Research how we could support generating .ico, .icns files at build time.

Why?

.icns and .ico files are both binary files used for representing icons in different resolutions. As such, they can be generated on the fly from image files in different resolutions. Allowing the user to generate them, e.g., from .png files on the fly, would make it easier to update single-resolution files or add new resolution files. In particular, it would also allow sharing images between macOS and iOS bundles (iOS allows for packaging image files in the form of an .xcassets folder).

Options

icns: Using xcrun actool

Qt Creator does generate its .icns file on macOS from a .xcasset directory using native command line tools :

  add_custom_command(
    OUTPUT qtcreator.icns qtcreator-project.icns
    COMMAND
      xcrun actool --app-icon qtcreator --output-partial-info-plist "${CMAKE_CURRENT_BINARY_DIR}/qtcreator.Info.plist"
      --platform macosx --minimum-deployment-target 10.7 --compile "${CMAKE_CURRENT_BINARY_DIR}"
      "${IDE_ICON_PATH}/qtcreator.xcassets"
      > /dev/null
    BYPRODUCTS qtcreator.Info.plist
    DEPENDS
      qtcreator.xcassets/qtcreator.appiconset/Contents.json
      qtcreator.xcassets/qtcreator.appiconset/icon_128x128.png
      ...

icns: Using iconutil tool

This is the command-line tool recommended in the current Qt documentation. It processes .iconset folders.

.ico: Using ImageMagick

ImageMagick is commonly used to create .ico files on Windows.

Using a Qt native tool

Qt imageformats does support both .icns and .ico files. Can we provide our own cross-platform binary tool to generate .ico and .icns files?