Step toward building jfjoch_viewer on Windows/MSVC. No change to the Linux
build: D-Bus stays on by default and the XCB plugin is still used.
- CMake: make Qt6::DBus optional via JFJOCH_VIEWER_DBUS (ON on Linux, OFF on
Windows/macOS where Qt6::DBus does not exist); compile/link/install the dbus/
adaptor + service file only when enabled. Select the platform integration
plugin per-OS (QXcb on Linux, QWindows on Windows, QCocoa on macOS) instead
of hard-coding QXcbIntegrationPlugin.
- JFJochViewerWindow: wrap the adaptor include and D-Bus registration in
#ifdef JFJOCH_VIEWER_DBUS.
- JFJochImageReadingWorker: the POSIX open()/fstat()/NFS-errno preflight is now
#ifndef _WIN32, with a portable QFileInfo fallback elsewhere; POSIX-only
headers are guarded too.
- Replace the POSIX M_PI/M_PI_2 extension with C++20 std::numbers::pi across the
viewer (not defined by MSVC without _USE_MATH_DEFINES).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>