Panning called updateOverlay() three times per mouse move: once for each
scrollbar's valueChanged -> onScroll(), then once explicitly. Zooming was the
same. Every one of those tore down and rebuilt every overlay item.
Suppress onScroll() for the duration of the gesture instead, and let the
gesture do its single rebuild at the end. Note this cannot be done by blocking
the scrollbars' signals: QAbstractScrollArea drives the actual scrolling off
valueChanged, so blocking it would stop the view moving at all.
updateOverlay() also refreshed the image item unconditionally, which marks the
whole item dirty and forces a full-viewport repaint even though pan and zoom
never change the pixels. Track whether RenderImage has run since the last
refresh and skip it otherwise.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
leonarski_fandClaude Opus 5
c3eba650e9