On macOS arm64 (Apple Silicon, Sequoia), exporting a PDF via
QPrintPreviewWidget leaves a black screen with only the mouse cursor
visible. Cmd+Tab restores the display; the exported PDF itself is
correct and clickable cross-reference links work fine.
Root cause
----------
requestPaint() is a slot connected to QPrintPreviewWidget::paintRequested.
Inside this slot the code was calling painter.end() manually, then
pdfConvertUriToGoTo(). On macOS arm64 the Qt5 paint cycle backed by
Metal/CALayer is asynchronous: closing the QPainter from *within* the
paintRequested slot interrupts the compositor before it has flushed the
backing store. The window goes black and never repaints because the
close() that follows immediately destroys it.
On x86_64 / older macOS (raster/CoreGraphics backend) the paint cycle is
synchronous, so the same code happened to work.
Fix
---
1. Remove the manual painter.end() and pdfConvertUriToGoTo() call from
requestPaint(). The QPainter is stack-allocated; it destructs normally
when the slot returns, which is the correct moment to flush the PDF.
2. In print(), capture the output file name before m_preview->print(),
then defer both pdfConvertUriToGoTo() and this->close() to the next
event-loop iteration via QTimer::singleShot(0, ...). This gives the
Metal compositor one full event-loop turn to finish compositing the
backing store before the window is torn down.
The fix is a no-op on all other platforms: QTimer::singleShot(0) posts
an event that fires in the very next iteration, so there is no perceptible
delay.
Tested
------
- macOS Sequoia 15.x, Apple M-series, Qt 5.15.x (arm64): black screen gone
- macOS 10.15 x86_64 VM, Qt 5.15.x: no regression
- Linux/Debian Qt 5.15.x: no regression
- PDF cross-reference links and GoTo/FitR destinations: unaffected
Fixes: black screen after PDF export on macOS arm64
Laurent Trinques
2b7e62f901