Qt: Fix click to packet on OverlayScrollBar

Fix the calculation of the ratio for converting a packet number
to the scrollbar value by accounting for the length of the slider.
maximum() does not correpond to the last packet; it corresponds to
the first packet shown when the scrollbar is at maximum. The last
packet is maximum() + pageStep().
(See https://doc.qt.io/qt-6/qscrollbar.html#details)

The quarter of a page padding should be subtracted, not added,
from the calculated position.
(Fix up 422c0f45d497872a963363132ec92d400a79538f)

This correctly makes clicking on the a line in the minimap scroll
the packet list so that the corresponding packet is 25% of the
way down the visible window. (Excepting the cases of packets at
the very beginning or end of the entire packet list.)

Fix #13989

1 files changed, 7 insertions, 2 deletions

diff --git a/ui/qt/widgets/overlay_scroll_bar.cpp b/ui/qt/widgets/overlay_scroll_bar.cpp
index c3262c6220..8a734c6892 100644
--- a/ui/qt/widgets/overlay_scroll_bar.cpp
+++ b/ui/qt/widgets/overlay_scroll_bar.cpp
@@ -241,9 +241,14 @@ void OverlayScrollBar::mouseReleaseEvent(QMouseEvent *event)
     if (pm_r.contains(event->pos()) && geometry().height() > 0 && packet_count_ > 0 && pageStep() > 0) {
         double map_ratio = double(end_pos_ - start_pos_) / geometry().height();
         int clicked_packet = (event->pos().y() * map_ratio) + start_pos_;
-        double packet_to_sb_value = double(maximum() - minimum()) / packet_count_;
+        /* The first packet is at minimum(). The last packet is at
+         * maximum() + pageStep(). (maximum() corresponds to the first
+         * packet shown when the scrollbar at at the maximum position.)
+         * https://doc.qt.io/qt-6/qscrollbar.html#details
+         */
+        double packet_to_sb_value = double(maximum() + pageStep() - minimum()) / packet_count_;
         int top_pad = pageStep() / 4; // Land near, but not at, the top.
 
-        setValue((clicked_packet * packet_to_sb_value) + top_pad);
+        setValue((clicked_packet * packet_to_sb_value) - top_pad);
     }
 }