Always limit Magnifying glass's height

MagnifyingGlass::sizeUp() and MagnifyingGlass::sizeDown() grow/shrink
both width and height, but check only width's limits. Thus the user can
first increase Magnifying glass's height, then increase its size and
make the height greater than the main window's height. The user can also
first increase the width, then decrease the size until the height
shrinks to 0 and Magnifying glass disappears.

When Magnifying glass disappears, the only way to make it visible again
is to restore its default size by restarting YACReader, because the
invisible MagnifyingGlass widget does not receive wheel events and
Viewer::keyPressEvent() propagates shortcuts to mglass only if it is
visible. And even this workaround is possible only because YACReader
does not save/restore Magnifying glass's size (should it?).

Always checking both width and height limits fixes the bug. If one of
the dimensions reaches a limit, only the other dimension is modified. If
both dimensions reach their limits, neither is modified.

YACReader/magnifying_glass.cpp

@@ -191,42 +191,48 @@ void MagnifyingGlass::zoomOut()
     }
 }
 
-static constexpr auto maxRelativeDimension = 0.9;
-
 void MagnifyingGlass::sizeUp()
 {
-    if (width() < parentWidget()->width() * maxRelativeDimension)
-        resizeAndUpdate(width() + 30, height() + 15);
+    auto w = width();
+    auto h = height();
+    if (growWidth(w) | growHeight(h)) // bitwise OR prevents short-circuiting
+        resizeAndUpdate(w, h);
 }
 
 void MagnifyingGlass::sizeDown()
 {
-    if (width() > 175)
-        resizeAndUpdate(width() - 30, height() - 15);
+    auto w = width();
+    auto h = height();
+    if (shrinkWidth(w) | shrinkHeight(h)) // bitwise OR prevents short-circuiting
+        resizeAndUpdate(w, h);
 }
 
 void MagnifyingGlass::heightUp()
 {
-    if (height() < parentWidget()->height() * maxRelativeDimension)
-        resizeAndUpdate(width(), height() + 15);
+    auto h = height();
+    if (growHeight(h))
+        resizeAndUpdate(width(), h);
 }
 
 void MagnifyingGlass::heightDown()
 {
-    if (height() > 80)
-        resizeAndUpdate(width(), height() - 15);
+    auto h = height();
+    if (shrinkHeight(h))
+        resizeAndUpdate(width(), h);
 }
 
 void MagnifyingGlass::widthUp()
 {
-    if (width() < parentWidget()->width() * maxRelativeDimension)
-        resizeAndUpdate(width() + 30, height());
+    auto w = width();
+    if (growWidth(w))
+        resizeAndUpdate(w, height());
 }
 
 void MagnifyingGlass::widthDown()
 {
-    if (width() > 175)
-        resizeAndUpdate(width() - 30, height());
+    auto w = width();
+    if (shrinkWidth(w))
+        resizeAndUpdate(w, height());
 }
 
 void MagnifyingGlass::resizeAndUpdate(int w, int h)
@@ -235,6 +241,46 @@ void MagnifyingGlass::resizeAndUpdate(int w, int h)
     updateImage();
 }
 
+static constexpr auto maxRelativeDimension = 0.9;
+static constexpr auto widthStep = 30;
+static constexpr auto heightStep = 15;
+
+bool MagnifyingGlass::growWidth(int &w) const
+{
+    const auto maxWidth = parentWidget()->width() * maxRelativeDimension;
+    if (w >= maxWidth)
+        return false;
+    w += widthStep;
+    return true;
+}
+
+bool MagnifyingGlass::shrinkWidth(int &w) const
+{
+    constexpr auto minWidth = 175;
+    if (w <= minWidth)
+        return false;
+    w -= widthStep;
+    return true;
+}
+
+bool MagnifyingGlass::growHeight(int &h) const
+{
+    const auto maxHeight = parentWidget()->height() * maxRelativeDimension;
+    if (h >= maxHeight)
+        return false;
+    h += heightStep;
+    return true;
+}
+
+bool MagnifyingGlass::shrinkHeight(int &h) const
+{
+    constexpr auto minHeight = 80;
+    if (h <= minHeight)
+        return false;
+    h -= heightStep;
+    return true;
+}
+
 void MagnifyingGlass::keyPressEvent(QKeyEvent *event)
 {
     bool validKey = false;

YACReader/magnifying_glass.h

@@ -13,6 +13,15 @@ private:
     float zoomLevel;
     void setup(const QSize &size);
     void resizeAndUpdate(int w, int h);
+
+    // The following 4 functions increase/decrease their argument and return true,
+    // unless the maximum dimension value has been reached, in which case they
+    // do not modify the argument and return false.
+    bool growWidth(int &w) const;
+    bool shrinkWidth(int &w) const;
+    bool growHeight(int &h) const;
+    bool shrinkHeight(int &h) const;
+
     void keyPressEvent(QKeyEvent *event) override;
 
 public: