update() & updateGL()

[rick_st3]

hi.
What I wanted to know was, is there any difference between update() and updateGL()..? i mean i tried calling both of them in my code,and both of them were executing the paintGL() function...

[wysota]

I think update() for QGLWidget is calling updateGL() (or the other way round), so you can use either of them.

[rick_st3]

soo... if u can call a QGLWidget with a simple update() then what's the point in having an updateGL()...??

[wysota]

void QGLWidget::updateGL()
{
    if (updatesEnabled())
        glDraw();
}

void QGLWidget::updateGL()
{
    if (updatesEnabled())
        glDraw();
}

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void QGLWidget::paintEvent(QPaintEvent *)
{
    if (updatesEnabled()) {
        glDraw();
        updateOverlayGL();
    }
}

void QGLWidget::paintEvent(QPaintEvent *)
{
    if (updatesEnabled()) {
        glDraw();
        updateOverlayGL();
    }
}

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Do you see the difference?

[spud]

updateGL() should be at least as fast, if not faster than update() since it bypasses the QWidget paint system with clipping, region updating and what have you.

A quick dump of the call stack (on windows) shows that update() has the following calling order:

>	gltest.exe!GLWidget::paintGL()  Line 18	C++
 	QtOpenGLd4.dll!QGLWidget::glDraw()  Line 3111	C++
 	QtOpenGLd4.dll!QGLWidget::paintEvent(QPaintEvent * __formal=0x0012c354)  Line 2898	C++
...
 	QtGuid4.dll!QWidgetPrivate::drawWidget(QPaintDevice * pdev=0x0012feb8, const QRegion & rgn={...}, const QPoint & offset={...}, int flags=3)  Line 1212 + 0xd bytes	C++
 	QtGuid4.dll!QWidget::repaint(const QRegion & rgn={...})  Line 1310	C++
 	QtGuid4.dll!qt_syncBackingStore(QRegion rgn={...}, QWidget * widget=0x0012feb0, bool recursive=true)  Line 250	C++
 	QtGuid4.dll!QETWidget::translatePaintEvent(const tagMSG & msg={...})  Line 3111 + 0x2b bytes	C++
...

>	gltest.exe!GLWidget::paintGL()  Line 18	C++
 	QtOpenGLd4.dll!QGLWidget::glDraw()  Line 3111	C++
 	QtOpenGLd4.dll!QGLWidget::paintEvent(QPaintEvent * __formal=0x0012c354)  Line 2898	C++
...
 	QtGuid4.dll!QWidgetPrivate::drawWidget(QPaintDevice * pdev=0x0012feb8, const QRegion & rgn={...}, const QPoint & offset={...}, int flags=3)  Line 1212 + 0xd bytes	C++
 	QtGuid4.dll!QWidget::repaint(const QRegion & rgn={...})  Line 1310	C++
 	QtGuid4.dll!qt_syncBackingStore(QRegion rgn={...}, QWidget * widget=0x0012feb0, bool recursive=true)  Line 250	C++
 	QtGuid4.dll!QETWidget::translatePaintEvent(const tagMSG & msg={...})  Line 3111 + 0x2b bytes	C++
...

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whereas updateGL() gets down to business faster:

>	gltest.exe!GLWidget::paintGL()  Line 18	C++
 	QtOpenGLd4.dll!QGLWidget::glDraw()  Line 3111	C++
 	QtOpenGLd4.dll!QGLWidget::updateGL()  Line 2768	C++

>	gltest.exe!GLWidget::paintGL()  Line 18	C++
 	QtOpenGLd4.dll!QGLWidget::glDraw()  Line 3111	C++
 	QtOpenGLd4.dll!QGLWidget::updateGL()  Line 2768	C++

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(I left out the Signal/Slot messaging calls in both examples)

[rick_st3]

@ wysota
errrr....no.... i can see an updateGL() function but no update()...!!

@ spud

the code didn't make that much sense to me but i think i got what it basically meant...!! thanks...

[wysota]

@ wysota
errrr....no.... i can see an updateGL() function but no update()...!!

update() schedules a paintEvent.

[rick_st3]

oh..!! had completely forgotten it...!! anyways thanx mate...!!