Question

I am migrating some code from FLTK to QT5 and I can’t seem to get a widget in the graphical designed that corresponds to an OpenGL context? Does such a widget exist?

I built QT from the official sources, targeting VS2012x64 with the OpenGL option and have tried to add QT += opengl to my project.pro file.

Answer 1

Qt has the QGLWidget, but you should not use that directly in the Designer. Instead you should place a layout where you want the OpenGL widget to appear. Then you subclass QGLWidget, as you must overwrite the paintGL function anyway to draw something. Then after the setupUI() call you instanciate your custom GL widget and add it to the layout you placed in the designer with layoutinstance->addWidget(…)

update due to comment

mainwindow.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>335</width>
    <height>191</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralwidget">
   <layout class="QVBoxLayout" name="verticalLayout_2">
    <item>
     <layout class="QVBoxLayout" name="verticalLayout"/>
    </item>
   </layout>
  </widget>
  <action name="actionQuit">
   <property name="text">
    <string>&amp;Quit</string>
   </property>
  </action>
 </widget>
 <resources/>
 <connections/>
</ui>

myglwidget.hh

#include <QGLWidget>

class MyGLWidget : public QGLWidget
{ //...
};

mainwindow.hh

#include <QMainWindow>

#include "myglwidget.hh"
#include "mainwindow_ui.hh" // generated by uic

class MainWindow : public QMainWindow, Ui_MainWindow
{

    MainWindow(QObject *parent = NULL) : 
        QMainWindow(parent)
    { // one would implement the constructor in the .cc file of course
        this->setupUi(this);
    
        glwidget = new MyGLWidget(this);

        // using the this pointer to emphase the location of the
        // member variable used.
        // NOTE: In the UI we defined a layout names verticalLayout
        this->verticalLayout->addWidget(glwidget);
    }

protected:
    MyGLWidget *glwidget;
};

The key is, that you use just a layout. An ordinary, regular layout in the UI, to which you add your derived OpenGL widget. No morphs, no promotions in the ui!