From c696c85dd4e93c8523bfb868dd4f668b97e964f0 Mon Sep 17 00:00:00 2001
From: Carl Simonson <simonsonc@gmail.com>
Date: Thu, 31 May 2012 18:16:19 -0500
Subject: [PATCH] viewer: add mouse wheel zooming

This change makes the viewer zoom in and out when using the scroll wheel.
The zoom tracks the position of the mouse pointer when zooming in so that
the map will be centered under the mouse after a zoom.
---
 demo/viewer/mapwidget.cpp | 26 ++++++++++++++++++++++++++
 demo/viewer/mapwidget.hpp |  1 +
 2 files changed, 27 insertions(+)

diff --git a/demo/viewer/mapwidget.cpp b/demo/viewer/mapwidget.cpp
index 8717cf4a8..102dfe030 100644
--- a/demo/viewer/mapwidget.cpp
+++ b/demo/viewer/mapwidget.cpp
@@ -289,6 +289,32 @@ void MapWidget::mouseReleaseEvent(QMouseEvent* e)
    }
 }
 
+void MapWidget::wheelEvent(QWheelEvent* e)
+{
+   if (!map_)
+   {
+      return;
+   }
+
+   QPoint corner(map_->width(), map_->height());
+   QPoint zoomCoords;
+   double zoom;
+   if (e->delta() > 0)
+   {
+      zoom = 0.5;
+      QPoint center = corner / 2;
+      QPoint delta = e->pos() - center;
+      zoomCoords = zoom * delta + center;
+   }
+   else
+   {
+      zoom = 2.0;
+      zoomCoords = corner - e->pos();
+   }
+
+   map_->pan_and_zoom(zoomCoords.x(), zoomCoords.y(), zoom);
+   updateMap();
+}
 
 void MapWidget::keyPressEvent(QKeyEvent *e)
 {
diff --git a/demo/viewer/mapwidget.hpp b/demo/viewer/mapwidget.hpp
index e440ce2c2..671cc5ab4 100644
--- a/demo/viewer/mapwidget.hpp
+++ b/demo/viewer/mapwidget.hpp
@@ -99,6 +99,7 @@ protected:
     void mousePressEvent(QMouseEvent* e);
     void mouseMoveEvent(QMouseEvent* e);
     void mouseReleaseEvent(QMouseEvent* e);
+    void wheelEvent(QWheelEvent* e);
     void keyPressEvent(QKeyEvent *e);
     void export_to_file(unsigned width,
                         unsigned height,