Pinch to zoom causes page to jump

[Evidlo]

Occasionally when I pinch to zoom Write will jump to the next/prev page. I'm not sure if I'm triggering some gesture that I don't know about. Below is a video of the behavior.

styluslabswrite_jump4.1.mp4

Build 19277c8, Dec 9 2024

[Evidlo]

I think I have a rough idea how to replicate this (and maybe why it happens?). I used Claude to help figure this out, but it makes sense to me:

1. Start on some page (e.g. currPage is 5)
2. Scroll down so that page 5 is mostly off the viewport, but not enough to trigger the page change detection in ScribbleArea::doPan (previous page needs to overlap viewport shrunk by 1/6)

Write/syncscribble/scribblearea.cpp

Lines 257 to 269 in 6f3330c

	// shrink screenrect so page changes before prev page is completely invisible
	screenrect.pad(-screenrect.width()/6, -screenrect.height()/6);
	if(!pagerect.overlaps(screenrect)) {
	int firstvispage = dimToPageNum(Point(screenrect.left, screenrect.top));
	if(currPageNum < firstvispage)
	setPageNum(firstvispage);
	else {
	int lastvispage = dimToPageNum(Point(screenrect.right, screenrect.bottom));
	if(currPageNum > lastvispage)
	setPageNum(lastvispage);
	else
	return;
	}

3. Two-finger zoom so that zoom is within 10% of fit-height, triggering setCenterPos, which centers on page 5 even though page 6 is the one thats visible

Write/syncscribble/scribblearea.cpp

Lines 236 to 247 in 6f3330c

	if(mZoom == 1) {}
	else if(wzoom < 1.1*zoom && zoom < 1.1*wzoom && (wzoom > 1.05 || wzoom < 0.95)) {
	Point currCorner = screenToDim(Point(0, 0));
	Point pageCorner = pageDimToDim(Point(0, 0));
	zoomTo(wzoom, px, py);
	setCornerPos(Point(pageCorner.x - xborder/mScale, currCorner.y));
	}
	else if(hzoom < 1.1*zoom && zoom < 1.1*hzoom && (hzoom > 1.05 || hzoom < 0.95)) {
	setZoom(hzoom);
	setCenterPos(pageDimToDim(Point(currPage->width()/2, currPage->height()/2)));
	}
	}

In the video I'm able to jump back/forth between two pages a few times while zooming, which doesn't entirely make sense to me from the above explanation. It's clearly something to do with page detection logic and snapping though.