OpenTTD on Mac OS 9 / PowerPC

An experimental port of OpenTTD to classic Mac OS 8/9 running on PowerPC, built with the Retro68 cross-compiler toolchain.

This repository is the working scratch space for that port: a progression of small, individually bootable PPC applications that each prove one more piece of the game running on 25-year-old hardware — from a "hello world" up to the real OpenTTD engine simulating a growing town and the canonical game UI drawing itself, all in a single PowerPC binary.

Status: experimental / research port. Everything described below has been confirmed on real Mac OS 9 PowerPC hardware (not just an emulator), unless noted otherwise. It is not a playable game yet — it's a milestone-driven journey toward one.

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What actually runs

The furthest-along build (ottd-r1) boots on Mac OS 9 / PPC and shows, all drawn by OpenTTD's own source (viewport.cpp / window.cpp / widget.cpp / strings.cpp / toolbar_gui.cpp):

• an organic value-noise world — hills, a lake, a river, forests, industries;
• five towns growing live, with real generated town names floating over them;
• a moving vehicle;
• the full canonical OpenTTD toolbar — real buttons, dropdown menus that open with real text;
• a draggable, closeable in-game window;
• a real player company, which lights up the build/finance/vehicle toolbar buttons.

Underneath, the real headless engine (ottd-m1) runs the genuine game loop: the calendar advances, a real Town lives in the real TownPool, OpenTTD's command dispatch executes real tile commands, and GrowTown() grows a town to 100+ houses with a real road network and population accounting.

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Screenshots

Real Mac OS 9 / PowerPC hardware — the ottd-r1 build running on the actual machine (captured over VNC).

A real, moving economy: OpenTTD's own CompanyFinancesWindow — company "Clamshell Transport", pound-sterling balance, categorized revenue/expenses (loan interest, upkeep), max loan — over the live world, with a stats HUD (population, company money, industry cargo stockpile, stations). Real pooled Company, Vehicle, Industry and Station objects drive it, no fakes:

The full world with five live, named towns, a lake and a river, forests and industries — all rendered by OpenTTD's own viewport.cpp on PPC:

The canonical OpenTTD toolbar plus a zoomed-in town (Peningley) — houses, roads, a stadium, and autumn trees:

A draggable in-game "Towns" window, drawn by the real window.cpp / widget.cpp stack (Year 1950 · 5 towns · population 3250):

Offline render-pipeline previews (host-side, used to debug geometry)

These are not hardware captures — they come from the Python render simulators in agent-compositor/ and agent-tiles/, which reproduce the port's isometric tile math on the host so landscape geometry and sprite selection could be debugged without burning hardware round-trips.

Composited landscape scene (agent-compositor/preview/scene.png):

Individual tile sprites the renderer selects and projects (agent-tiles/previews/):

Flat grass	Sloped grass	Water	Trees	Rocky

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Subprojects

Each directory is a self-contained CMake application built for PowerPC. Roughly chronological:

Directory	What it proves
hello-ppc, hello-console	Toolchain bring-up — first code running on PPC / Mac OS 9.
ottd-thread-demo	Cooperative threading model (std::thread shim over the Mac event loop).
ottd-date-demo	Real OpenTTD calendar/date math on PPC.
ottd-fileprobe	POSIX opendir/readdir/stat backed by the Mac File Manager.
ottd-gfx-demo	GRF sprite decode + the 8bpp blitter drawing real sprites.
ottd-landscape	Landscape / ground-sprite rendering.
ottd-gamelogic	Map + tile logic on the real data structures.
ottd-b1, ottd-b1min	B1 — first full one-shot landscape render (b1min = minimal bisection variant used to isolate linker crashes).
ottd-b2	B2 — a live VideoDriver_MacClassic: WaitNextEvent main loop, dirty-rect CopyBits, mouse pan/zoom/pick, plus the OS seams (sockets, dirents, cooperative sleep) and a permanent regression harness.
ottd-m1	M1 — the real OpenTTD engine running headless on PPC: date ticks, real Town pool, command dispatch, tile commands, roads, and a town that grows.
ottd-r1	R1 — the render merge: M1 engine + B2 video pipeline + the real OpenTTD window/UI stack + a real company, in one binary. The most complete build.
agent-compositor, agent-tiles	Offline Python tooling — render simulators (PIL) and tile-sprite generation used to debug geometry without burning hardware round-trips.
compat	The portability shims: dirent.h, mac_sockets.h, libc_compat.h, and cooperative thread / mutex / condition_variable.

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OS seams

Porting to classic Mac OS meant re-implementing the POSIX/runtime surface OpenTTD assumes, on top of Toolbox and Open Transport. Status:

• Video ✅ — VideoDriver_MacClassic (WaitNextEvent + dirty-rect CopyBits, palette animation).
• File system ✅ — opendir/readdir/stat via the File Manager (PBGetCatInfo).
• UDP sockets ✅ — BSD sendto/recvfrom over Open Transport.
• TCP sockets ✅ — non-blocking connect/send and listen/accept/recv over Open Transport (client + server, loopback-proven).
• Cooperative runtime ✅ — sleep_for yields the CPU back to Mac OS via the event pump; condition-variable pumping still partial.

A regression harness in ottd-b2 re-runs the socket seam tests on every launch and reports one greppable verdict line each.

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Building & deploying

Prerequisites: the Retro68 toolchain (built for powerpc-apple-macos) and its Open Transport SDK. The toolchain itself is not vendored here (see .gitignore).

Each subproject builds with CMake against the Retro68 toolchain file, e.g.:

cd ottd-m1
cmake -B build -DCMAKE_TOOLCHAIN_FILE=<retro68>/powerpc-apple-macos/cmake/retroppc.toolchain.cmake .
cmake --build build --target ottdm1_APPL

This produces a MacBinary (.bin) / PEF .APPL you copy to the Mac and decode. The larger builds (ottd-m1, ottd-r1) use a build.sh to hand-compile the real OpenTTD translation units into obj/ first, with the port's merge flags, before the CMake link step. Runtime logging goes out over the UDP socket seam to a network log sink.

The checked-in deployable binaries (*.APPL, *.pef, *.bin, *.ad) are the actual artifacts that ran on hardware. Regenerable intermediates (*.xcoff, *.o, …) are git-ignored.

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Toolchain notes (the hard-won part)

A sampling of the Retro68 / XCOFF-PPC landmines this port had to work around — the reusable gold:

• --gc-sections is a no-op in this binutils XCOFF linker. Every compiled translation unit links whole, so pulling in one real OpenTTD .cpp drags its entire undefined-symbol surface. Bounding each unit with header-matched no-op stubs is mandatory, not optional.
• Duplicate symbols crash ld (SIGSEGV) instead of erroring cleanly. "Silent linker crash" almost always means a multiple definition between a real TU and a stub — dedup with #ifndef guards.
• dynamic_cast on a real polymorphic object bus-errors — RTTI is broken on Retro68/XCOFF PPC. Replaced with static_cast where the type is known and hand-written virtual As*() downcast helpers where the parser needs null-on-mismatch.
• std::chrono::steady_clock is broken — swapped for a TickCount()-based clock.
• Bare assert() aborts silently on Mac (no message reaches the log). A valid-looking op that just stops is usually a tripped assert — build with -DNDEBUG for release paths.
• Zeroed "deadpool" globals silently disable real code paths. When a real flag won't fire, suspect an upstream _settings_*==0 guard sitting in zeroed storage.

The agent-* Python simulators exist precisely because hardware round-trips are expensive — reproducing render/geometry bugs offline (via the real coordinate math) pointed straight at fixes without repeated deploys.

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Licensing

This repository is licensed under the GNU General Public License, version 2 (see LICENSE).

It is a port of, and derivative work based on, OpenTTD — which is itself GPL v2. This project compiles OpenTTD translation units, adapts OpenTTD source into its shim/scene files, and links OpenTTD code into every deployable binary (*.APPL, *.pef, *.bin). Because the whole is a work based on the Program, GPL v2 governs the whole, and the port code is offered under the same terms. There is no proprietary or permissively-licensed carve-out.

Attribution for OpenTTD and the Retro68 toolchain is in NOTICE.

Credits

• OpenTTD — the open-source Transport Tycoon Deluxe reimplementation being ported (GPL v2).
• Retro68 — the GCC cross-compiler and runtime for classic 68k/PowerPC Mac OS that makes this possible.