QuickShow: When zooming with the mouse wheel, keep image centered at cursor.

1 files changed, 7 insertions, 0 deletions

diff --git a/Applications/QuickShow/QSWidget.cpp b/Applications/QuickShow/QSWidget.cpp
index 1aa667d03b..a7cda20ef8 100644
--- a/Applications/QuickShow/QSWidget.cpp
+++ b/Applications/QuickShow/QSWidget.cpp
@@ -72,12 +72,19 @@ void QSWidget::mousemove_event(GMouseEvent& event)
 void QSWidget::mousewheel_event(GMouseEvent& event)
 {
     auto old_scale = m_scale;
+    auto old_scale_factor = (float)m_scale / 100.0f;
+    auto zoom_point = event.position().translated(-m_bitmap_rect.location());
+    zoom_point.set_x((float)zoom_point.x() / old_scale_factor);
+    zoom_point.set_y((float)zoom_point.y() / old_scale_factor);
     m_scale += -event.wheel_delta() * 10;
     if (m_scale < 10)
         m_scale = 10;
     if (m_scale > 1000)
         m_scale = 1000;
     relayout();
+    auto new_scale_factor = (float)m_scale / 100.0f;
+    auto scale_factor_change = new_scale_factor - old_scale_factor;
+    m_bitmap_rect.move_by(-Point((float)zoom_point.x() * scale_factor_change, (float)zoom_point.y() * scale_factor_change));
     if (old_scale != m_scale) {
         if (on_scale_change)
             on_scale_change(m_scale);