TweakPNG

Native macOS port of TweakPNG for viewing and editing PNG chunk metadata, while keeping the original project source in this repository.

This repository now contains two parts:

• the original Windows TweakPNG source in the repository root
• a native macOS app built with SwiftUI/AppKit and a reusable C++ PNG core

Requirements

Runtime and build requirements for the macOS port:

• macOS 13 or newer
• Xcode Command Line Tools
• Swift 6 toolchain (swift)
• uv for the packaging helper environment
• Python 3.12 for the icon-generation helper managed by uv

Optional tools used by packaging:

• iconutil
• codesign
• hdiutil

Repository layout

• Sources/TweakPNGCore - portable C++ PNG parsing and editing layer
• Sources/TweakPNGMac - native macOS UI
• macos/build-app.sh - app bundle, zip, and dmg packaging script
• macos/tools - uv-managed Python helper for icon generation
• macos/Assets/AppIconSource.png - source image used for the macOS app icon
• root *.cpp / *.h files - original Windows codebase

Development build

Build the macOS app:

swift build

Run it directly from SwiftPM:

swift run TweakPNG

Release build

Build an optimized executable:

swift build -c release

The executable is emitted at:

• .build/release/TweakPNG

Packaging

Create a local distributable app bundle, zip archive, and dmg:

chmod +x macos/build-app.sh
./macos/build-app.sh

Packaging outputs:

• dist/TweakPNG.app
• dist/TweakPNG-macos.zip
• dist/TweakPNG.dmg
• dist/TweakPNG.dSYM

The packaging flow does the following:

1. creates or reuses the uv Python environment in macos/tools
2. generates a macOS .iconset from macos/Assets/AppIconSource.png
3. converts the iconset into AppIcon.icns
4. builds the Swift release executable
5. assembles the .app bundle
6. applies ad-hoc signing by default
7. emits a .zip and .dmg

Signing

This repository is currently configured to work without a paid Apple Developer certificate. By default, the packaging script performs ad-hoc signing so the app can still be built and shared for local testing.

If you later install a real signing identity, you can override the signer:

SIGN_IDENTITY="Developer ID Application: GamerNoTitle" ./macos/build-app.sh

Without a real Developer ID certificate and notarization, macOS may warn users on first launch. That is expected for the current release flow.

Dependencies

Project dependencies by layer:

• TweakPNGCore
  • C++17
  • system zlib
• TweakPNG
  • SwiftUI
  • AppKit
  • Swift/C++ interoperability
• macos/tools
  • Python 3.12
  • Pillow

Current macOS feature set

• open PNG files
• inspect chunk rows with type, length, CRC, attributes, and summary
• preview the current image in a native macOS inspector pane
• add tEXt chunks
• delete and reorder chunks
• save and save as
• package as .app, .zip, and .dmg

Notes

• The original Windows code is intentionally preserved and remains in the repo.
• The macOS port is a native implementation, not a Win32 compatibility layer.
• Some advanced Windows-era editing dialogs and chunk-specific editors are not yet ported.

Credit

• Original TweakPNG project by Jason Summers
• Original project page: https://entropymine.com/jason/tweakpng/
• Original source repository: https://github.com/jsummers/tweakpng