psxrecomp/docs/MOD_PACKAGES.md

PSXRecomp mod packages and features

A .psxmod is a versioned installation, provenance, and trust boundary. A package may contribute any number of independently configurable features. The launcher presents those features as the primary Mods list; package installation, version selection, and removal are a secondary management view.

Feature identity is always (package_id, feature_id). Enabling one feature never enables, disables, or reconfigures another feature.

The player selects a verified stock BIN/CUE. Resolution produces guarded native operations and sparse disc overlays without rewriting or replacing that stock image.

Where packages live

Two catalog roots sit beside the executable, split by who owns the files:

<exe>/mods/
  bundled/     build output — the framework's mods/builtin/packages plus the
               title's mods/preloaded/packages. Every build WIPES and re-stages
               this tree, so nothing a player owns may live here.
  installed/   launcher-owned — .psxmod archives installed through the Mods
               manager. No build ever touches this tree.
  state.toml   user selection state (enabled features, option values).

Both roots use the same <package-id>/<version>/manifest.toml layout and are scanned into one catalog, bundled first. An installed package with the same id as a bundled one deliberately shadows it and records that it did so, so an override is visible rather than decided by directory-iteration order.

A bundled package is not removable from the Mods page: deleting build output would succeed and then be undone by the next build. Remove it from the title's mods/preloaded/packages instead.

Only bundled/ ships in a release. installed/ and state.toml are the local machine's and are excluded by every packager.

Migration. A pre-split install has one mods/packages/ tree holding both. The first scan moves each package the current build did not also stage into installed/, drops the rest as redundant build output, and removes the old tree — but only once every version directory has been dealt with. Anything that could not be moved is left exactly where it is and reported.

A manifest that fails to parse is never skipped silently: it is reported by scan_errors() and logged, naming the path and the reason.

Feature manifest

Write new manifests at the current format version, which is 6. Older versions stay readable so installed packages survive an update, and each section below notes the version a field first required.

format_version = 6
id = "example.localization"
version = "1.2.0"
name = "Example Localization Pack"
author = "Example Author"
description = "Independent title and script features."
license = "MIT"
resolver = "declarative"

[[target]]
game_id = "SLUS-00000"
# Required for disc overlays. Use the digest of the supported stock image.
disc_sha256 = "0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef"

[[feature]]
id = "title-screen"
name = "Title Screen"
description = "Selects the title-screen artwork."
group = "Localization"
default_enabled = false

[[feature]]
id = "retranslation"
name = "Retranslation"
description = "Uses the revised English script."
group = "Localization"

[[option]]
feature = "title-screen"
id = "variant"
label = "Title artwork"
type = "choice"
default = "rockman"

[[option.choice]]
value = "mega-man"
label = "Mega Man X6 (USA)"

[[option.choice]]
value = "rockman"
label = "Rockman X6 (Japan)"

[[patch]]
feature = "title-screen"
target = "main_exe"
address = 0x80041234
expected = "2a 00 02 24"
replace = "0e 00 02 24"
when = { variant = "rockman" }

[[overlay]]
feature = "retranslation"
target = "disc_raw"
offset = 123456
file = "assets/retranslated-script.bin"
sha256 = "..."
# Optional additional guard over the same range in the stock image.
expected_sha256 = "..."

Every [[option]], [[patch]], and [[overlay]] in a feature-style manifest must name its owning feature. Ambiguous operations are rejected.

Option types are boolean, choice, and bounded integer. Conditions are feature-local: when = { option = "value", ... } requires every listed option to match. The legacy when_option/when_value pair remains accepted for a single condition.

Bounded integer patches

Package format 2 can encode a bounded integer option directly into a guarded write:

format_version = 2

[[feature]]
id = "starting-lives"
name = "Starting Lives"

[[option]]
feature = "starting-lives"
id = "count"
label = "Lives"
type = "integer"
min = 0
max = 99
step = 1
default = 2

[[patch]]
feature = "starting-lives"
target = "main_exe"
address = 0x8001DE64
expected = "02 00 02 24"
replace_from = { option = "count", encoding = "u16le", offset = 0 }

[[patch]]
feature = "starting-lives"
target = "main_exe"
address = 0x8001DE70
expected = "03 00 02 24"
replace_from = { option = "count", encoding = "u16le", offset = 0, addend = 1 }

replace_from and literal replace are mutually exclusive. The referenced option must be a bounded integer owned by the same feature. The initial encodings are u8, u16le, and u32le. offset selects a byte field inside the expected guard and defaults to zero. Generated replacement bytes begin as an exact copy of the expected bytes, then the encoded value replaces only that field. This lets a MIPS immediate, for example, retain a guard and collision claim over its complete instruction. addend is the only supported transform, and the complete declared option range after that addend must fit the unsigned encoding.

There is deliberately no host-endian encoding, signed inference, mask, shift, scale, expression language, or partial-field merge. A package uses multiple guarded [[patch]] entries when the same value has multiple destinations. Generated bytes enter the ordinary pre-boot write plan, collision checks, and fingerprint. A generated value identical to the stock guard is omitted as a no-op, so an enabled stock-valued option does not claim or conflict on bytes it does not change.

Integer values use canonical decimal text. Leading plus signs, redundant leading zeroes, values outside the bounds, and values not aligned to step are rejected.

Ordered values and split MIPS immediates

Package format 3 adds feature-local ordering constraints for related integer fields:

format_version = 3

[[constraint]]
feature = "rank-thresholds"
kind = "ordered_integer"
direction = "nondecreasing"
options = ["rank-c", "rank-b", "rank-a"]

All listed options must be integer options on that feature. Defaults must satisfy the constraint. While a feature is enabled, an edit that would invert the order is rejected with the neighboring option labels. Disabled features may retain an incomplete or invalid draft, but cannot be enabled until it is valid. nonincreasing is also supported.

Format 3 also provides a narrow, typed transform for constants constructed by a linked MIPS LUI/ORI pair:

replace_from = {
  option = "speed",
  encoding = "mips_lui_ori_u32",
  omit_when_default = true
}

The patch must target one aligned, fully guarded eight-byte main_exe instruction pair. The loader verifies the opcodes and register linkage, then places the raw high and low 16-bit halves into the two immediates. It does not apply signed-ADDIU carry adjustment. offset and addend are not accepted for this encoding.

omit_when_default suppresses the entire patch when the selected value equals the option default. This models source tools whose declared default means "make no writes," including cases where multiple guarded sites contain different stock values. For any nondefault selection, every declared site retains its collision claim even if one generated replacement happens to equal its stock guard.

Sparse fields and integer predicates

Package format 4 separates a patch's complete expected-byte guard from the fields it owns and writes. This is for semantic records whose independently configurable fields share one useful guard:

format_version = 4

[[option]]
feature = "saber-timing"
id = "frames"
label = "Frames"
type = "integer"
min = 0
max = 99
default = 2

# Positive values change only byte 0.
[[patch]]
feature = "saber-timing"
target = "main_exe"
address = 0x80077640
expected = "02 42 01 02"
fields = [
  { offset = 0, option = "frames", encoding = "u8" },
]
when_integer = { option = "frames", op = "gt", value = 0 }

# Zero has a narrow, explicitly declared compound representation.
[[patch]]
feature = "saber-timing"
target = "main_exe"
address = 0x80077640
expected = "02 42 01 02"
fields = [
  { offset = 0, replace = "01" },
  { offset = 2, replace = "00" },
]
when_integer = { option = "frames", op = "eq", value = 0 }

fields is mutually exclusive with replace and replace_from. Every field has a nonnegative offset and exactly one payload form:

• replace = "..." supplies non-empty literal bytes; or
• option plus encoding uses a bounded integer option on the same feature, with the optional checked addend.

Fields must fit inside expected and their owned byte ranges may not overlap. The supported dynamic encodings are the existing u8, u16le, u32le, and linked mips_lui_ori_u32 forms. A sparse MIPS field owns only the two immediate halfwords while the complete linked instruction pair remains guarded; as with format 3, that encoding does not accept an addend.

Resolution omits individual fields whose generated payload already equals the guard. If no field changes, the patch is a no-op. Otherwise the plan retains the complete guard and the exact remaining owned ranges. Runtime guard validation checks every byte of expected before applying any writes, while collision detection and writing use only the owned fields. Thus two features can safely own adjacent bytes in one record without either overwriting the other. Overlapping guards must still agree on their expected bytes; conflicting guards make the plan unsatisfiable and are rejected.

when_integer is a patch-level, feature-local predicate over one bounded integer option. op is exactly one of eq, ne, lt, le, gt, or ge, and value is an integer constant inside the option bounds. Equality constants must also be selectable under the option's step. String-valued when conditions and one when_integer predicate may coexist and are ANDed.

Sparse fields and integer predicates are still pre-boot plan construction. They do not provide a general expression evaluator, masks, arithmetic beyond the checked field addend, package code execution, or per-frame dispatch.

Channels

A feature declares how finished it is. Format 6 puts channel on the feature, not the package:

format_version = 6
id = "example.enhancements"

[[feature]]
id = "widescreen"
channel = "experimental"     # ships, badged, default off

[[feature]]
id = "hook-trace"
channel = "developer"        # absent from any release build

Channel	Ships	In the launcher
stable (default)	yes	no tag — the absence is the stable case
experimental	yes	amber EXP tag, and a line saying it is unvalidated
developer	no	secondary-accent DEV tag; only ever visible on a local build

An absent channel means stable. A package may still declare one, which its features inherit unless they state their own — which is how a format-5 manifest carrying a package-level channel keeps working unchanged.

Why the feature and not the package. A package is the installation and trust boundary; how finished one of its features is has nothing to do with that. When the marker sat on the package, a catalog holding one player-ready feature and one developer instrument had to declare itself entirely developer — so neither shipped, and the documented workaround was to split the catalog into two packages. Channels per feature remove that trade.

"Developer does not ship" means absent, not hidden. Two mechanisms, one per catalog root:

• bundled/ is filtered when it is staged. tools/mod_channel_filter.py emits a manifest without the developer features and without the [[option]], [[patch]], [[overlay]], [[plugin]], [[resource]] and [[constraint]] entries that only served them; a package whose every feature is developer has its directory removed. This is generation, not rewriting: the staged catalog is build output and the author's manifest in the repo is never touched.
• installed/ is refused at load. A third-party archive is never modified, so the runtime declines to surface developer features from one instead.

The runtime gate is the build definition PSX_MOD_DEVELOPER_CHANNEL, which runtime.cmake sets for a local build and clears under $CI. A contributor reaches developer features by cloning the repo and building; a release build carries neither the features nor their operations, so a stale state.toml naming one cannot reach them either.

Packaging defaults the exclusion from $CI — on under any CI provider, off locally. --exclude-dev-mods / --include-dev-mods (or EXCLUDE_DEV_MODS=0|1) override it, and project_studio build export --exclude-dev-mods reproduces what a release would contain.

Trusted static plugins

Package format 5 can activate a game-owned plugin that is already statically linked into the executable:

format_version = 5

[[feature]]
id = "warp-debug-menu"
name = "Warp Debug Menu"

[[plugin]]
feature = "warp-debug-menu"
id = "example.warp-debug"

The plugin id is a stable registry key, not a library path or symbol name. The package archive supplies no native code. Resolution fails before launch when an enabled plugin has no registered implementation or when two features claim the same plugin id. Active plugin identities and owners participate in the canonical plan fingerprint.

An implementation may register an activation callback, a deterministic guest-VBlank callback, or both under the same id. Activation runs after the launcher's final mod-plan commit and before renderer/window initialization; it is appropriate for a game-owned mod that selects a fixed display aspect or another pre-boot host feature. VBlank callbacks run from the emulated GPU VBlank event, independent of host presentation, pacing, turbo, or skipped frames. Trusted callbacks receive only the narrow C services exposed by runtime/include/mod_plugins.h. Games should continue to use declarative patches and overlays when those operations are sufficient.

psx_mod_set_load_acceleration(multiplier, release_frames) is the narrow pre-boot service for a game-owned fast-loading feature. It changes host wall-clock pacing only: guest VBlanks, CD deadlines, interrupts, callbacks, and game logic still execute. Multipliers 2 through 16 are bounded choices; zero selects uncapped host speed. A zero-frame release stops acceleration as soon as the sustained-load predicate clears, which is appropriate for timing-sensitive or speedrun-oriented packages.

psx_mod_set_disc_speed(divisor, instant_max_per_frame) is the guest-visible alternative. Divisors 2 and 4 shorten emulated CD deadlines; zero selects the bounded instant scheduler. Because this changes interrupt timing, packages should label it experimental and make it mutually exclusive with host-only load acceleration (normally as choices in one default-off feature).

Native operations

main_exe writes use PSX guest virtual addresses. Expected bytes are checked after the BIOS loads the executable, then the complete write plan is applied before its entry point. Changed executable ranges use the existing dirty-RAM interpreter/native-overlay machinery; untouched functions remain on the static native path.

Small disc_raw and disc_user patches are equal-length guarded writes and may not cross a sector boundary:

• disc_raw offsets use lba * 2352 + byte_in_sector.
• disc_user offsets use lba * 2048 + byte_in_sector.

File-backed [[overlay]] operations are intended for large assets and may span any number of sectors. Their paths must remain inside the archive. Payload size and SHA-256 are verified while scanning, but disabled payloads are not retained in memory. Enabled payloads are loaded and reverified during resolution, then indexed by target and LBA before boot. A CD read performs a direct indexed lookup rather than scanning every installed mod.

Feature disc overlays require an exact disc_sha256 on every target entry. expected_sha256 can additionally guard the replaced stock range.

State and migration

mods/state.toml format 2 stores selected package versions separately from per-feature enabled states and values:

format_version = 2

[[package]]
id = "example.localization"
version = "1.2.0"

[[feature]]
package_id = "example.localization"
id = "title-screen"
enabled = true

[feature.values]
variant = "rockman"

[feature.resources]
artwork = "C:/Users/You/Pictures/example-bezel.png"

State format 1 and package-only manifests remain readable as a migration aid. They appear through one synthetic legacy feature. New packages should use explicit features.

The old derived_disc VCDIFF mechanism is legacy conversion scaffolding only. Feature-style manifests reject it. It is not a product mod primitive, fallback, or image-selection workflow; patched discs may be used offline as parity oracles while converting known mods to native operations.

Resolution and diagnostics

Before boot, the manager:

1. verifies the selected stock game and revision;
2. expands only enabled features and their selected options;
3. orders active packages deterministically by dependencies;
4. verifies enabled payloads and operation bounds;
5. collision-checks the complete owned byte-range plan and guard compatibility;
6. coalesces only truly identical target/range/expected/replacement writes or identical overlays; and
7. produces a canonical SHA-256 plan fingerprint.

Incompatible overlaps fail before launch. Structured diagnostics identify both (package, feature) owners and the exact contested target range. The launcher marks both feature rows and lets the user decide what to disable. It never silently chooses a winner.

Operation boundaries are not semantic boundaries. Legacy full-record writes compose when both their expected and replacement bytes agree throughout the owned intersection. Format-4 sparse patches collide only on declared owned fields, while their complete guards must remain mutually compatible. Partially overlapping overlays compose when their replacement payload bytes agree. A differing owned byte or incompatible guard produces a diagnostic at that exact location. Exact duplicate operations may be coalesced.

Package-level dependencies and conflicts are reserved for actual implementation relationships. Mutually exclusive choices such as US versus Japanese artwork belong inside one feature as option values.

Trusted adapters and archive safety

Owner-selected resources

Format-5 packages may declare feature-owned resources that the launcher renders with its native file/folder picker:

[[resource]]
feature = "bezel"
id = "artwork"
label = "Bezel image"
description = "Select an image to draw behind the game frame."
format = "file"
file_patterns = "*.png,*.jpg,*.jpeg,*.bmp"
file_description = "Image files"
required = false

Resources are paths selected by the player and persisted in mods/state.toml; they are not copied into the package. Optional resources with no selected path are omitted from the committed plan. Required resources reject launch while the feature is enabled and unset.

resolver = "builtin:<id>" selects a resolver statically registered by the game. Format-5 plugin ids likewise select only statically registered implementations. Packages cannot load arbitrary native code or select arbitrary symbols.

The installer accepts stored or DEFLATE-compressed ZIP entries, validates CRCs, rejects encrypted entries and unsafe or absolute paths, limits archives to 4096 files and 256 MiB expanded size, stages extraction, validates the manifest, and publishes the version atomically.

Presentation bezel packages

The framework registers psx.bezel, a trusted presentation plugin for OpenGL margin artwork. The built-in package declares an optional artwork image resource; when the feature is enabled and the player has selected an image, the runtime draws that image behind the game frame before presenting the normal 4:3 or widescreen content.

The built-in package psx.presentation.bezel targets every game but defaults to off, so the default presentation is unchanged: letterbox and pillarbox margins remain black. Enabling the feature without choosing artwork is also a no-op. The package supplies only the declaration and trusted plugin selection; archives still cannot load native code.