Expose JPH::PhysicsSystem::SetGravity / GetGravity#23
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Wraps the existing JPH::PhysicsSystem::SetGravity(Vec3Arg) and GetGravity() methods 1:1, mirroring the to_jph / to_jpc helper pattern used throughout JoltC.cpp. Vec3 conversion uses the existing helpers in JoltC.cpp lines 162-167. Motivation: the Jolt physics system's gravity is read by the integrator every step (it's not a per-body property — bodies have a GravityFactor multiplier on top). Until now there was no way to set or read system gravity from C-binding consumers, forcing them to either accept the hard-coded default (0, -9.81, 0) or apply gravity manually as per-body forces. Added in two places: - JoltC/Functions.h: declarations next to AddConstraint/RemoveConstraint - JoltCImpl/JoltC.cpp: implementations following the same `to_jph(self) -> JPH::PhysicsSystem*` -> method-call pattern as the existing PhysicsSystem wrappers PR submitted from Solidor777/JoltC:custom-gravity for upstream review. The Titan engine carries this patch locally on its mirror fork until upstream merges; once merged we sync from upstream and the local diff dissolves.
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Upstream PR for the JPC_PhysicsSystem_SetGravity export now has a URL: SecondHalfGames/JoltC#23. Cross-referenced from docs/VENDORING.md "Local patches" and docs/TODO.md so future syncs find the trigger. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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Upstream PR for the joltc-sys/build.rs Android cross-compile + host-vs-target /EHsc fix now has a URL: SecondHalfGames/jolt-rust#12. Cross-referenced from docs/VENDORING.md "Local patches" and docs/TODO.md so future syncs find the trigger. Pairs with SecondHalfGames/JoltC#23 (the SetGravity export PR opened earlier today). Both are independent; either can merge first. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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…atch Bumps the Solidor777/JoltC submodule to 547ad86, which mirrors JPH's per-arch JPH_VECTOR_ALIGNMENT logic on the C-side typedefs in JoltC/Functions.h (32-bit ARM falls back to 8/8 instead of 16/32). Without the patch, every JPC_*Settings struct that contains a vector field (ShapeCast, CollideShape, BodyManager_Draw, ContactPoints, ContactManifold, …) failed the LAYOUT_COMPATIBLE static_assert in JoltC.cpp on armv7-linux-androideabi with `align of JPC_<X> did not match align of JPH::<X> (16 == 8)`. Verified locally: armv7 + aarch64 cargo-ndk cross-compile both succeed. CI matrix: armv7-linux-androideabi flips to include_jolt: true; the mobile-build-test job loses continue-on-error: true (now a hard PR gate — every entry passes reliably). iOS validation with Jolt still pending (no Apple hardware on the dev machine). VENDORING.md: drops the SetGravity TITAN PATCH entry (PR SecondHalfGames/JoltC#23 was merged + LPGhatguy's follow-up cleanup synced into our fork). Adds the JPC_VECTOR_ALIGNMENT entry; upstream PR URL appended once filed. POST_WORK_FINDINGS / TODO / PLAN updated to reflect the resolved state. 4 gates green (507 tests). Editor smoke-launch reached `titan-host: boot complete` with no panics. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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## Summary
Two coupled bugs surfaced while cross-compiling `joltc-sys` to Android
(aarch64-linux-android via NDK r26d clang from a Windows host).
### 1. `cfg!(windows)` is a HOST-OS check, not a target-OS check
`build.rs` runs on the host. When the host is Windows and the target is
Android, the existing `if cfg!(windows) { config.cxxflag("/EHsc"); }`
unconditionally appends the MSVC-only `/EHsc` flag. NDK clang then
receives `/EHsc` as a path argument and errors with `no such file or
directory: '/EHsc'`.
**Fix:** read `CARGO_CFG_TARGET_OS` and gate `/EHsc` on the actual
target.
### 2. Native Android cross-compile setup is missing
Building for Android via the standard `cargo ndk --target
<android-triple> check -p joltc-sys` flow currently fails because
`joltc-sys` does not set:
- `CMAKE_TOOLCHAIN_FILE` (NDK's `build/cmake/android.toolchain.cmake`).
- `ANDROID_ABI` (the toolchain reads it as a CMake `-D` variable; env
var is ignored).
- The CMake generator (cmake-rs defaults to MSBuild on Windows hosts;
the NDK toolchain only supports Ninja / Makefiles).
**Fix:** when `target_os == "android"`, derive `ANDROID_ABI` from
`CARGO_CFG_TARGET_ARCH` (`aarch64` → `arm64-v8a`, `arm` → `armeabi-v7a`,
`x86` / `x86_64` 1:1), resolve the NDK from `ANDROID_NDK_HOME` /
`ANDROID_NDK_ROOT` / `ANDROID_NDK`, force `Ninja`, and pin
`ANDROID_PLATFORM=android-21`.
## End-user contract after this change
```sh
export ANDROID_NDK_HOME=/path/to/ndk # or ANDROID_NDK_ROOT / ANDROID_NDK
cargo ndk --target aarch64-linux-android check -p joltc-sys
```
The standard cargo-ndk + `nttld/setup-ndk@v1` GitHub Action workflow
Just Works.
## Validation
- Locally validated on Windows host → aarch64-linux-android with NDK
r26d. Full `JoltPhysics + JoltC + joltc-sys + rolt` cross-compile
completes in ~20s. Downstream Rust crate (Titan engine's
`titan-jolt-3d`) builds against the cross-compiled libs.
- `armv7-linux-androideabi` is **not addressed by this PR** — it hits an
unrelated `JoltC` `LAYOUT_COMPATIBLE` static_assert (`JPC_*Settings`
16-byte alignment vs `JPH::*Settings` 8-byte alignment on 32-bit ARM).
That looks like a JoltC-side ABI bug for 32-bit targets; happy to track
separately.
- Desktop targets (Win/Linux/macOS) are unaffected — Android branch is
gated on `target_os == "android"`, and the `/EHsc` change only narrows
the existing condition (Windows targets still get it).
## Test plan
- [x] `cargo check -p joltc-sys` on Windows host (default target,
x86_64-pc-windows-msvc) — `/EHsc` still applied; existing behavior
unchanged.
- [x] `cargo ndk --target aarch64-linux-android check -p joltc-sys` on
Windows host — succeeds with only `ANDROID_NDK_HOME` set.
- [ ] `cargo ndk --target aarch64-linux-android check -p joltc-sys` on
Linux + macOS hosts — reviewer to validate; should be the simpler case
(no `/EHsc` hot path).
- [ ] `cargo check -p joltc-sys` on Linux/macOS — unaffected; existing
CI covers.
Opened from the same Titan-engine fork that submitted
SecondHalfGames/JoltC#23 (the `JPC_PhysicsSystem_SetGravity` export).
Both PRs are independent — happy to address review feedback on either.
---------
Co-authored-by: Lucien Greathouse <me@lpghatguy.com>
Solidor777
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May 13, 2026
…s#23 (gravity) # Conflicts: # JoltC/Functions.h
Solidor777
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May 17, 2026
Upstream PR for the JPC_PhysicsSystem_SetGravity export now has a URL: SecondHalfGames/JoltC#23. Cross-referenced from docs/VENDORING.md "Local patches" and docs/TODO.md so future syncs find the trigger. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Solidor777
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May 17, 2026
Upstream PR for the joltc-sys/build.rs Android cross-compile + host-vs-target /EHsc fix now has a URL: SecondHalfGames/jolt-rust#12. Cross-referenced from docs/VENDORING.md "Local patches" and docs/TODO.md so future syncs find the trigger. Pairs with SecondHalfGames/JoltC#23 (the SetGravity export PR opened earlier today). Both are independent; either can merge first. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Solidor777
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May 17, 2026
…atch Bumps the Solidor777/JoltC submodule to 547ad86, which mirrors JPH's per-arch JPH_VECTOR_ALIGNMENT logic on the C-side typedefs in JoltC/Functions.h (32-bit ARM falls back to 8/8 instead of 16/32). Without the patch, every JPC_*Settings struct that contains a vector field (ShapeCast, CollideShape, BodyManager_Draw, ContactPoints, ContactManifold, …) failed the LAYOUT_COMPATIBLE static_assert in JoltC.cpp on armv7-linux-androideabi with `align of JPC_<X> did not match align of JPH::<X> (16 == 8)`. Verified locally: armv7 + aarch64 cargo-ndk cross-compile both succeed. CI matrix: armv7-linux-androideabi flips to include_jolt: true; the mobile-build-test job loses continue-on-error: true (now a hard PR gate — every entry passes reliably). iOS validation with Jolt still pending (no Apple hardware on the dev machine). VENDORING.md: drops the SetGravity TITAN PATCH entry (PR SecondHalfGames/JoltC#23 was merged + LPGhatguy's follow-up cleanup synced into our fork). Adds the JPC_VECTOR_ALIGNMENT entry; upstream PR URL appended once filed. POST_WORK_FINDINGS / TODO / PLAN updated to reflect the resolved state. 4 gates green (507 tests). Editor smoke-launch reached `titan-host: boot complete` with no panics. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Solidor777
added a commit
to Solidor777/Titan
that referenced
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Jun 4, 2026
Upstream PR for the JPC_PhysicsSystem_SetGravity export now has a URL: SecondHalfGames/JoltC#23. Cross-referenced from docs/VENDORING.md "Local patches" and docs/TODO.md so future syncs find the trigger. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Solidor777
added a commit
to Solidor777/Titan
that referenced
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Jun 4, 2026
Upstream PR for the joltc-sys/build.rs Android cross-compile + host-vs-target /EHsc fix now has a URL: SecondHalfGames/jolt-rust#12. Cross-referenced from docs/VENDORING.md "Local patches" and docs/TODO.md so future syncs find the trigger. Pairs with SecondHalfGames/JoltC#23 (the SetGravity export PR opened earlier today). Both are independent; either can merge first. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Solidor777
added a commit
to Solidor777/Titan
that referenced
this pull request
Jun 4, 2026
…atch Bumps the Solidor777/JoltC submodule to 547ad86, which mirrors JPH's per-arch JPH_VECTOR_ALIGNMENT logic on the C-side typedefs in JoltC/Functions.h (32-bit ARM falls back to 8/8 instead of 16/32). Without the patch, every JPC_*Settings struct that contains a vector field (ShapeCast, CollideShape, BodyManager_Draw, ContactPoints, ContactManifold, …) failed the LAYOUT_COMPATIBLE static_assert in JoltC.cpp on armv7-linux-androideabi with `align of JPC_<X> did not match align of JPH::<X> (16 == 8)`. Verified locally: armv7 + aarch64 cargo-ndk cross-compile both succeed. CI matrix: armv7-linux-androideabi flips to include_jolt: true; the mobile-build-test job loses continue-on-error: true (now a hard PR gate — every entry passes reliably). iOS validation with Jolt still pending (no Apple hardware on the dev machine). VENDORING.md: drops the SetGravity TITAN PATCH entry (PR SecondHalfGames/JoltC#23 was merged + LPGhatguy's follow-up cleanup synced into our fork). Adds the JPC_VECTOR_ALIGNMENT entry; upstream PR URL appended once filed. POST_WORK_FINDINGS / TODO / PLAN updated to reflect the resolved state. 4 gates green (507 tests). Editor smoke-launch reached `titan-host: boot complete` with no panics. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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Summary
Adds C wrappers for
JPH::PhysicsSystem::SetGravity(Vec3Arg)andGetGravity(), exposing per-system gravity control to JoltC consumers (joltc-sys, rolt, downstream Rust bindings, LuaJIT bindings, etc.).Motivation
Jolt's
PhysicsSystemstores gravity internally and the integrator reads it every step. Without a C wrapper, consumers are locked to Jolt's default(0, -9.81, 0)and cannot implement gameplay features like low-gravity power-ups, alien-planet biomes, or per-region gravity overrides. Per-bodyGravityFactoris a scalar multiplier and cannot redirect gravity, so it does not substitute.Implementation
JoltC/JoltC/Functions.h— declarations placed next toAddConstraint/RemoveConstraint(line ~1626).JoltC/JoltCImpl/JoltC.cpp— implementations using the existingto_jph(self) -> JPH::PhysicsSystem*+to_jph(JPC_Vec3)/to_jpc(JPH::Vec3)helper pattern (lines 162-167 ofJoltC.cpp).17 lines total. No allocations, no behavioral changes to existing APIs — purely additive.
Test plan
titan-jolt-3dcrate, which vendors joltc-sys + rolt) callsJPC_PhysicsSystem_SetGravityper step; bodies accelerate along the supplied gravity vector. New unit test verifies+Xgravity moves a body along+X.Opened from a downstream-vendoring fork; happy to address review feedback or split the change if preferred.