[okular] [Bug 443404] Mousewheel scroll does not work in full page size and non-continous mode for some mouses

[Zack]

https://bugs.kde.org/show_bug.cgi?id=443404

--- Comment #11 from Zack <smallmak113 at gmail.com> ---
I looked into the source code and added few lines to the pageview.cpp to handle
the small "delta" value reported in the PageView::wheelEvent for my mice. And
now I could scroll in pages in full page view and non-continous mode. (only
tested on libinput mode but not in evdev mode)

I don't know how I should request code change. Here's the few lines that I
added. Maybe the developers see this and test it or possibly merge into the
main branch.

--- okular-21.12.3/part/pageview_orig.cpp       2022-02-28 02:11:02.000000000
+0800
+++ okular-21.12.3/part/pageview.cpp    2022-07-19 00:07:04.332931401 +0800
@@ -3170,22 +3170,32 @@
     if ((e->modifiers() & Qt::ControlModifier) == Qt::ControlModifier) {
         d->controlWheelAccumulatedDelta += delta;
         if (d->controlWheelAccumulatedDelta <=
-QWheelEvent::DefaultDeltasPerStep) {
             slotZoomOut();
             d->controlWheelAccumulatedDelta = 0;
         } else if (d->controlWheelAccumulatedDelta >=
QWheelEvent::DefaultDeltasPerStep) {
             slotZoomIn();
             d->controlWheelAccumulatedDelta = 0;
         }
     } else {
-        d->controlWheelAccumulatedDelta = 0;
-
+        if (d->controlWheelAccumulatedDelta * delta < 0) {
+            d->controlWheelAccumulatedDelta = 0;
+        }
+        d->controlWheelAccumulatedDelta += delta;
+        if (abs(d->controlWheelAccumulatedDelta) >=
QWheelEvent::DefaultDeltasPerStep){
+            delta = d->controlWheelAccumulatedDelta > 0 ?
QWheelEvent::DefaultDeltasPerStep : -QWheelEvent::DefaultDeltasPerStep;
+            d->controlWheelAccumulatedDelta = 0;
+        }
+        else {
+            delta = 0;
+        }
+        
         if (delta <= -QWheelEvent::DefaultDeltasPerStep &&
!getContinuousMode() && vScroll == verticalScrollBar()->maximum()) {
             // go to next page
             if ((int)d->document->currentPage() < d->items.count() - 1) {
                 // more optimized than document->setNextPage and then move
view to top
                 Okular::DocumentViewport newViewport =
d->document->viewport();
                 newViewport.pageNumber += viewColumns();
                 if (newViewport.pageNumber >= (int)d->items.count())
                     newViewport.pageNumber = d->items.count() - 1;
                 newViewport.rePos.enabled = true;
                 newViewport.rePos.normalizedY = 0.0;

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