qtfb: fix scaled partial updates collapsing to empty rects - #66
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dcasselwork123 wants to merge 1 commit into
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qtfb: fix scaled partial updates collapsing to empty rects#66dcasselwork123 wants to merge 1 commit into
dcasselwork123 wants to merge 1 commit into
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FBController::markedUpdate computed the scaled update rect with integer division (rect.x() / image->width() == 0 for any x inside the image), so every partial update on an allowScaling canvas requested an empty repaint and the screen never changed; only MESSAGE_UPDATE/UPDATE_ALL repainted. Scale with qreal instead, flooring the origin and ceiling the size (+1px slop) so the damaged area is always covered. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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The bug
FBController::markedUpdate(const QRect&)computes the scaled repaint rect with integer division:(rect.x() / image->width()) * this->width()For any rect inside the framebuffer,
rect.x() / image->width()is0(and likewise the width/height terms), so on anallowScaling: truecanvas every partial update requests an empty repaint. Clients that useMESSAGE_UPDATE/UPDATE_PARTIALrender into the SHM correctly but the screen never changes; onlyUPDATE_ALL(which callsmarkedUpdate()with no rect) repaints.Observed on a reMarkable 2 (OS 3.27.1, AppLoad v0.5.3) with a native qtfb client: the app's initial full update painted, then all subsequent partial updates were silently dropped. Working around it client-side with
UPDATE_ALLper stroke makes writing latency unusable on the GPU-less rM2, since each update becomes a full-window software repaint.The fix
Scale in
qreal, flooring the origin and ceiling the size with 1px slop so the damaged area is always covered. Also guards against a zero-sized image.Tested on the rM2: partial updates repaint correctly and pen latency with a 35 ms update cadence is good.
🤖 Generated with Claude Code