viewerwindow: implemented displaying a viewer image fullscreen on another monitor

Implements an extra widget to display images on a separate monitor. Both
viewers have separate display color controls since different monitors may
conform to different standards/transforms.

app/widget/viewer/viewerwindow.cpp

@@ -0,0 +1,55 @@
+#include "viewerwindow.h"
+
+#include <QKeyEvent>
+#include <QVBoxLayout>
+
+ViewerWindow::ViewerWindow(QWidget *parent) :
+  QWidget(parent, Qt::Window | Qt::WindowStaysOnTopHint)
+{
+  QVBoxLayout* layout = new QVBoxLayout(this);
+  layout->setMargin(0);
+  layout->setSpacing(0);
+
+  gl_widget_ = new ViewerGLWidget();
+  layout->addWidget(gl_widget_);
+}
+
+ViewerGLWidget *ViewerWindow::gl_widget() const
+{
+  return gl_widget_;
+}
+
+void ViewerWindow::SetResolution(int width, int height)
+{
+  // Set GL widget matrix to maintain this texture's aspect ratio
+  double window_ar = static_cast<double>(this->width()) / static_cast<double>(this->height());
+  double image_ar = static_cast<double>(width) / static_cast<double>(height);
+
+  QMatrix4x4 mat;
+
+  if (window_ar > image_ar) {
+    // Window is wider than image, adjust X scale
+    mat.scale(image_ar / window_ar, 1.0f, 1.0f);
+  } else if (window_ar < image_ar) {
+    // Window is taller than image, adjust Y scale
+    mat.scale(1.0f, window_ar / image_ar, 1.0f);
+  }
+
+  gl_widget_->SetMatrix(mat);
+}
+
+void ViewerWindow::keyPressEvent(QKeyEvent *e)
+{
+  QWidget::keyPressEvent(e);
+
+  if (e->key() == Qt::Key_Escape) {
+    close();
+  }
+}
+
+void ViewerWindow::closeEvent(QCloseEvent *e)
+{
+  QWidget::closeEvent(e);
+
+  deleteLater();
+}