viewersizer: use float for all calculations, center manual zoom

app/widget/viewer/viewer.cpp

@@ -1376,10 +1376,10 @@ void ViewerWidget::ShowContextMenu(const QPoint &pos)
       Menu* zoom_menu = new Menu(tr("Zoom"), &menu);
       menu.addMenu(zoom_menu);
 
-      zoom_menu->addAction(tr("Fit"))->setData(0);
+      zoom_menu->addAction(tr("Fit"))->setData(-1);
       for (int i=0;i<ViewerSizer::kZoomLevelCount;i++) {
-        int z = ViewerSizer::kZoomLevels[i];
-        zoom_menu->addAction(tr("%1%").arg(z))->setData(z);
+        double z = ViewerSizer::kZoomLevels[i];
+        zoom_menu->addAction(tr("%1%").arg(z * 100.0))->setData(z);
       }
 
       connect(zoom_menu, &QMenu::triggered, this, &ViewerWidget::SetZoomFromMenu);
@@ -1822,7 +1822,8 @@ void ViewerWidget::UpdateRendererAudioParameters()
 
 void ViewerWidget::SetZoomFromMenu(QAction *action)
 {
-  sizer_->SetZoom(action->data().toInt());
+  auto s = sizer_->GetContainerSize();
+  sizer_->SetZoomAnchored(action->data().toDouble(), s.width()/2, s.height()/2);
 }
 
 void ViewerWidget::ViewerInvalidatedVideoRange(const TimeRange &range)

app/widget/viewer/viewersizer.cpp

@@ -35,7 +35,7 @@ ViewerSizer::ViewerSizer(QWidget *parent) :
   width_(0),
   height_(0),
   pixel_aspect_(1),
-  zoom_(0),
+  zoom_(-1),
   current_widget_scale_(0)
 {
   horiz_scrollbar_ = new QScrollBar(Qt::Horizontal, this);
@@ -64,6 +64,12 @@ void ViewerSizer::SetWidget(QWidget *widget)
   }
 }
 
+QSize ViewerSizer::GetContainerSize() const
+{
+  double s = GetRealCurrentZoom();
+  return QSize(std::min(this->width(), int(width_ * s)) - vert_scrollbar_->width(), std::min(int(height_ * s), this->height()) - horiz_scrollbar_->height());
+}
+
 void ViewerSizer::SetChildSize(int width, int height)
 {
   width_ = width;
@@ -79,13 +85,36 @@ void ViewerSizer::SetPixelAspectRatio(const rational &pixel_aspect)
   UpdateSize();
 }
 
-void ViewerSizer::SetZoom(int percent)
+void ViewerSizer::SetZoom(double percent)
 {
   zoom_ = percent;
 
   UpdateSize();
 }
 
+void ViewerSizer::SetZoomAnchored(double next_scale, double cursor_x, double cursor_y)
+{
+  if (next_scale > 0) {
+    double cur_scale = GetRealCurrentZoom();
+
+    // Clamp scale within safe values
+    next_scale = std::clamp(next_scale, kZoomLevels[0], kZoomLevels[kZoomLevelCount-1]);
+
+    int anchor_x = qRound(double(cursor_x + horiz_scrollbar_->value()) / cur_scale * next_scale - cursor_x);
+    int anchor_y = qRound(double(cursor_y + vert_scrollbar_->value()) / cur_scale * next_scale - cursor_y);
+
+    SetZoom(next_scale);
+
+    horiz_scrollbar_->setValue(anchor_x);
+    vert_scrollbar_->setValue(anchor_y);
+  } else {
+    SetZoom(-1);
+
+    horiz_scrollbar_->setValue(0);
+    vert_scrollbar_->setValue(0);
+  }
+}
+
 void ViewerSizer::HandDragMove(int x, int y)
 {
   if (horiz_scrollbar_->isVisible()) {
@@ -104,28 +133,9 @@ bool ViewerSizer::eventFilter(QObject *watched, QEvent *event)
       QWheelEvent *w = static_cast<QWheelEvent*>(event);
 
       if (HandMovableView::WheelEventIsAZoomEvent(w)) {
-        int current_percent = zoom_;
-        if (current_percent == 0) {
-          // Currently set to "fit"
-          current_percent = current_widget_scale_;
-        }
-
-        double cur_scale = current_percent * 0.01;
-
-        current_percent *= HandMovableView::GetScrollZoomMultiplier(w);
-        current_percent = std::clamp(current_percent, kZoomLevels[0], kZoomLevels[kZoomLevelCount-1]);
-
-        double next_scale = current_percent * 0.01;
-
+        double next_scale = GetRealCurrentZoom() * HandMovableView::GetScrollZoomMultiplier(w);
         QPointF cursor_pos = w->position();
-
-        int anchor_x = qRound(double(cursor_pos.x() + horiz_scrollbar_->value()) / cur_scale * next_scale - cursor_pos.x());
-        int anchor_y = qRound(double(cursor_pos.y() + vert_scrollbar_->value()) / cur_scale * next_scale - cursor_pos.y());
-
-        SetZoom(current_percent);
-
-        horiz_scrollbar_->setValue(anchor_x);
-        vert_scrollbar_->setValue(anchor_y);
+        SetZoomAnchored(next_scale, cursor_pos.x(), cursor_pos.y());
       } else {
         // Pass scroll values to scrollbars
         QPoint p = w->pixelDelta();
@@ -218,12 +228,12 @@ void ViewerSizer::UpdateSize()
 
   }
 
-  current_widget_scale_ = current_scale * 100;
+  current_widget_scale_ = current_scale;
 
   if (zoom_ > 0) {
 
     // Scale to get to the requested zoom
-    double zoom_diff = (zoom_ * 0.01) / current_scale;
+    double zoom_diff = zoom_ / current_scale;
     child_matrix.scale(zoom_diff, zoom_diff, 1.0);
 
   }
@@ -235,7 +245,18 @@ void ViewerSizer::UpdateSize()
 
 int ViewerSizer::GetZoomedValue(int value)
 {
-  return qRound(value * static_cast<double>(zoom_) * 0.01);
+  return qRound(value * zoom_);
+}
+
+double ViewerSizer::GetRealCurrentZoom() const
+{
+  if (zoom_ < 0) {
+    // Currently set to "fit"
+    return current_widget_scale_;
+  } else {
+    // Explicit zoom set
+    return zoom_;
+  }
 }
 
 void ViewerSizer::ScrollBarMoved()

app/widget/viewer/viewersizer.h

@@ -51,8 +51,10 @@ public:
    */
   void SetWidget(QWidget* widget);
 
-  static constexpr int kZoomLevelCount = 8;
-  static constexpr int kZoomLevels[kZoomLevelCount] = {10, 25, 50, 75, 100, 150, 200, 400};
+  QSize GetContainerSize() const;
+
+  static constexpr int kZoomLevelCount = 10;
+  static constexpr double kZoomLevels[kZoomLevelCount] = {0.05, 0.1, 0.25, 0.5, 0.75, 1.0, 1.5, 2.0, 4.0, 8.0};
 
 public slots:
   /**
@@ -72,7 +74,8 @@ public slots:
    *
    * The number is an integer percentage (100 = 100%). Set to 0 to auto-fit.
    */
-  void SetZoom(int percent);
+  void SetZoom(double percent);
+  void SetZoomAnchored(double percent, double cursor_x, double cursor_y);
 
   void HandDragMove(int x, int y);
 
@@ -97,6 +100,8 @@ private:
 
   int GetZoomedValue(int value);
 
+  double GetRealCurrentZoom() const;
+
   /**
    * @brief Reference to widget
    *
@@ -115,8 +120,8 @@ private:
   /**
    * @brief Internal zoom value
    */
-  int zoom_;
-  int current_widget_scale_;
+  double zoom_;
+  double current_widget_scale_;
 
   QScrollBar* horiz_scrollbar_;
   QScrollBar* vert_scrollbar_;