QGraphicsPixmapItem zoom out loses percision

[yazwas]

Hello everyone,

I've created an application that uses QGraphicsView & QGraphicsScene, and I've subclassed a QGraphicsPixmapItem,

The application loads an image, around 5 mb of size, it is very fast when it comes to zooming in/out or rotating, but the problem with zooming out is that the image seems to loose precision, and I cant read the lines written anymore


I do the scaling using the following code

qreal imageCenterX = m_imageItem->x()+ m_imageItem->boundingRect().width()/2;
    qreal imageCenterY = m_imageItem->y()+ m_imageItem->boundingRect().height()/2;
 
 
m_imageItem->setTransform(QTransform().translate(imageCenterX, imageCenterY).rotate(angle).scale(zoomFactor, zoomFactor).translate(-imageCenterX, -imageCenterY));

qreal imageCenterX = m_imageItem->x()+ m_imageItem->boundingRect().width()/2;
    qreal imageCenterY = m_imageItem->y()+ m_imageItem->boundingRect().height()/2;


m_imageItem->setTransform(QTransform().translate(imageCenterX, imageCenterY).rotate(angle).scale(zoomFactor, zoomFactor).translate(-imageCenterX, -imageCenterY));

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I've looked at the image viewer application example from Qt 4.5 examples, their code does a very good zooming in/out, and it keep the precision excellent, they use QLabel to load the QPixmap object, but its very very slow in zooming

scaleFactor *= factor;
imageLabel->resize(scaleFactor * imageLabel->pixmap()->size());

scaleFactor *= factor;
imageLabel->resize(scaleFactor * imageLabel->pixmap()->size());

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I've attached a sample pmb to show the difference between my app, and the image viewer app

mine is the one on the left (least precision), and image viewer is the right one

any comment is more than welcome

Best regards

[Lykurg]

did you use QGraphicsPixmapItem::setTransformationMode() with Qt::SmoothTransformation and/or QGraphicsView::setRenderHints() with QPainter::Antialiasing | QPainter::SmoothPixmapTransform?

[Scorp2us]

did you use QGraphicsPixmapItem::setTransformationMode() with Qt::SmoothTransformation and/or QGraphicsView::setRenderHints() with QPainter::Antialiasing | QPainter::SmoothPixmapTransform?

These should do it. IIRC, SmoothPixmapTransform is not default.