[RohanFredriksson]

Picks the engine up from where the force-generator refactor left it in August 2024. This fixes the memory bugs that refactor introduced and makes the physics hold up for normal game scenes. It also adds tests and CI, finishes the half-built features, and adds a demo sandbox.

Memory-safety fixes

• Crash on reset or close: resetting or closing any scene with a Gravity component caused a heap-use-after-free, because World deleted force generator components that their entities also deleted. Entities now own them; the world only registers them.
• Killed bodies left in the grid: a killed rigidbody stayed in the physics spatial hash grid, so later steps used freed memory. Both crashes were reproduced under ASan before the fix.
• Window lifecycle: scene teardown order is fixed, and the window now deletes the scene, shaders, picking framebuffer and ImGui context on shutdown. The engine can also be started again after stop().

Physics

• Box/box collision: now a separating-axis test with reference face clipping. The old corner-in-box test missed edge overlaps, so identical boxes stacked on each other fell through.
• Circle/box collision: handles a circle whose centre has entered the box.
• Solver: replaced with warm-started sequential impulses. The step order is now velocities → solve → positions; integrating positions before solving made stacks collapse. A 5-row pyramid now stays standing at any frame rate.
• Mass properties: angular velocity integrates with the moment of inertia where it used mass, and the parallel-axis term uses each collider's own mass where it used the total.
• Bounds: bounds no longer always include the entity origin.
• Step limits: fixed steps are capped at 5 per frame.
• World gravity: the gravity argument was ignored and is now applied, with a per-body gravityScale.
• Raycasts: box raycasts are rewritten (the old version ignored the ray), circles behind the ray no longer hit, and World::raycast(ray, maxDistance) walks the grid.
• Debug drawing: off by default. It also used to allocate about 4.8 GB of GPU memory, which is fixed.

Engine and tools

• Spatial queries: the scene's unused entity spatial grid is now kept up to date and backs getEntitiesIn/Near/At.
• Scene files: they store gravity and the scene name, load audio from audio (it read fonts), and keep rigidbody velocity on load.
• Console: argument parsing and commands (help, save, load, reset, debug, gravity, entities, inspector), plus Console::registerCommand and Console::execute.
• Inspector: a new window where you click an entity to edit its components. Rigidbody has a panel now.
• Window size and high-DPI: Pancake::size sets the correct size, and the viewport follows the framebuffer size on high-DPI displays.
• Input: begin-down key and mouse queries last for the whole frame instead of being consumed by the first reader.
• Per-frame stall: removed a per-frame glReadPixels call.

Build, tests and CI

• CMake:
  • C++17 is now required explicitly.
  • AddressSanitizer is opt-in through PANCAKE_ASAN; it was always linked into games on Linux.
  • PANCAKE_BUILD_TESTS and PANCAKE_BUILD_EXAMPLES default to on only when Pancake is the top-level project.
• Tests:
  • Unit tests that need no window: spatial grid, collision, solver (resting, stacking, pyramid, angled drop, ball rest), force generators, raycasts and JSON round trips.
  • An engine test that runs the real loop and covers settle, save, reload, killing a body, resetting with force generators, and console commands.
  • A smoke run of the demo.
• CI: a GitHub Actions workflow builds with ASan and in Release, then runs everything under Xvfb.
• Demo: examples/demo.cpp is a physics sandbox.

Behaviour changes for existing games

These are also listed under "Upgrading" in the README.

• Gravity: world gravity now defaults to (0, -10). A game that added a Gravity component to get global gravity should remove it or set the world gravity to zero.
• Solver feel: restitution and friction may feel slightly different with the new solver. Bounces slower than 1 unit/s are ignored.
• Input: isKeyBeginDown and isMouseBeginDown now stay true for the whole frame.

Testing

• All 6 tests pass in both ASan and Release builds locally, including from a fresh clone of this branch.
• The demo was checked visually under Xvfb, with screenshots of the pyramid, debug drawing, console and inspector.
• Leak checking runs for the unit tests but is off for the tests that open a window, because the Mesa driver leaks memory from libraries it unloads, which can't be suppressed by name.

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https://claude.ai/code/session_01CSbmWwU5zh3ujWmjioWg1a

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