[Interest] [Qt 5, OS X] Does OpenGL 3 Core Profile work (with Qt APIs)?

[Samuel Rødal]

On 04/22/2013 10:40 AM, Till Oliver Knoll wrote:
> 2013/4/20 James Turner <james.turner at kdab.com>:
>>
>> On 18 Apr 2013, at 09:09, Till Oliver Knoll <till.oliver.knoll at gmail.com>
>> wrote:
>>
>> So is OpenGL 3.x Core actually supposed to work with Qt 5? Or is this
>> still work in progress?
>>
>>
>> It works fine, but the legacy QGL APIs don't help you much. Rough
>> pseudo-code which works for me:
>>
>>     QWindow *win = new QWindow
>>      win->setSurfaceType( OpenGLSurface );
>>
>>      QSurfaceFormat format;
>>      format.setMajorVersion( 3 );
>>      format.setMinorVersion( 2 );
>>      format.setProfile( QSurfaceFormat::CoreProfile );
>
> Thanks for the hint about QWindow/OpenGLSurface - didn't know that new
> Qt 5 API yet ;)

Sean did a nice write-up on what's happening on the OpenGL side in Qt 5: 
http://www.kdab.com/opengl-in-qt-5-1-part-1

> And I figured out by now why the previously mentioned "OpenGL Windows"
> example "did not work":
>
>    http://qt-project.org/doc/qt-5.0/qtgui/openglwindow.html
>
> It uses the said QWindow API and basically re-implements the QGLWidget
> "initialise-/paint-/resizeGL" functionality - without actually
> rendering anything, hence my impression that "it did not work".

> I yet have to try out that "TriangleWindow" example code and see
> whether it actually works.

examples/opengl/hellowindow is also QWindow-based. Also, any QtQuick 2.0 
application will use QWindow and QOpenGLContext and no QWidget or 
QGL*-classes.

> However, even it it would work and apart from the huge performance
> issues: it would be of no use to me, because QWindow is not derived
> from QWidget, is it? So what's the use of having a GL based windows in
> a *desktop* application (except for "full-screen" usage maybe)? I
> really need a QGLWidget...

In 5.1 you can use QWidget::createWindowContainer() to embed a QWindow 
in a QWidget-hierarchy. But yes, we should probably have a QOpenGLWidget 
to replace QGLWidget at some point (so that the QtOpenGL module can be 
fully deprecated).

> And apart from QGLWidget and QGLFormat - which apparenty are /not/
> deprecated in Qt 5, and I don't see any QOpenGLFormat, for instance -
> I am not using any deprecated Qt OpenGL functionality AFAICT: I
> replaced the QGLShaderProgram with QOpenGLShaderProgram.

QSurfaceFormat is meant to be the replacement for QGLFormat.

> My assumption/expectation is off course that QOpenGLShaderProgram
> /should/ work within a QGLWidget - with a Core 3.2 GL context, that
> is.
>
> I'll investigate more, especially I will start over from an example
> that actually /does/ work from the very beginning, and try to squeeze
> that into a QGLWidget with a Core 3.2 GL context, using QOpenGLShader.

Hmm yes, I don't see why QOpenGLShaderProgram shouldn't work with a 
QGLWidget. Internally QGLWidget (well QWidget really) and QGLContext are 
implemented on top of QWindow and QOpenGLContext now (in qwidget_qpa.cpp 
and qgl_qpa.cpp respectively).

--
Samuel