flashing widgets

[tksharpless]

I need a bunch of controls that have fixed signal/slot bindings but can be placed into various dialogs depending on app modes. My solution is a widget that creates the control widgets as children of itself, but does not show them; it then connects to their signals using QMetaObject::connectSlotsByName(). Later I insert the controls into layouts in the variable dialogs.

This works nicely except for one glitch: the control widgets "flash" briefly on screen as they are being created (on WinVista32, haven't tried others). The "flash" is not the whole widget, just a small window frame, -- whose style changes according to window flags passed to the widget c'tor. It happens whether the generating widget has a parent or not ( I create it parentless, otherwise a permanent small black rectangle shows in the parent's client area).

Can anyone suggest a solution?

Thanks, Tom

[marcvanriet]

I suppose you do setVisible( false ) after you create the widget but before you add it to the control widget ?

regards,
Marc

[tksharpless]

Hi Marc

Yes, I set the widgets invisible at creation and make them visible again before use. The flashing frames show up even if I set all the component widgets invisible too.

-- Tom

[wysota]

Can we see some code?

[tksharpless]

Here is the code that creates the flashing widgets

PaniniParameters::PaniniParameters( QWidget *parent )
   : QWidget(0) // else get black hole in parent window
{
    ppar = parent;
    genCtl( "upPitch", "pitch", -90, 90, 0,
            tr("pitch to world vertical, degrees"), QString());
    genCtl( "upRoll", "roll", -90, 90, 0,
            tr("roll to world vertical, degrees"), QString());
    genCtl( "camZoom", "zoom", 0, 100, 0,
            tr("lens zoom, % of range"),
            QString("photo"));
 
... <10 more like those> ...
 
  // connect signals to our slots
    QMetaObject::connectSlotsByName( this );
}
 
void PaniniParameters::genCtl( const QString &name,
                               const QString &label,
                               double lo, double hi, double def,
                               const QString &tip,
                               const QString &chkLbl )
{
    PaniniSlide * ps = new PaniniSlide( this, label, lo, hi, def, tip, chkLbl );
    ps->setObjectName( name );
    names_addrs.insert( name, ps );
}

PaniniParameters::PaniniParameters( QWidget *parent )
   : QWidget(0) // else get black hole in parent window
{
    ppar = parent;
    genCtl( "upPitch", "pitch", -90, 90, 0,
            tr("pitch to world vertical, degrees"), QString());
    genCtl( "upRoll", "roll", -90, 90, 0,
            tr("roll to world vertical, degrees"), QString());
    genCtl( "camZoom", "zoom", 0, 100, 0,
            tr("lens zoom, % of range"),
            QString("photo"));

... <10 more like those> ...
    
  // connect signals to our slots
    QMetaObject::connectSlotsByName( this );
}

void PaniniParameters::genCtl( const QString &name,
                               const QString &label,
                               double lo, double hi, double def,
                               const QString &tip,
                               const QString &chkLbl )
{
    PaniniSlide * ps = new PaniniSlide( this, label, lo, hi, def, tip, chkLbl );
    ps->setObjectName( name );
    names_addrs.insert( name, ps );
}

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Here is the c'tor of PaniniSlide:

PaniniSlide::PaniniSlide( QWidget * parent,
                  const QString & lblv,
                  float lo, float hi,
                  float initv,
                  const QString & tip,
                  const QString & checkText,
                  bool vert,
                  int minlen, int maxlen
                  )
    : QWidget( parent )
{
    if(minlen < 1) minlen = 121;
    if(maxlen < minlen ) maxlen = 1001;
// set checkbox text, hide it if none
    checkbox.setText( checkText );
    checkbox.setVisible( !checkText.isEmpty() );
// set control data
    setLabel( lblv );
    setRange(lo, hi, initv );
 
// set control characteristics
    label.setAlignment(Qt::AlignHCenter);
    spinbox.setButtonSymbols(QAbstractSpinBox::NoButtons);
    slider.setTickInterval(10);
    slider.setTickPosition(QSlider::TicksLeft);
// lay out the controls
    if( vert ) {
        slider.setOrientation ( Qt::Vertical );
        slider.setMinimumHeight( minlen );
        slider.setMaximumHeight( maxlen );
        slider.setSizePolicy( QSizePolicy::Fixed,
                              QSizePolicy::MinimumExpanding );
    } else {
        slider.setOrientation ( Qt::Horizontal );
        slider.setMinimumWidth( minlen );
        slider.setMaximumWidth( maxlen );
        slider.setSizePolicy( QSizePolicy::MinimumExpanding,
                              QSizePolicy::Fixed );
    }
    label.setFixedWidth( minW );
    spinbox.setFixedWidth( minW );
    QBoxLayout::Direction d = vert ? QBoxLayout::TopToBottom
                                   : QBoxLayout::RightToLeft;
    QBoxLayout * lay = new QBoxLayout( d, this );
    lay->addWidget(&slider);
    lay->addWidget(&label);
    lay->addWidget(&spinbox);
    lay->addWidget(&checkbox );
    setLayout( lay );
// minimum widget size
    setMinimumSize( lay->minimumSize() );
    resize( minimumSize() );
// add tool tips
    label.setToolTip( tip );
    spinbox.setToolTip( tip );
    slider.setToolTip(tr("\
 Drag sliders or type numbers.\n\
 Fine adjust: click number and\n\
 use up and down arrow keys.\n\
 Reset: left-dbl-click label.\n\
 Options: right-dbl-click label.\
 "));
 
  //wire signals
    connect( &slider, SIGNAL(valueChanged(int)),
             this, SLOT(on_slider_valueChanged(int)));
    connect( &spinbox, SIGNAL(valueChanged(double)),
             this, SLOT(on_spinbox_valueChanged(double)));
    connect( &checkbox, SIGNAL(stateChanged(int)),
             this, SLOT(on_checkbox_stateChanged(int)));
// enable widget signals
    slider.blockSignals(false);
    spinbox.blockSignals(false);
    checkbox.blockSignals(false);
}

PaniniSlide::PaniniSlide( QWidget * parent,
                  const QString & lblv,
                  float lo, float hi,
                  float initv,
                  const QString & tip,
                  const QString & checkText,
                  bool vert,
                  int minlen, int maxlen
                  )
    : QWidget( parent )
{
    if(minlen < 1) minlen = 121;
    if(maxlen < minlen ) maxlen = 1001;
// set checkbox text, hide it if none
    checkbox.setText( checkText );
    checkbox.setVisible( !checkText.isEmpty() );
// set control data
    setLabel( lblv );
    setRange(lo, hi, initv );

// set control characteristics
    label.setAlignment(Qt::AlignHCenter);
    spinbox.setButtonSymbols(QAbstractSpinBox::NoButtons);
    slider.setTickInterval(10);
    slider.setTickPosition(QSlider::TicksLeft);
// lay out the controls
    if( vert ) {
        slider.setOrientation ( Qt::Vertical );
        slider.setMinimumHeight( minlen );
        slider.setMaximumHeight( maxlen );
        slider.setSizePolicy( QSizePolicy::Fixed,
                              QSizePolicy::MinimumExpanding );
    } else {
        slider.setOrientation ( Qt::Horizontal );
        slider.setMinimumWidth( minlen );
        slider.setMaximumWidth( maxlen );
        slider.setSizePolicy( QSizePolicy::MinimumExpanding,
                              QSizePolicy::Fixed );
    }
    label.setFixedWidth( minW );
    spinbox.setFixedWidth( minW );
    QBoxLayout::Direction d = vert ? QBoxLayout::TopToBottom
                                   : QBoxLayout::RightToLeft;
    QBoxLayout * lay = new QBoxLayout( d, this );
    lay->addWidget(&slider);
    lay->addWidget(&label);
    lay->addWidget(&spinbox);
    lay->addWidget(&checkbox );
    setLayout( lay );
// minimum widget size
    setMinimumSize( lay->minimumSize() );
    resize( minimumSize() );
// add tool tips
    label.setToolTip( tip );
    spinbox.setToolTip( tip );
    slider.setToolTip(tr("\
 Drag sliders or type numbers.\n\
 Fine adjust: click number and\n\
 use up and down arrow keys.\n\
 Reset: left-dbl-click label.\n\
 Options: right-dbl-click label.\
 "));

  //wire signals
    connect( &slider, SIGNAL(valueChanged(int)),
             this, SLOT(on_slider_valueChanged(int)));
    connect( &spinbox, SIGNAL(valueChanged(double)),
             this, SLOT(on_spinbox_valueChanged(double)));
    connect( &checkbox, SIGNAL(stateChanged(int)),
             this, SLOT(on_checkbox_stateChanged(int)));
// enable widget signals
    slider.blockSignals(false);
    spinbox.blockSignals(false);
    checkbox.blockSignals(false);
}

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[wysota]

Could you explain why you don't pass the parent pointer to QWidget constructor? How do you put the PaniniParameters widget in its parent?

[tksharpless]

PaniniParameters does not need a parent because it is never shown, does not emit any signals, and its slots all call global functions. I create it parentless because otherwise it shows as a black rectangle in the upper left corner of its parent (which is a QGLWidget). However, passing its parent pointer to the QWidget c'tor has no effect on the flashing that I can see.

[wysota]

PaniniParameters does not need a parent because it is never shown,

So why is it a widget?

[tksharpless]

That's what I thought. At first I declared : public QObject. But a QWidget c'tor will not accept a QObject * as parent, so it could not create the controls as its children until I made it a QWidget. This is an inconsistency in Qt, since connectSlotsByName() ( as well as signals and slots themselves ) belong to QObject and don't logically need a QWidget. But tha's how it is...

[wysota]

That's what I thought. At first I declared : public QObject. But a QWidget c'tor will not accept a QObject * as parent, so it could not create the controls as its children until I made it a QWidget.

Why should it create the controls as its own children? I think I completely miss the point of what you are doing. I don't even see the reason what you need this extra object for.

[tksharpless]

Why should it create the controls as its own children? I think I completely miss the point of what you are doing. I don't even see the reason what you need this extra object for.

No doubt there are alternatives. But my question was about getting rid of little flashing window frames....