  HEALPix by G\'orski et. al. (2005) is de-facto standard for Cosmic Microwave
Background (CMB) data storage and analysis, and is widely used in current and
upcoming CMB experiments. Almost all the datasets in Legacy Archive for
Microwave Background Data Analysis (LAMBDA) use HEALPix as a format of choice.
Visualizing the data plays important role in research, and several toolsets
were developed to do that with HEALPix maps, most notably original Fortran
facilities and Python integration with healpy.
  With the current state of GPU performance, it is now possible to visualize
extremely large maps in real time on a laptop or a tablet. HEALPix Viewer
described here is developed for macOS, and takes full advantage of GPU
acceleration to handle extremely large datasets in real time. It compiles
natively on Intel and Arm64 architectures, and uses Metal framework for
high-performance GPU computations. The aim of this project is to reduce the
effort required for interactive data exploration, as well as time overhead for
producing publication-quality maps. Drag and drop integration with Keynote and
Powerpoint makes creating presentations easy.
  The main codebase is written in Swift, a modern and efficient compiled
language, with high-performance computing parts delegated entirely to GPU, and
a few inserts in C interfacing to cfitsio library for I/O. Graphical user
interface is written in SwiftUI, a new declarative UI framework based on Swift.
Most common spherical projections and colormaps are supported out of the box,
and the available source code makes it easy to customize the application and to
add new features if desired. Overall performance improves on the current Python
software stack by a factor of 3-180x depending on the task at hand.
