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A sample highlighting QGraphicsEffect
Introduction
While learning Qt, I wrote this sample highlighting graphics effect to be used with rectangular QGraphicsPixmapItem... and I use this post just to learn how to publish a wiki page here too.. ;-)
highlight.h
#ifndef HIGHLIGHT_H
#define HIGHLIGHT_H
#include <QtGui>
class HighlightEffect : public QGraphicsEffect
{
Q_OBJECT
Q_PROPERTY( QColor color READ color WRITE setColor )
Q_PROPERTY( QPointF offset READ offset WRITE setOffset )
public:
HighlightEffect( qreal offset = 1.5 );
virtual QRectF boundingRectFor( const QRectF& sourceRect; ) const;
QColor color() const { return mColor;}
void setColor( QColor& color; ) { mColor = color;}
QPointF offset() const { return mOffset;}
void setOffset( QPointF offset ) { mOffset = offset;}
protected:
virtual void draw( QPainter *painter ); // , QGraphicsEffectSource *source );
private:
QColor mColor;
QPointF mOffset;
};
#endif // HIGHLIGHT_H
highlight.cpp
#include "highlight.h"
HighlightEffect::HighlightEffect( qreal offset ) :
QGraphicsEffect(),
mColor( 255, 255, 0, 128 ), // yellow, semi-transparent
mOffset( offset, offset ) {}
QRectF HighlightEffect::boundingRectFor( const QRectF& sourceRect; ) const
{
return sourceRect.adjusted( -mOffset.x(), -mOffset.y(), mOffset.x(), mOffset.y() );
}
void HighlightEffect::draw( QPainter* painter )
{
QPoint offset;
QPixmap pixmap;
// if ( sourceIsPixmap() ) // doesn't seems to work, return false
// {
// No point in drawing in device coordinates (pixmap will be scaled anyways).
pixmap = sourcePixmap( Qt::LogicalCoordinates, &offset; );
//}
QRectF bound = boundingRectFor( pixmap.rect() );
painter->save();
painter->setPen( Qt::NoPen );
painter->setBrush( mColor );
QPointF p( offset.x()-mOffset.x(), offset.y()-mOffset.y() );
bound.moveTopLeft( p );
painter->drawRoundedRect( bound, 5, 5, Qt::RelativeSize );
painter->drawPixmap( offset, pixmap );
painter->restore();
}
The strange thing in the implementation is that the sourceIsPixmap function returns always false, even if the documentation states that Returns true if the source effectively is a pixmap, e.g., a QGraphicsPixmapItem. I asked the Qt gurus what can be going on here...
The default color is pale yellow, semi-transparent and the border size is set to 1.5. To add the effect simply add this:
Pixmap *item = new Pixmap(kineticPix);
.
.
HighlightEffect *effect = new HighlightEffect();
item->setGraphicsEffect( effect );
Here the modified animated tiles example with the effect turned on:
Animated tiles example with QGraphicsPixmapItem highlighting
Hope someone finds this useful.