO.md, "Known and still
 *          open" item 8.
 */

#ifndef _AKGL_HEAP_H_
#define _AKGL_HEAP_H_

#include <akgl/sprite.h>
#include <akgl/actor.h>
#include <akgl/character.h>
#include <akgl/staticstring.h>
#include <akerror.h>

#ifndef AKGL_MAX_HEAP_ACTOR
#define AKGL_MAX_HEAP_ACTOR                    64
#endif
#ifndef AKGL_MAX_HEAP_SPRITE
#define AKGL_MAX_HEAP_SPRITE                   (AKGL_MAX_HEAP_ACTOR * 16)
#endif
#ifndef AKGL_MAX_HEAP_SPRITESHEET
#define AKGL_MAX_HEAP_SPRITESHEET              AKGL_MAX_HEAP_SPRITE
#endif
#ifndef AKGL_MAX_HEAP_CHARACTER
#define AKGL_MAX_HEAP_CHARACTER                256
#endif
#ifndef AKGL_MAX_HEAP_STRING
#define AKGL_MAX_HEAP_STRING                   256
#endif

/** @brief The actor pool. Public so the render and physics sweeps can walk it directly instead of going through the registry. */
extern akgl_Actor akgl_heap_actors[AKGL_MAX_HEAP_ACTOR];
/** @brief The sprite pool. 16 per actor, on the assumption of one sprite per state combination. */
extern akgl_Sprite akgl_heap_sprites[AKGL_MAX_HEAP_SPRITE];
/** @brief The spritesheet pool. Sized like the sprite pool, though sharing means far fewer are used in practice. */
extern akgl_SpriteSheet akgl_heap_spritesheets[AKGL_MAX_HEAP_SPRITESHEET];
/** @brief The character pool. */
extern akgl_Character akgl_heap_characters[AKGL_MAX_HEAP_CHARACTER];
/** @brief The string pool. Every entry is PATH_MAX bytes, so this is the largest of the five by a wide margin. */
extern akgl_String akgl_heap_strings[AKGL_MAX_HEAP_STRING];

/**
 * @brief Zero every pool, marking every slot free.
 *
 * Call once at startup, before anything allocates. Calling it again is a reset,
 * not a refresh: it does not release textures, clear registries, or consult
 * reference counts, so every live object becomes a dangling pointer and every
 * registry entry points at a zeroed slot. akgl_game_init calls it for you.
 *
 * @return `NULL`. There is no failure path today -- it is a series of `memset`s
 *         -- but check it anyway; the signature exists so a layer that needs
 *         real setup has somewhere to report from.
 */
akerr_ErrorContext AKERR_NOIGNORE *akgl_heap_init(void);
/**
 * @brief Zero the actor pool only.
 *
 * Split out from akgl_heap_init so a caller can reset the actors between levels
 * while keeping the loaded sprites, sheets, and characters -- those are the
 * expensive ones, since they own textures. Pair it with
 * akgl_registry_init_actor, which clears the matching registry.
 *
 * @return `NULL`. No failure path today; see akgl_heap_init.
 */
akerr_ErrorContext AKERR_NOIGNORE *akgl_heap_init_actor(void);
/**
 * @brief Claim a free actor slot.
 * @param dest Receives a pointer to the free slot. Required, and **not**
 *             checked -- a `NULL` here is a crash, not an error context. The
 *             slot is *not* zeroed and its `refcount` is not incremented; it
 *             stays free until akgl_actor_initialize takes the reference.
 * @return `NULL` on success, otherwise an error context owned by the caller.
 * @throws AKGL_ERR_HEAP If every one of the #AKGL_MAX_HEAP_ACTOR slots is in use.
 */
akerr_ErrorContext AKERR_NOIGNORE *akgl_heap_next_actor(akgl_Actor **dest);
/**
 * @brief Claim a free sprite slot.
 * @param dest Receives a pointer to the free slot. Required and unchecked; not
 *             zeroed, and no reference taken. See akgl_heap_next_actor.
 * @return `NULL` on success, otherwise an error context owned by the caller.
 * @throws AKGL_ERR_HEAP If every one of the #AKGL_MAX_HEAP_SPRITE slots is in use.
 */
akerr_ErrorContext AKERR_NOIGNORE *akgl_heap_next_sprite(akgl_Sprite **dest);
/**
 * @brief Claim a free spritesheet slot.
 * @param dest Receives a pointer to the free slot. Required and unchecked; not
 *             zeroed, and no reference taken. See akgl_heap_next_actor.
 * @return `NULL` on success, otherwise an error context owned by the caller.
 * @throws AKGL_ERR_HEAP If every one of the #AKGL_MAX_HEAP_SPRITESHEET slots is
 *         in use.
 */
akerr_ErrorContext AKERR_NOIGNORE *akgl_heap_next_spritesheet(akgl_SpriteSheet **dest);
/**
 * @brief Claim a free character slot.
 * @param dest Receives a pointer to the free slot. Required and unchecked; not
 *             zeroed, and no reference taken. See akgl_heap_next_actor.
 * @return `NULL` on success, otherwise an error context owned by the caller.
 * @throws AKGL_ERR_HEAP If every one of the #AKGL_MAX_HEAP_CHARACTER slots is in
 *         use.
 */
akerr_ErrorContext AKERR_NOIGNORE *akgl_heap_next_character(akgl_Character **dest);
/**
 * @brief Claim a free string slot, and take the reference on it.
 *
 * The odd one out: this *does* increment `refcount`, so the slot is yours the
 * moment it returns and stays yours until you call akgl_heap_release_string.
 * That is what makes the scratch-buffer idiom -- claim, use, release in
 * `CLEANUP` -- safe. The contents are whatever the last holder left; call
 * akgl_string_initialize if you need it clean.
 *
 * @param dest Receives a pointer to the claimed slot. Required and **not**
 *             checked -- a `NULL` here is a crash, not an error context.
 * @return `NULL` on success, otherwise an error context owned by the caller.
 * @throws AKGL_ERR_HEAP If every one of the #AKGL_MAX_HEAP_STRING slots is in
 *         use. In practice this means a missing release somewhere, not a pool
 *         that is genuinely too small.
 */
akerr_ErrorContext AKERR_NOIGNORE *akgl_heap_next_string(akgl_String **dest);

/**
 * @brief Drop a reference to an actor, tearing it down when the last one goes.
 *
 * At zero it releases every child recursively, clears the actor's entry from
 * #AKGL_REGISTRY_ACTOR, and zeroes the slot.
 *
 * @param ptr The actor to release. Required. A slot whose `refcount` is already
 *            0 is re-torn-down rather than rejected, which is harmless on a
 *            zeroed slot and destructive on a live one that was never
 *            registered.
 * @return `NULL` on success, otherwise an error context owned by the caller.
 * @throws AKERR_NULLPOINTER If @p ptr is `NULL`.
 *
 * @warning Children are released unconditionally, and the recursion has no cycle
 *          check: an actor reachable from its own child list recurses until the
 *          stack runs out.
 */
akerr_ErrorContext AKERR_NOIGNORE *akgl_heap_release_actor(akgl_Actor *ptr);
/**
 * @brief Drop a reference to a sprite, tearing it down when the last one goes.
 *
 * At zero it clears the sprite's entry from #AKGL_REGISTRY_SPRITE and zeroes the
 * slot. The spritesheet it pointed at is *not* released -- the sprite only
 * borrowed it.
 *
 * @param ptr The sprite to release. Required.
 * @return `NULL` on success, otherwise an error context owned by the caller.
 * @throws AKERR_NULLPOINTER If @p ptr is `NULL`.
 */
akerr_ErrorContext AKERR_NOIGNORE *akgl_heap_release_sprite(akgl_Sprite *ptr);
/**
 * @brief Drop a reference to a spritesheet, destroying its texture when the last one goes.
 *
 * The only release that frees a resource outside the pool: at zero it clears the
 * entry from #AKGL_REGISTRY_SPRITESHEET, destroys the `SDL_Texture`, and zeroes
 * the slot. Any sprite still pointing at the sheet is left with a dangling
 * pointer, since nothing takes a reference on a sheet on a sprite's behalf.
 *
 * @param ptr The spritesheet to release. Required.
 * @return `NULL` on success, otherwise an error context owned by the caller.
 * @throws AKERR_NULLPOINTER If @p ptr is `NULL`.
 *
 * @note Destroying a texture is a main-thread operation in SDL, so this must be
 *       called from the thread that owns the renderer.
 */
akerr_ErrorContext AKERR_NOIGNORE *akgl_heap_release_spritesheet(akgl_SpriteSheet *ptr);
/**
 * @brief Drop a reference to a character, tearing it down when the last one goes.
 *
 * At zero it clears the entry from #AKGL_REGISTRY_CHARACTER and zeroes the slot.
 *
 * @param ptr The character to release. Required.
 * @return `NULL` on success, otherwise an error context owned by the caller.
 * @throws AKERR_NULLPOINTER If @p ptr is `NULL`.
 *
 * @note At zero it also walks the state-to-sprite map with
 *       akgl_character_state_sprites_iterate and #AKGL_ITERATOR_OP_RELEASE,
 *       giving back every reference akgl_character_sprite_add took, and then
 *       destroys the `SDL_PropertiesID` holding the map. Before 0.5.0 it did
 *       neither, so loading and releasing characters level by level exhausted
 *       the sprite pool and leaked a property set per character.
 */
akerr_ErrorContext AKERR_NOIGNORE *akgl_heap_release_character(akgl_Character *ptr);
/**
 * @brief Drop a reference to a pooled string, zeroing it when the last one goes.
 *
 * Strings are not registered anywhere, so this is just the reference count and a
 * wipe. It is safe to call on a string a function may or may not have claimed,
 * which is why the `CLEANUP` blocks in this library call it unconditionally.
 *
 * @param ptr The string to release. Required -- unlike the pattern elsewhere, a
 *            `NULL` here is an error rather than a no-op, so `CLEANUP` blocks
 *            wrap it in `IGNORE()`.
 * @return `NULL` on success, otherwise an error context owned by the caller.
 * @throws AKERR_NULLPOINTER If @p ptr is `NULL`.
 */
akerr_ErrorContext AKERR_NOIGNORE *akgl_heap_release_string(akgl_String *ptr);

#endif //_AKGL_HEAP_H_