diff --git a/ci-scripts/osx/travis-build.sh b/ci-scripts/osx/travis-build.sh
index a8671414..cbe2a231 100644
--- a/ci-scripts/osx/travis-build.sh
+++ b/ci-scripts/osx/travis-build.sh
@@ -4,7 +4,7 @@ pushd thirdparty/tiff-4.0.3
 popd
 cd toonz && mkdir build && cd build
 cmake ../sources \
-      -DQT_PATH=/usr/local/Cellar/qt5/5.6.1-1/lib/ \
+      -DQT_PATH=/usr/local/Cellar/qt@5.5/5.5.1_1/lib/ \
       -DTIFF_INCLUDE_DIR=../../thirdparty/tiff-4.0.3/libtiff/ \
       -DSUPERLU_INCLUDE_DIR=../../thirdparty/superlu/SuperLU_4.1/include/
 make
diff --git a/ci-scripts/osx/travis-install.sh b/ci-scripts/osx/travis-install.sh
index 1d99806d..5a2358d1 100644
--- a/ci-scripts/osx/travis-install.sh
+++ b/ci-scripts/osx/travis-install.sh
@@ -1,8 +1,5 @@
 #!/bin/bash
 brew update
-brew install glew lz4 lzo libusb
+brew install qt55 glew lz4 lzo libusb
 brew tap tcr/tcr
 brew install clang-format
-# revert to the previous version of the formula to get qt5.6.1-1
-curl -O https://raw.githubusercontent.com/Homebrew/homebrew-core/fdfc724dd532345f5c6cdf47dc43e99654e6a5fd/Formula/qt5.rb
-brew install ./qt5.rb
diff --git a/toonz/sources/include/toonzqt/glwidget_for_highdpi.h b/toonz/sources/include/toonzqt/glwidget_for_highdpi.h
index c81533af..2bae136c 100644
--- a/toonz/sources/include/toonzqt/glwidget_for_highdpi.h
+++ b/toonz/sources/include/toonzqt/glwidget_for_highdpi.h
@@ -16,6 +16,9 @@ public:
                      Qt::WindowFlags f            = Qt::WindowFlags())
       : QGLWidget(parent, shareWidget, f) {}
 
+  // returns device-pixel ratio. It is 1 for normal monitors and 2 (or higher
+  // ratio) for high DPI monitors. Setting "Display > Set custom text size(DPI)"
+  // for Windows corresponds to this ratio.
   int getDevPixRatio() const {
     static int devPixRatio = QApplication::desktop()->devicePixelRatio();
     return devPixRatio;
diff --git a/toonz/sources/toonz/subcameramanager.cpp b/toonz/sources/toonz/subcameramanager.cpp
index 5332188d..0b53d453 100644
--- a/toonz/sources/toonz/subcameramanager.cpp
+++ b/toonz/sources/toonz/subcameramanager.cpp
@@ -119,7 +119,7 @@ bool PreviewSubCameraManager::mousePressEvent(SceneViewer *viewer,
   if (viewer->is3DView()) return true;
 
   m_mousePressed  = true;
-  m_mousePressPos = event->pos() * TApp::instance()->getDevPixRatio();
+  m_mousePressPos = event->pos() * viewer->getDevPixRatio();
   m_dragType      = getSubCameraDragEnum(viewer, m_mousePressPos);
 
   if (bitwiseExclude(m_dragType, OUTER))
@@ -133,7 +133,7 @@ bool PreviewSubCameraManager::mousePressEvent(SceneViewer *viewer,
 bool PreviewSubCameraManager::mouseMoveEvent(SceneViewer *viewer,
                                              QMouseEvent *event) {
   if (viewer->is3DView()) return true;
-  QPoint curPos(event->pos() * TApp::instance()->getDevPixRatio());
+  QPoint curPos(event->pos() * viewer->getDevPixRatio());
   if (event->buttons() == Qt::LeftButton) {
     if (!bitwiseContains(m_dragType, INNER)) {
       if (abs(curPos.x() - m_mousePressPos.x()) > 10 ||
diff --git a/toonz/sources/toonz/tapp.cpp b/toonz/sources/toonz/tapp.cpp
index 61269aa6..5988f2c9 100644
--- a/toonz/sources/toonz/tapp.cpp
+++ b/toonz/sources/toonz/tapp.cpp
@@ -739,10 +739,3 @@ QString TApp::getCurrentRoomName() const {
 
   return currentRoom->getName();
 }
-
-//-----------------------------------------------------------------------------
-
-int TApp::getDevPixRatio() const {
-  static int devPixRatio = QApplication::desktop()->devicePixelRatio();
-  return devPixRatio;
-}
\ No newline at end of file
diff --git a/toonz/sources/toonz/tapp.h b/toonz/sources/toonz/tapp.h
index 96e356d6..e057482f 100644
--- a/toonz/sources/toonz/tapp.h
+++ b/toonz/sources/toonz/tapp.h
@@ -201,11 +201,6 @@ public:
 
   void writeSettings();
 
-  // returns device-pixel ratio. It is 1 for normal monitors and 2 (or higher
-  // ratio) for high DPI monitors. Setting "Display > Set custom text size(DPI)"
-  // for Windows corresponds to this ratio.
-  int getDevPixRatio() const;
-
 protected:
   bool eventFilter(QObject *obj, QEvent *event) override;