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qt'QColorLuminancePicker (./qt-2.1.0/src/dialogs/qcolordialog.cpp:256)

class QColorLuminancePicker : public QWidget
{
    Q_OBJECT
public:
    QColorLuminancePicker(QWidget* parent=0, const char* name=0);
    ~QColorLuminancePicker();

public slots:
    void setCol( int h, int s, int v );
    void setCol( int h, int s );

signals:
    void newHsv( int h, int s, int v );

protected:
//    QSize sizeHint() const;
//    QSizePolicy sizePolicy() const;
    void paintEvent( QPaintEvent*);
    void mouseMoveEvent( QMouseEvent * );
    void mousePressEvent( QMouseEvent * );

private:
    enum { foff = 3, coff = 4 }; //frame and contents offset
    int val;
    int hue;
    int sat;

    int y2val( int y );
    int val2y( int val );
    void setVal( int v );

    QPixmap *pix;
};


int QColorLuminancePicker::y2val( int y )
{
    int d = height() - 2*coff - 1;
    return 255 - (y - coff)*255/d;
}

int QColorLuminancePicker::val2y( int v )
{
    int d = height() - 2*coff - 1;
    return coff + (255-v)*d/255;
}

QColorLuminancePicker::QColorLuminancePicker(QWidget* parent,
						  const char* name)
    :QWidget( parent, name )
{
    hue = 100; val = 100; sat = 100;
    pix = 0;
    //    setBackgroundMode( NoBackground );
}

QColorLuminancePicker::~QColorLuminancePicker()
{
    delete pix;
}

void QColorLuminancePicker::mouseMoveEvent( QMouseEvent *m )
{
    setVal( y2val(m->y()) );
}
void QColorLuminancePicker::mousePressEvent( QMouseEvent *m )
{
    setVal( y2val(m->y()) );
}

void QColorLuminancePicker::setVal( int v )
{
    if ( val == v )
	return;
    val = QMAX( 0, QMIN(v,255));
    delete pix; pix=0;
    repaint( FALSE ); //###
    emit newHsv( hue, sat, val );
}

//receives from a hue,sat chooser and relays.
void QColorLuminancePicker::setCol( int h, int s )
{
    setCol( h, s, val );
    emit newHsv( h, s, val );
}

void QColorLuminancePicker::paintEvent( QPaintEvent * )
{
    int w = width() - 5;

    QRect r( 0, foff, w, height() - 2*foff );
    int wi = r.width() - 2;
    int hi = r.height() - 2;
    if ( !pix || pix->height() != hi || pix->width() != wi ) {
	delete pix;
	QImage img( wi, hi, 32 );
	int y;
	for ( y = 0; y < hi; y++ ) {
	    QColor c( hue, sat, y2val(y+coff), QColor::Hsv );
	    QRgb r = c.rgb();
	    int x;
	    for ( x = 0; x < wi; x++ )
		img.setPixel( x, y, r );
	}
	pix = new QPixmap;
	pix->convertFromImage(img);
    }
    QPainter p(this);
    p.drawPixmap( 1, coff, *pix );
    QColorGroup g = colorGroup();
    qDrawShadePanel( &p, r, g, TRUE );
    p.setPen( g.foreground() );
    p.setBrush( g.foreground() );
    QPointArray a;
    int y = val2y(val);
    a.setPoints( 3, w, y, w+5, y+5, w+5, y-5 );
    erase( w, 0, 5, height() );
    p.drawPolygon( a );
}

void QColorLuminancePicker::setCol( int h, int s , int v )
{
    val = v;
    hue = h;
    sat = s;
    delete pix; pix=0;
    repaint( FALSE );//####
}

qt'QColorLuminancePicker::setCol() (./qt-2.1.0/src/dialogs/qcolordialog.cpp:377)

void QColorLuminancePicker::setCol( int h, int s , int v )
{
    val = v;
    hue = h;
    sat = s;
    delete pix; pix=0;
    repaint( FALSE );//####
}