The hovered "d = ... A" readout was a QGraphicsTextItem flagged
ItemIgnoresTransformations, repositioned on every mouse motion. Qt cannot
compute a tight dirty rect for an item that ignores the view transform, so it
marks the entire viewport dirty whenever such an item moves or changes text --
and this one moved constantly.
Paint it in drawForeground() in viewport pixels instead, and repaint only the
union of its old and new rectangles. That also removes the item lifetime
special-casing: it was deliberately kept out of overlay_items_, had to be
nulled by hand after scene()->clear(), and carried comments in three places
warning about the dangling pointer.
This does not reduce raw X11 traffic -- there every repaint uploads the whole
window whatever the damage -- but it cuts the work per hover, and it does
matter under a compressing remote protocol (VNC/NX/xpra), which encodes only
the region that actually changed.
Verified against the previous build: same text, colour and position.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
leonarski_fandClaude Opus 5
4892c57119