No, that is expected. After all it has to look up the versionFunction internals
from the hash table maintained by the context.
With the design shown here, deriving GL_Model from QOpenGLFunctions* feels like
an overkill indeed.
The options I see are:
1. Do not derive, just get an QOpenGLFunctions* instance. This of course leads
to the f->glBlah() type of code which some (myself not included) may find ugly.
2. Use a different design. Separating the GL initialization/rendering into a
separate class (e.g. GL_ModelRenderer) with a single instance could avoid the
issue altogether.
Cheers,
Laszlo
________________________________________
From: interest-bounces+laszlo.agocs=digia....@qt-project.org
[interest-bounces+laszlo.agocs=digia....@qt-project.org] on behalf of Yves
Bailly [yves.bai...@sescoi.fr]
Sent: Monday, March 17, 2014 12:38 PM
To: interest@qt-project.org
Subject: Re: [Interest] Using OpenGL with Qt
Le 17/03/2014 10:05, Agocs Laszlo a écrit :
> I must correct my previous statement about not resolving functions that are
> not called. This deferred behavior is only true for QOpenGLFunctions. The
> versioned variants will resolve all functions for the given version already
> when initializeOpenGLFunctions() is first called with a given context.
Here's what I tried.
First I define a default GL format:
QGLFormat fmt;
fmt.setVersion(3, 3);
fmt.setProfile(QGLFormat::CoreProfile);
fmt.setStencilBufferSize(8);
QGLFormat::setDefaultFormat(fmt);
Now let's say I have two classes:
class Gl_Model: protected QOpenGLFunctions_3_3_Core
{
public:
Gl_Model();
void create();
void draw();
private:
GLuint buff_ids[3];
}; // class Gl_Model
class Gl_Widget:
public QGLWidget,
protected QOpenGLFunctions_3_3_Core
{
Q_OBJECT
public:
explicit Gl_Widget(QWidget* const parent = nullptr);
protected:
virtual void initializeGL() override;
virtual void paintGL() override;
virtual void resizeGL(int width, int height) override;
private:
Gl_Model* model{nullptr};
}; // class Gl_Widget
inside Gl_Model::create():
void Gl_Model::create()
{
this->initializeOpenGLFunctions();
/* ... */
}
inside Gl_Widget::initializeGL():
{
QOpenGLContext* ctx = QOpenGLContext::currentContext();
ctx->versionFunctions<QOpenGLFunctions_3_3_Core>();
this->initializeOpenGLFunctions();
this->model = new Gl_Model;
this->model->create();
}
Now if I follow the program step-by-step, indeed the second call to
initializeOpenGLFunctions (inside Gl_Model::create) it will reuse some
already allocated data... but it will perform 12 searchs in a QHash<>.
If I have to create, say, 100000 instances of Gl_Model, that will
imply 1200000 searchs. I know QHash<> is quite fast, but that seems
a bit overkill to me...
Or am I missing something again?
--
/- Yves Bailly - Software developer -\
\- Sescoi R&D - http://www.sescoi.fr -/
"The possible is done. The impossible is being done. For miracles,
thanks to allow a little delay."
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