Improve sizing and scrolling of the unit choice popup

The unit selection popup for stacks in the open (and in allied cities)
didn't behave very well with many units: its width remained fixed to 4
and it was showing at most 12 units -- quite a small stack for a serious
attack. In addition, the last row was in some cases inaccessible due to
a scrolling bug (maybe Wayland-specific; #2285).

Increase the base width of the menu to 5 units (a loaded Galleon), and
further to 6 when there are more than 25 units. Show up to 36 units
(four fully loaded Transports) at once before resorting to scrolling.

Fix the scrolling bug, which was related to scroll events with deltaY=0
being interpreted as scrolling upwards.

Closes #2285.

client/unitselect.cpp

@@ -98,20 +98,16 @@ void units_select::create_pixmap()
     delete h_pix;
     h_pix = new QPixmap(item_size.width(), item_size.height());
     h_pix->fill(palette().color(QPalette::HighlightedText));
-    if (unit_count < 5) {
-      row_count = 1;
-      pix = new QPixmap((unit_list.size()) * item_size.width(),
-                        item_size.height());
-    } else if (unit_count < 9) {
-      row_count = 2;
-      pix = new QPixmap(4 * item_size.width(), 2 * item_size.height());
-    } else {
-      row_count = 3;
-      if (unit_count > 12) {
-        more = true;
-      }
-      pix = new QPixmap(4 * item_size.width(), 3 * item_size.height());
-    }
+
+    // Determine the layout. 5 columns up to 25 units, then 6.
+    column_count = qMin(unit_count, unit_count <= 25 ? 5 : 6);
+    // Up to 6 rows visible at the same time.
+    row_count = qMin((unit_count + column_count - 1) / column_count, 6);
+    // And whether we go over.
+    more = unit_count > row_count * column_count;
+
+    pix = new QPixmap(column_count * item_size.width(),
+                      row_count * item_size.height());
     pix->fill(Qt::transparent);
     for (auto *punit : qAsConst(unit_list)) {
       unit_pixmap = new QPixmap(tileset_unit_width(tileset),
@@ -147,7 +143,7 @@ void units_select::create_pixmap()
     while (!pix_list.isEmpty()) {
       tmp_pix = pix_list.takeFirst();
       i++;
-      if (i % 4 == 0) {
+      if (i % column_count == 0) {
         x = 0;
         y = y + item_size.height();
       }
@@ -200,7 +196,7 @@ void units_select::mouseMoveEvent(QMouseEvent *event)
   } else if (row_count > 0) {
     a = (event->x() - 10) / item_size.width();
     b = (event->y() - fm.height() - 3) / item_size.height();
-    highligh_num = b * 4 + a;
+    highligh_num = b * column_count + a;
   }
   if (old_h != highligh_num) {
     create_pixmap();
@@ -281,7 +277,7 @@ void units_select::paint(QPainter *painter, QPaintEvent *event)
     }
     // draw scroll
     if (more) {
-      int maxl = ((unit_count - 1) / 4) + 1;
+      int maxl = ((unit_count - 1) / column_count) + 1;
       float page_height = 3.0f / maxl;
       float page_start = (static_cast<float>(show_line)) / maxl;
       pen.setColor(palette().color(QPalette::HighlightedText));
@@ -339,7 +335,7 @@ void units_select::update_units()
       unit_list_iterate(utile->units, punit)
       {
         unit_count++;
-        if (i > show_line * 4) {
+        if (i > show_line * column_count) {
           unit_list.push_back(punit);
         }
         i++;
@@ -366,16 +362,22 @@ void units_select::closeEvent(QCloseEvent *event)
  */
 void units_select::wheelEvent(QWheelEvent *event)
 {
-  int nr;
-
   if (!more && utile == nullptr) {
     return;
   }
-  nr = qCeil(static_cast<qreal>(unit_list_size(utile->units)) / 4) - 3;
-  if (event->angleDelta().y() < 0) {
+
+  // The number of hidden lines. This is the number of rows needed to show
+  // all units, minus what is shown without scrolling.
+  auto nr = (unit_list_size(utile->units) + column_count - 1) / column_count
+            - row_count;
+
+  // We scroll one full row per scroll event. The angle delta determines the
+  // direction in which we scroll. We don't scroll when it's 0.
+  const auto delta = event->angleDelta().y();
+  if (delta < 0) {
     show_line++;
     show_line = qMin(show_line, nr);
-  } else {
+  } else if (delta > 0) {
     show_line--;
     show_line = qMax(0, show_line);
   }

client/unitselect.h

@@ -33,7 +33,7 @@ class units_select : public QMenu {
                             * iterate utile->units */
   QFont ufont;
   QFont info_font;
-  int row_count;
+  int column_count, row_count;
 
 public:
   units_select(struct tile *ptile, QWidget *parent = 0);