Why does macOS prefer using PDF files for icons or UI elements?
2 damiaozi 2 5/15/2025, 9:41:30 AM
Running `find /System/Library/ -name "*.pdf"` reveals that macOS uses many .pdf files as icons or UI elements. For example, the VPN connection animation in the menu bar seems to cycle through a sequence of .pdf files located at:
/System/Library/CoreServices/Menu Extras/VPN.menu/Contents/Resources/VPN[0-4].pdf
Why PDF, instead of more traditional formats like PNG or SVG? Is this due to Quartz/CoreGraphics rendering benefits, vector scaling efficiency, or something else?
And to add to it: macOS (and its derivatives, such as iOS) descends from an operating system called OPENSTEP (formerly NeXTSTEP), which used Display Postscript for on-screen rendering.
Apple later replaced Display PostScript with a more modern reimplementation called Quartz 2D[1], which switched from Postscript to PDF.
Why not PNG? Because PNG is a bitmap format and Quartz 2D is designed to be resolution-independent.
Why not SVG? Probably because Quartz 2D relies heavily on the PDF specification throughout and it would be too much work to reimplement, and for what? PDF is still a common and well-regarded format.
1. https://en.wikipedia.org/wiki/Quartz_2D