QVTKOpenGLWidget: Set screen size on render window

QVTKOpenGLWidget requires using vtkGenericOpenGLRenderWindow. The
vtkWindow interface requires implementing GetScreenSize() to return the
size of the screen in pixels.

This commit makes QVTKOpenGLWidget responsible for determining the
size of its screen and setting that size on its
vtkGenericOpenGLRenderWindow.

GUISupport/Qt/QVTKOpenGLWidget.cxx

@@ -14,6 +14,8 @@
 =========================================================================*/
 #include "QVTKOpenGLWidget.h"
 
+#include <QApplication>
+#include <QDesktopWidget>
 #include <QMouseEvent>
 #include <QOpenGLContext>
 #include <QOpenGLDebugLogger>
@@ -339,6 +341,10 @@ void QVTKOpenGLWidget::recreateFBO()
   this->RenderWindow->SetSize(deviceSize.width(), deviceSize.height());
   this->RenderWindow->SetPosition(this->x() * devicePixelRatio_, this->y() * devicePixelRatio_);
 
+  // Set screen size on render window.
+  const QRect screenGeometry = QApplication::desktop()->screenGeometry(this);
+  this->RenderWindow->SetScreenSize(screenGeometry.width(), screenGeometry.height());
+
   this->FBO = new QOpenGLFramebufferObject(deviceSize, format);
   this->FBO->bind();
   this->RenderWindow->SetForceMaximumHardwareLineWidth(1);

GUISupport/Qt/Testing/Cxx/TestQVTKOpenGLWidget.cxx

@@ -62,6 +62,16 @@ int TestQVTKOpenGLWidget(int argc, char* argv[])
   actor->SetMapper(mapper.Get());
   ren->AddActor(actor.Get());
 
+  int* windowSize = window->GetSize();
+  int* screenSize = window->GetScreenSize();
+  if (screenSize[0] < windowSize[0] || screenSize[1] < windowSize[1])
+  {
+    std::cout << "Expected vtkGenericOpenGLRenderWindow::GetScreenSize() "
+      "dimensions to be larger than the render window size"
+      << std::endl;
+    return EXIT_FAILURE;
+  }
+
   vtktesting->SetRenderWindow(window.Get());
   widget.update();
   app.processEvents();

Rendering/OpenGL2/vtkGenericOpenGLRenderWindow.cxx

@@ -30,6 +30,8 @@ vtkGenericOpenGLRenderWindow::vtkGenericOpenGLRenderWindow()
   this->CurrentStatus = false;
   this->SupportsOpenGLStatus = 0;
   this->ForceMaximumHardwareLineWidth = 0;
+  this->ScreenSize[0] = 0;
+  this->ScreenSize[1] = 0;
 }
 
 vtkGenericOpenGLRenderWindow::~vtkGenericOpenGLRenderWindow()
@@ -170,7 +172,7 @@ void vtkGenericOpenGLRenderWindow::SetParentInfo(char*)
 
 int* vtkGenericOpenGLRenderWindow::GetScreenSize()
 {
-  return nullptr;
+  return this->ScreenSize;
 }
 
 void vtkGenericOpenGLRenderWindow::Start()

Rendering/OpenGL2/vtkGenericOpenGLRenderWindow.h

@@ -151,12 +151,18 @@ class VTKRENDERINGOPENGL2_EXPORT vtkGenericOpenGLRenderWindow :
   vtkSetMacro(ReadyForRendering, bool);
   vtkGetMacro(ReadyForRendering, bool);
 
+  /**
+   * Set the size of the screen in pixels.
+   */
+  vtkSetVector2Macro(ScreenSize,int);
+
 protected:
   int DirectStatus;
   int SupportsOpenGLStatus;
   bool CurrentStatus;
   float ForceMaximumHardwareLineWidth;
   bool ReadyForRendering;
+  int ScreenSize[2];
 
 private:
   vtkGenericOpenGLRenderWindow(const vtkGenericOpenGLRenderWindow&) VTK_DELETE_FUNCTION;