Intro
We just finished a solid development sprint on AmiWriterMUI — a lightweight MUI text editor for AmigaOS 4.1. It’s built with the OS4 SDK and TextEditor.mcc, and it’s been rapidly iterated with Codex as a coding partner. This is a living tutorial: the project is small on purpose, but it now has tabs, drag‑drop, toolbar actions, and basic syntax coloring.

Why This Matters
AmigaOS 4.1 isn’t exactly mainstream — which makes it a perfect target for AI‑assisted development. Codex helped with platform‑specific MUI patterns, pulling from OS4 SDK examples, and cleaning up builds and runtime behavior. The result is a working editor and a documented path that others can follow.

What We Built

  • MUI app scaffold + menus
  • TextEditor.mcc integration
  • File open/save with ASL
  • Tabs for multiple files
  • Clipboard history
  • Drag‑and‑drop file open
  • Theme switching + recolor pass
  • A growing README + concept docs

Example Prompt (for your own project)

You are Codex acting as a coding partner for AmigaOS 4.1 MUI development.
Stay inside the OS4 SDK and its Examples folder; avoid AROS/OS3.1 snippets.
Build a minimal text editor using TextEditor.mcc with:
- menu actions (Open/Save/Copy/Paste/Undo/Recolor)
- tabs via RegisterObject
- ASL file requester
- drag-and-drop file open
- simple syntax coloring for C
Keep everything in main.c with clear helper sections, and add a README
explaining the flow + build instructions (docker cross-compile).

When errors appear, fix them in small steps and explain why.
Prefer OS4 interfaces and proper library open/close patterns.

Workflow Notes (practical details)
We kept the workflow tight and repeatable:

  • Target OS: AmigaOS 4.1 Final (fully updated) on A1222
  • Tools on Amiga: CodeBench, SGrab, and Pete’s FTP
  • SDK: Official OS4 SDK (local, with Examples used as primary references)
  • Cross‑compile: Docker container rolfkopman/os4env

Cross‑compile command

sudo docker run --rm -v /home/auzieman/Projects:/Projects \
  rolfkopman/os4env /bin/bash -lc "cd /Projects/AmiWriterMUI && make clean && make"

File transfer (Linux <-> Amiga)
We used FTP to move binaries and screenshots quickly:

  1. Run Pete’s FTP on AmigaOS 4.1
  2. From Linux, push/pull the project folder or just the built binary
  3. Test on hardware, then sync back screenshots and notes

This kept the loop fast: build on Linux, test on real hardware, document results.

Debugging (GDB quick notes)
When something crashed or behaved oddly, we used GDB on target:

gdb --args AmiWriterMUI
run

If it crashes:

bt full

To capture a full backtrace to a file for review:

set logging file gdb_bt.txt
set logging on
bt full
set logging off

Then copy gdb_bt.txt back to Linux for analysis and keep iterating.

Screenshots

SDK Walkthrough (quick build‑up)
This isn’t every line of code, but it shows the order we assembled the app — like the old magazine “build it up” articles.

1) Open OS4 libraries + interfaces
We keep the OS4 pattern: open libraries first, grab interfaces, and cleanly close them later.

static BOOL open_libraries(void)
{
    MUIMasterBase = OpenLibrary("muimaster.library", 20);
    IMUIMaster = (struct MUIMasterIFace *)GetInterface(MUIMasterBase, "main", 1, NULL);

    IntuitionBase = (struct IntuitionBase *)OpenLibrary("intuition.library", 50);
    IIntuition = (struct IntuitionIFace *)GetInterface((struct Library *)IntuitionBase, "main", 1, NULL);

    AslBase = OpenLibrary("asl.library", 50);
    IAsl = (struct AslIFace *)GetInterface(AslBase, "main", 1, NULL);

    DOSBase = (struct DosLibrary *)OpenLibrary("dos.library", 50);
    IDOS = (struct DOSIFace *)GetInterface((struct Library *)DOSBase, "main", 1, NULL);
    return TRUE;
}

2) Create the editor and its scrollbar
TextEditor.mcc drives the edit area. We attach a vertical prop via MUIA_TextEditor_Slider so scrolling works correctly.

APTR vprop = PropObject, PropFrame,
    MUIA_Prop_Horiz, FALSE,
    MUIA_FixWidth, 10,
End;

APTR editor = TextEditorObject,
    MUIA_TextEditor_FixedFont, TRUE,
    MUIA_TextEditor_WrapMode,  TRUE,
    MUIA_TextEditor_Slider, vprop,
End;

3) Build the window layout
Toolbar on top, tab register in the middle, status line at the bottom.

app = ApplicationObject,
    MUIA_Application_Menustrip, MUI_MakeObject(MUIO_MenustripNM, menuBar, MUIO_MenustripNM_CommandKeyCheck),
    SubWindow, window = WindowObject,
        WindowContents, VGroup,
            Child, HGroup,  /* toolbar */
            Child, RegisterObject,  /* tabs */
            Child, status_text,     /* status */
        End,
    End,
End;

4) Wire menu + toolbar actions
We use MUI notifies to funnel actions into the input loop (Open/Save/Copy/Paste/Undo/Recolor).

DoMethod(app, MUIM_Notify, MUIA_Application_MenuAction, MEN_OPEN,
    app, 2, MUIM_Application_ReturnID, MEN_OPEN);

DoMethod(btn_save, MUIM_Notify, MUIA_Pressed, FALSE,
    app, 2, MUIM_Application_ReturnID, MEN_SAVE);

5) File open/save with ASL
Use an ASL requester to fetch a path, then load/save with plain C file IO.

if (pick_file("Open file", FALSE, path, sizeof(path)))
    load_file_into_tab(tab, path);

6) Colorize when needed
The colorizer is intentionally simple: scan text line‑by‑line, set blocks for keywords/strings/comments, and keep it predictable.

apply_syntax_colors(editor);
set(editor, MUIA_TextEditor_ColorMap, color_map);

That’s the core flow: open libs, build the UI, wire actions, then iterate on features and polish.

Repo
Source and notes are here:
https://dtlab.auzietek.com/auzieman/AmiWriterMUI

What’s Next
We’ll keep refining color palettes, improve recolor performance, and continue adding editor ergonomics (shortcuts, maybe tabs/toolbar polish). The goal is a clear tutorial‑style codebase that new AmigaOS 4.1 developers can actually learn from.

Credits & Thanks
Big thanks to the AmigaOS 4.1 ecosystem that keeps development alive:

Blog tags
AmigaOS4.1
gcc
MUI
gui
development
Submitted by auzieman on Sat, 12/20/2025 - 15:27